md/raid5: be more careful about write ordering when reshaping.

[safe/jmp/linux-2.6] / drivers / md / raid5.c

/*
 * raid5.c : Multiple Devices driver for Linux
 *         Copyright (C) 1996, 1997 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *         Copyright (C) 1999, 2000 Ingo Molnar
 *         Copyright (C) 2002, 2003 H. Peter Anvin
 *
 * RAID-4/5/6 management functions.
 * Thanks to Penguin Computing for making the RAID-6 development possible
 * by donating a test server!
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * BITMAP UNPLUGGING:
 *
 * The sequencing for updating the bitmap reliably is a little
 * subtle (and I got it wrong the first time) so it deserves some
 * explanation.
 *
 * We group bitmap updates into batches.  Each batch has a number.
 * We may write out several batches at once, but that isn't very important.
 * conf->bm_write is the number of the last batch successfully written.
 * conf->bm_flush is the number of the last batch that was closed to
 *    new additions.
 * When we discover that we will need to write to any block in a stripe
 * (in add_stripe_bio) we update the in-memory bitmap and record in sh->bm_seq
 * the number of the batch it will be in. This is bm_flush+1.
 * When we are ready to do a write, if that batch hasn't been written yet,
 *   we plug the array and queue the stripe for later.
 * When an unplug happens, we increment bm_flush, thus closing the current
 *   batch.
 * When we notice that bm_flush > bm_write, we write out all pending updates
 * to the bitmap, and advance bm_write to where bm_flush was.
 * This may occasionally write a bit out twice, but is sure never to
 * miss any bits.
 */

#include <linux/blkdev.h>
#include <linux/kthread.h>
#include <linux/raid/pq.h>
#include <linux/async_tx.h>
#include <linux/seq_file.h>
#include "md.h"
#include "raid5.h"
#include "bitmap.h"

/*
 * Stripe cache
 */

#define NR_STRIPES              256
#define STRIPE_SIZE             PAGE_SIZE
#define STRIPE_SHIFT            (PAGE_SHIFT - 9)
#define STRIPE_SECTORS          (STRIPE_SIZE>>9)
#define IO_THRESHOLD            1
#define BYPASS_THRESHOLD        1
#define NR_HASH                 (PAGE_SIZE / sizeof(struct hlist_head))
#define HASH_MASK               (NR_HASH - 1)

#define stripe_hash(conf, sect) (&((conf)->stripe_hashtbl[((sect) >> STRIPE_SHIFT) & HASH_MASK]))

/* bio's attached to a stripe+device for I/O are linked together in bi_sector
 * order without overlap.  There may be several bio's per stripe+device, and
 * a bio could span several devices.
 * When walking this list for a particular stripe+device, we must never proceed
 * beyond a bio that extends past this device, as the next bio might no longer
 * be valid.
 * This macro is used to determine the 'next' bio in the list, given the sector
 * of the current stripe+device
 */
#define r5_next_bio(bio, sect) ( ( (bio)->bi_sector + ((bio)->bi_size>>9) < sect + STRIPE_SECTORS) ? (bio)->bi_next : NULL)
/*
 * The following can be used to debug the driver
 */
#define RAID5_PARANOIA  1
#if RAID5_PARANOIA && defined(CONFIG_SMP)
# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
#else
# define CHECK_DEVLOCK()
#endif

#ifdef DEBUG
#define inline
#define __inline__
#endif

#define printk_rl(args...) ((void) (printk_ratelimit() && printk(args)))

/*
 * We maintain a biased count of active stripes in the bottom 16 bits of
 * bi_phys_segments, and a count of processed stripes in the upper 16 bits
 */
static inline int raid5_bi_phys_segments(struct bio *bio)
{
        return bio->bi_phys_segments & 0xffff;
}

static inline int raid5_bi_hw_segments(struct bio *bio)
{
        return (bio->bi_phys_segments >> 16) & 0xffff;
}

static inline int raid5_dec_bi_phys_segments(struct bio *bio)
{
        --bio->bi_phys_segments;
        return raid5_bi_phys_segments(bio);
}

static inline int raid5_dec_bi_hw_segments(struct bio *bio)
{
        unsigned short val = raid5_bi_hw_segments(bio);

        --val;
        bio->bi_phys_segments = (val << 16) | raid5_bi_phys_segments(bio);
        return val;
}

static inline void raid5_set_bi_hw_segments(struct bio *bio, unsigned int cnt)
{
        bio->bi_phys_segments = raid5_bi_phys_segments(bio) || (cnt << 16);
}

/* Find first data disk in a raid6 stripe */
static inline int raid6_d0(struct stripe_head *sh)
{
        if (sh->ddf_layout)
                /* ddf always start from first device */
                return 0;
        /* md starts just after Q block */
        if (sh->qd_idx == sh->disks - 1)
                return 0;
        else
                return sh->qd_idx + 1;
}
static inline int raid6_next_disk(int disk, int raid_disks)
{
        disk++;
        return (disk < raid_disks) ? disk : 0;
}

/* When walking through the disks in a raid5, starting at raid6_d0,
 * We need to map each disk to a 'slot', where the data disks are slot
 * 0 .. raid_disks-3, the parity disk is raid_disks-2 and the Q disk
 * is raid_disks-1.  This help does that mapping.
 */
static int raid6_idx_to_slot(int idx, struct stripe_head *sh,
                             int *count, int syndrome_disks)
{
        int slot;

        if (idx == sh->pd_idx)
                return syndrome_disks;
        if (idx == sh->qd_idx)
                return syndrome_disks + 1;
        slot = (*count)++;
        return slot;
}

static void return_io(struct bio *return_bi)
{
        struct bio *bi = return_bi;
        while (bi) {

                return_bi = bi->bi_next;
                bi->bi_next = NULL;
                bi->bi_size = 0;
                bio_endio(bi, 0);
                bi = return_bi;
        }
}

static void print_raid5_conf (raid5_conf_t *conf);

static int stripe_operations_active(struct stripe_head *sh)
{
        return sh->check_state || sh->reconstruct_state ||
               test_bit(STRIPE_BIOFILL_RUN, &sh->state) ||
               test_bit(STRIPE_COMPUTE_RUN, &sh->state);
}

static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
{
        if (atomic_dec_and_test(&sh->count)) {
                BUG_ON(!list_empty(&sh->lru));
                BUG_ON(atomic_read(&conf->active_stripes)==0);
                if (test_bit(STRIPE_HANDLE, &sh->state)) {
                        if (test_bit(STRIPE_DELAYED, &sh->state)) {
                                list_add_tail(&sh->lru, &conf->delayed_list);
                                blk_plug_device(conf->mddev->queue);
                        } else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
                                   sh->bm_seq - conf->seq_write > 0) {
                                list_add_tail(&sh->lru, &conf->bitmap_list);
                                blk_plug_device(conf->mddev->queue);
                        } else {
                                clear_bit(STRIPE_BIT_DELAY, &sh->state);
                                list_add_tail(&sh->lru, &conf->handle_list);
                        }
                        md_wakeup_thread(conf->mddev->thread);
                } else {
                        BUG_ON(stripe_operations_active(sh));
                        if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                atomic_dec(&conf->preread_active_stripes);
                                if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
                                        md_wakeup_thread(conf->mddev->thread);
                        }
                        atomic_dec(&conf->active_stripes);
                        if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
                                list_add_tail(&sh->lru, &conf->inactive_list);
                                wake_up(&conf->wait_for_stripe);
                                if (conf->retry_read_aligned)
                                        md_wakeup_thread(conf->mddev->thread);
                        }
                }
        }
}

static void release_stripe(struct stripe_head *sh)
{
        raid5_conf_t *conf = sh->raid_conf;
        unsigned long flags;

        spin_lock_irqsave(&conf->device_lock, flags);
        __release_stripe(conf, sh);
        spin_unlock_irqrestore(&conf->device_lock, flags);
}

static inline void remove_hash(struct stripe_head *sh)
{
        pr_debug("remove_hash(), stripe %llu\n",
                (unsigned long long)sh->sector);

        hlist_del_init(&sh->hash);
}

static inline void insert_hash(raid5_conf_t *conf, struct stripe_head *sh)
{
        struct hlist_head *hp = stripe_hash(conf, sh->sector);

        pr_debug("insert_hash(), stripe %llu\n",
                (unsigned long long)sh->sector);

        CHECK_DEVLOCK();
        hlist_add_head(&sh->hash, hp);
}


/* find an idle stripe, make sure it is unhashed, and return it. */
static struct stripe_head *get_free_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh = NULL;
        struct list_head *first;

        CHECK_DEVLOCK();
        if (list_empty(&conf->inactive_list))
                goto out;
        first = conf->inactive_list.next;
        sh = list_entry(first, struct stripe_head, lru);
        list_del_init(first);
        remove_hash(sh);
        atomic_inc(&conf->active_stripes);
out:
        return sh;
}

static void shrink_buffers(struct stripe_head *sh, int num)
{
        struct page *p;
        int i;

        for (i=0; i<num ; i++) {
                p = sh->dev[i].page;
                if (!p)
                        continue;
                sh->dev[i].page = NULL;
                put_page(p);
        }
}

static int grow_buffers(struct stripe_head *sh, int num)
{
        int i;

        for (i=0; i<num; i++) {
                struct page *page;

                if (!(page = alloc_page(GFP_KERNEL))) {
                        return 1;
                }
                sh->dev[i].page = page;
        }
        return 0;
}

static void raid5_build_block(struct stripe_head *sh, int i, int previous);
static void stripe_set_idx(sector_t stripe, raid5_conf_t *conf, int previous,
                            struct stripe_head *sh);

static void init_stripe(struct stripe_head *sh, sector_t sector, int previous)
{
        raid5_conf_t *conf = sh->raid_conf;
        int i;

        BUG_ON(atomic_read(&sh->count) != 0);
        BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
        BUG_ON(stripe_operations_active(sh));

        CHECK_DEVLOCK();
        pr_debug("init_stripe called, stripe %llu\n",
                (unsigned long long)sh->sector);

        remove_hash(sh);

        sh->generation = conf->generation - previous;
        sh->disks = previous ? conf->previous_raid_disks : conf->raid_disks;
        sh->sector = sector;
        stripe_set_idx(sector, conf, previous, sh);
        sh->state = 0;


        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                if (dev->toread || dev->read || dev->towrite || dev->written ||
                    test_bit(R5_LOCKED, &dev->flags)) {
                        printk(KERN_ERR "sector=%llx i=%d %p %p %p %p %d\n",
                               (unsigned long long)sh->sector, i, dev->toread,
                               dev->read, dev->towrite, dev->written,
                               test_bit(R5_LOCKED, &dev->flags));
                        BUG();
                }
                dev->flags = 0;
                raid5_build_block(sh, i, previous);
        }
        insert_hash(conf, sh);
}

static struct stripe_head *__find_stripe(raid5_conf_t *conf, sector_t sector,
                                         short generation)
{
        struct stripe_head *sh;
        struct hlist_node *hn;

        CHECK_DEVLOCK();
        pr_debug("__find_stripe, sector %llu\n", (unsigned long long)sector);
        hlist_for_each_entry(sh, hn, stripe_hash(conf, sector), hash)
                if (sh->sector == sector && sh->generation == generation)
                        return sh;
        pr_debug("__stripe %llu not in cache\n", (unsigned long long)sector);
        return NULL;
}

static void unplug_slaves(mddev_t *mddev);
static void raid5_unplug_device(struct request_queue *q);

static struct stripe_head *
get_active_stripe(raid5_conf_t *conf, sector_t sector,
                  int previous, int noblock)
{
        struct stripe_head *sh;

        pr_debug("get_stripe, sector %llu\n", (unsigned long long)sector);

        spin_lock_irq(&conf->device_lock);

        do {
                wait_event_lock_irq(conf->wait_for_stripe,
                                    conf->quiesce == 0,
                                    conf->device_lock, /* nothing */);
                sh = __find_stripe(conf, sector, conf->generation - previous);
                if (!sh) {
                        if (!conf->inactive_blocked)
                                sh = get_free_stripe(conf);
                        if (noblock && sh == NULL)
                                break;
                        if (!sh) {
                                conf->inactive_blocked = 1;
                                wait_event_lock_irq(conf->wait_for_stripe,
                                                    !list_empty(&conf->inactive_list) &&
                                                    (atomic_read(&conf->active_stripes)
                                                     < (conf->max_nr_stripes *3/4)
                                                     || !conf->inactive_blocked),
                                                    conf->device_lock,
                                                    raid5_unplug_device(conf->mddev->queue)
                                        );
                                conf->inactive_blocked = 0;
                        } else
                                init_stripe(sh, sector, previous);
                } else {
                        if (atomic_read(&sh->count)) {
                                BUG_ON(!list_empty(&sh->lru)
                                    && !test_bit(STRIPE_EXPANDING, &sh->state));
                        } else {
                                if (!test_bit(STRIPE_HANDLE, &sh->state))
                                        atomic_inc(&conf->active_stripes);
                                if (list_empty(&sh->lru) &&
                                    !test_bit(STRIPE_EXPANDING, &sh->state))
                                        BUG();
                                list_del_init(&sh->lru);
                        }
                }
        } while (sh == NULL);

        if (sh)
                atomic_inc(&sh->count);

        spin_unlock_irq(&conf->device_lock);
        return sh;
}

static void
raid5_end_read_request(struct bio *bi, int error);
static void
raid5_end_write_request(struct bio *bi, int error);

static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
{
        raid5_conf_t *conf = sh->raid_conf;
        int i, disks = sh->disks;

        might_sleep();

        for (i = disks; i--; ) {
                int rw;
                struct bio *bi;
                mdk_rdev_t *rdev;
                if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
                        rw = WRITE;
                else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
                        rw = READ;
                else
                        continue;

                bi = &sh->dev[i].req;

                bi->bi_rw = rw;
                if (rw == WRITE)
                        bi->bi_end_io = raid5_end_write_request;
                else
                        bi->bi_end_io = raid5_end_read_request;

                rcu_read_lock();
                rdev = rcu_dereference(conf->disks[i].rdev);
                if (rdev && test_bit(Faulty, &rdev->flags))
                        rdev = NULL;
                if (rdev)
                        atomic_inc(&rdev->nr_pending);
                rcu_read_unlock();

                if (rdev) {
                        if (s->syncing || s->expanding || s->expanded)
                                md_sync_acct(rdev->bdev, STRIPE_SECTORS);

                        set_bit(STRIPE_IO_STARTED, &sh->state);

                        bi->bi_bdev = rdev->bdev;
                        pr_debug("%s: for %llu schedule op %ld on disc %d\n",
                                __func__, (unsigned long long)sh->sector,
                                bi->bi_rw, i);
                        atomic_inc(&sh->count);
                        bi->bi_sector = sh->sector + rdev->data_offset;
                        bi->bi_flags = 1 << BIO_UPTODATE;
                        bi->bi_vcnt = 1;
                        bi->bi_max_vecs = 1;
                        bi->bi_idx = 0;
                        bi->bi_io_vec = &sh->dev[i].vec;
                        bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
                        bi->bi_io_vec[0].bv_offset = 0;
                        bi->bi_size = STRIPE_SIZE;
                        bi->bi_next = NULL;
                        if (rw == WRITE &&
                            test_bit(R5_ReWrite, &sh->dev[i].flags))
                                atomic_add(STRIPE_SECTORS,
                                        &rdev->corrected_errors);
                        generic_make_request(bi);
                } else {
                        if (rw == WRITE)
                                set_bit(STRIPE_DEGRADED, &sh->state);
                        pr_debug("skip op %ld on disc %d for sector %llu\n",
                                bi->bi_rw, i, (unsigned long long)sh->sector);
                        clear_bit(R5_LOCKED, &sh->dev[i].flags);
                        set_bit(STRIPE_HANDLE, &sh->state);
                }
        }
}

static struct dma_async_tx_descriptor *
async_copy_data(int frombio, struct bio *bio, struct page *page,
        sector_t sector, struct dma_async_tx_descriptor *tx)
{
        struct bio_vec *bvl;
        struct page *bio_page;
        int i;
        int page_offset;

        if (bio->bi_sector >= sector)
                page_offset = (signed)(bio->bi_sector - sector) * 512;
        else
                page_offset = (signed)(sector - bio->bi_sector) * -512;
        bio_for_each_segment(bvl, bio, i) {
                int len = bio_iovec_idx(bio, i)->bv_len;
                int clen;
                int b_offset = 0;

                if (page_offset < 0) {
                        b_offset = -page_offset;
                        page_offset += b_offset;
                        len -= b_offset;
                }

                if (len > 0 && page_offset + len > STRIPE_SIZE)
                        clen = STRIPE_SIZE - page_offset;
                else
                        clen = len;

                if (clen > 0) {
                        b_offset += bio_iovec_idx(bio, i)->bv_offset;
                        bio_page = bio_iovec_idx(bio, i)->bv_page;
                        if (frombio)
                                tx = async_memcpy(page, bio_page, page_offset,
                                        b_offset, clen,
                                        ASYNC_TX_DEP_ACK,
                                        tx, NULL, NULL);
                        else
                                tx = async_memcpy(bio_page, page, b_offset,
                                        page_offset, clen,
                                        ASYNC_TX_DEP_ACK,
                                        tx, NULL, NULL);
                }
                if (clen < len) /* hit end of page */
                        break;
                page_offset +=  len;
        }

        return tx;
}

static void ops_complete_biofill(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        struct bio *return_bi = NULL;
        raid5_conf_t *conf = sh->raid_conf;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* clear completed biofills */
        spin_lock_irq(&conf->device_lock);
        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                /* acknowledge completion of a biofill operation */
                /* and check if we need to reply to a read request,
                 * new R5_Wantfill requests are held off until
                 * !STRIPE_BIOFILL_RUN
                 */
                if (test_and_clear_bit(R5_Wantfill, &dev->flags)) {
                        struct bio *rbi, *rbi2;

                        BUG_ON(!dev->read);
                        rbi = dev->read;
                        dev->read = NULL;
                        while (rbi && rbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                rbi2 = r5_next_bio(rbi, dev->sector);
                                if (!raid5_dec_bi_phys_segments(rbi)) {
                                        rbi->bi_next = return_bi;
                                        return_bi = rbi;
                                }
                                rbi = rbi2;
                        }
                }
        }
        spin_unlock_irq(&conf->device_lock);
        clear_bit(STRIPE_BIOFILL_RUN, &sh->state);

        return_io(return_bi);

        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void ops_run_biofill(struct stripe_head *sh)
{
        struct dma_async_tx_descriptor *tx = NULL;
        raid5_conf_t *conf = sh->raid_conf;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (test_bit(R5_Wantfill, &dev->flags)) {
                        struct bio *rbi;
                        spin_lock_irq(&conf->device_lock);
                        dev->read = rbi = dev->toread;
                        dev->toread = NULL;
                        spin_unlock_irq(&conf->device_lock);
                        while (rbi && rbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                tx = async_copy_data(0, rbi, dev->page,
                                        dev->sector, tx);
                                rbi = r5_next_bio(rbi, dev->sector);
                        }
                }
        }

        atomic_inc(&sh->count);
        async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
                ops_complete_biofill, sh);
}

static void ops_complete_compute5(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        int target = sh->ops.target;
        struct r5dev *tgt = &sh->dev[target];

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        set_bit(R5_UPTODATE, &tgt->flags);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
        clear_bit(R5_Wantcompute, &tgt->flags);
        clear_bit(STRIPE_COMPUTE_RUN, &sh->state);
        if (sh->check_state == check_state_compute_run)
                sh->check_state = check_state_compute_result;
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static struct dma_async_tx_descriptor *ops_run_compute5(struct stripe_head *sh)
{
        /* kernel stack size limits the total number of disks */
        int disks = sh->disks;
        struct page *xor_srcs[disks];
        int target = sh->ops.target;
        struct r5dev *tgt = &sh->dev[target];
        struct page *xor_dest = tgt->page;
        int count = 0;
        struct dma_async_tx_descriptor *tx;
        int i;

        pr_debug("%s: stripe %llu block: %d\n",
                __func__, (unsigned long long)sh->sector, target);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));

        for (i = disks; i--; )
                if (i != target)
                        xor_srcs[count++] = sh->dev[i].page;

        atomic_inc(&sh->count);

        if (unlikely(count == 1))
                tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE,
                        0, NULL, ops_complete_compute5, sh);
        else
                tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                        ASYNC_TX_XOR_ZERO_DST, NULL,
                        ops_complete_compute5, sh);

        return tx;
}

static void ops_complete_prexor(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);
}

static struct dma_async_tx_descriptor *
ops_run_prexor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
        /* kernel stack size limits the total number of disks */
        int disks = sh->disks;
        struct page *xor_srcs[disks];
        int count = 0, pd_idx = sh->pd_idx, i;

        /* existing parity data subtracted */
        struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                /* Only process blocks that are known to be uptodate */
                if (test_bit(R5_Wantdrain, &dev->flags))
                        xor_srcs[count++] = dev->page;
        }

        tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                ASYNC_TX_DEP_ACK | ASYNC_TX_XOR_DROP_DST, tx,
                ops_complete_prexor, sh);

        return tx;
}

static struct dma_async_tx_descriptor *
ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
        int disks = sh->disks;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                struct bio *chosen;

                if (test_and_clear_bit(R5_Wantdrain, &dev->flags)) {
                        struct bio *wbi;

                        spin_lock(&sh->lock);
                        chosen = dev->towrite;
                        dev->towrite = NULL;
                        BUG_ON(dev->written);
                        wbi = dev->written = chosen;
                        spin_unlock(&sh->lock);

                        while (wbi && wbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                tx = async_copy_data(1, wbi, dev->page,
                                        dev->sector, tx);
                                wbi = r5_next_bio(wbi, dev->sector);
                        }
                }
        }

        return tx;
}

static void ops_complete_postxor(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        int disks = sh->disks, i, pd_idx = sh->pd_idx;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (dev->written || i == pd_idx)
                        set_bit(R5_UPTODATE, &dev->flags);
        }

        if (sh->reconstruct_state == reconstruct_state_drain_run)
                sh->reconstruct_state = reconstruct_state_drain_result;
        else if (sh->reconstruct_state == reconstruct_state_prexor_drain_run)
                sh->reconstruct_state = reconstruct_state_prexor_drain_result;
        else {
                BUG_ON(sh->reconstruct_state != reconstruct_state_run);
                sh->reconstruct_state = reconstruct_state_result;
        }

        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void
ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
        /* kernel stack size limits the total number of disks */
        int disks = sh->disks;
        struct page *xor_srcs[disks];

        int count = 0, pd_idx = sh->pd_idx, i;
        struct page *xor_dest;
        int prexor = 0;
        unsigned long flags;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* check if prexor is active which means only process blocks
         * that are part of a read-modify-write (written)
         */
        if (sh->reconstruct_state == reconstruct_state_prexor_drain_run) {
                prexor = 1;
                xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (dev->written)
                                xor_srcs[count++] = dev->page;
                }
        } else {
                xor_dest = sh->dev[pd_idx].page;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (i != pd_idx)
                                xor_srcs[count++] = dev->page;
                }
        }

        /* 1/ if we prexor'd then the dest is reused as a source
         * 2/ if we did not prexor then we are redoing the parity
         * set ASYNC_TX_XOR_DROP_DST and ASYNC_TX_XOR_ZERO_DST
         * for the synchronous xor case
         */
        flags = ASYNC_TX_DEP_ACK | ASYNC_TX_ACK |
                (prexor ? ASYNC_TX_XOR_DROP_DST : ASYNC_TX_XOR_ZERO_DST);

        atomic_inc(&sh->count);

        if (unlikely(count == 1)) {
                flags &= ~(ASYNC_TX_XOR_DROP_DST | ASYNC_TX_XOR_ZERO_DST);
                tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE,
                        flags, tx, ops_complete_postxor, sh);
        } else
                tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                        flags, tx, ops_complete_postxor, sh);
}

static void ops_complete_check(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        sh->check_state = check_state_check_result;
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void ops_run_check(struct stripe_head *sh)
{
        /* kernel stack size limits the total number of disks */
        int disks = sh->disks;
        struct page *xor_srcs[disks];
        struct dma_async_tx_descriptor *tx;

        int count = 0, pd_idx = sh->pd_idx, i;
        struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (i != pd_idx)
                        xor_srcs[count++] = dev->page;
        }

        tx = async_xor_zero_sum(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                &sh->ops.zero_sum_result, 0, NULL, NULL, NULL);

        atomic_inc(&sh->count);
        tx = async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
                ops_complete_check, sh);
}

static void raid5_run_ops(struct stripe_head *sh, unsigned long ops_request)
{
        int overlap_clear = 0, i, disks = sh->disks;
        struct dma_async_tx_descriptor *tx = NULL;

        if (test_bit(STRIPE_OP_BIOFILL, &ops_request)) {
                ops_run_biofill(sh);
                overlap_clear++;
        }

        if (test_bit(STRIPE_OP_COMPUTE_BLK, &ops_request)) {
                tx = ops_run_compute5(sh);
                /* terminate the chain if postxor is not set to be run */
                if (tx && !test_bit(STRIPE_OP_POSTXOR, &ops_request))
                        async_tx_ack(tx);
        }

        if (test_bit(STRIPE_OP_PREXOR, &ops_request))
                tx = ops_run_prexor(sh, tx);

        if (test_bit(STRIPE_OP_BIODRAIN, &ops_request)) {
                tx = ops_run_biodrain(sh, tx);
                overlap_clear++;
        }

        if (test_bit(STRIPE_OP_POSTXOR, &ops_request))
                ops_run_postxor(sh, tx);

        if (test_bit(STRIPE_OP_CHECK, &ops_request))
                ops_run_check(sh);

        if (overlap_clear)
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (test_and_clear_bit(R5_Overlap, &dev->flags))
                                wake_up(&sh->raid_conf->wait_for_overlap);
                }
}

static int grow_one_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh;
        sh = kmem_cache_alloc(conf->slab_cache, GFP_KERNEL);
        if (!sh)
                return 0;
        memset(sh, 0, sizeof(*sh) + (conf->raid_disks-1)*sizeof(struct r5dev));
        sh->raid_conf = conf;
        spin_lock_init(&sh->lock);

        if (grow_buffers(sh, conf->raid_disks)) {
                shrink_buffers(sh, conf->raid_disks);
                kmem_cache_free(conf->slab_cache, sh);
                return 0;
        }
        sh->disks = conf->raid_disks;
        /* we just created an active stripe so... */
        atomic_set(&sh->count, 1);
        atomic_inc(&conf->active_stripes);
        INIT_LIST_HEAD(&sh->lru);
        release_stripe(sh);
        return 1;
}

static int grow_stripes(raid5_conf_t *conf, int num)
{
        struct kmem_cache *sc;
        int devs = conf->raid_disks;

        sprintf(conf->cache_name[0],
                "raid%d-%s", conf->level, mdname(conf->mddev));
        sprintf(conf->cache_name[1],
                "raid%d-%s-alt", conf->level, mdname(conf->mddev));
        conf->active_name = 0;
        sc = kmem_cache_create(conf->cache_name[conf->active_name],
                               sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
                               0, 0, NULL);
        if (!sc)
                return 1;
        conf->slab_cache = sc;
        conf->pool_size = devs;
        while (num--)
                if (!grow_one_stripe(conf))
                        return 1;
        return 0;
}

#ifdef CONFIG_MD_RAID5_RESHAPE
static int resize_stripes(raid5_conf_t *conf, int newsize)
{
        /* Make all the stripes able to hold 'newsize' devices.
         * New slots in each stripe get 'page' set to a new page.
         *
         * This happens in stages:
         * 1/ create a new kmem_cache and allocate the required number of
         *    stripe_heads.
         * 2/ gather all the old stripe_heads and tranfer the pages across
         *    to the new stripe_heads.  This will have the side effect of
         *    freezing the array as once all stripe_heads have been collected,
         *    no IO will be possible.  Old stripe heads are freed once their
         *    pages have been transferred over, and the old kmem_cache is
         *    freed when all stripes are done.
         * 3/ reallocate conf->disks to be suitable bigger.  If this fails,
         *    we simple return a failre status - no need to clean anything up.
         * 4/ allocate new pages for the new slots in the new stripe_heads.
         *    If this fails, we don't bother trying the shrink the
         *    stripe_heads down again, we just leave them as they are.
         *    As each stripe_head is processed the new one is released into
         *    active service.
         *
         * Once step2 is started, we cannot afford to wait for a write,
         * so we use GFP_NOIO allocations.
         */
        struct stripe_head *osh, *nsh;
        LIST_HEAD(newstripes);
        struct disk_info *ndisks;
        int err;
        struct kmem_cache *sc;
        int i;

        if (newsize <= conf->pool_size)
                return 0; /* never bother to shrink */

        err = md_allow_write(conf->mddev);
        if (err)
                return err;

        /* Step 1 */
        sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
                               sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
                               0, 0, NULL);
        if (!sc)
                return -ENOMEM;

        for (i = conf->max_nr_stripes; i; i--) {
                nsh = kmem_cache_alloc(sc, GFP_KERNEL);
                if (!nsh)
                        break;

                memset(nsh, 0, sizeof(*nsh) + (newsize-1)*sizeof(struct r5dev));

                nsh->raid_conf = conf;
                spin_lock_init(&nsh->lock);

                list_add(&nsh->lru, &newstripes);
        }
        if (i) {
                /* didn't get enough, give up */
                while (!list_empty(&newstripes)) {
                        nsh = list_entry(newstripes.next, struct stripe_head, lru);
                        list_del(&nsh->lru);
                        kmem_cache_free(sc, nsh);
                }
                kmem_cache_destroy(sc);
                return -ENOMEM;
        }
        /* Step 2 - Must use GFP_NOIO now.
         * OK, we have enough stripes, start collecting inactive
         * stripes and copying them over
         */
        list_for_each_entry(nsh, &newstripes, lru) {
                spin_lock_irq(&conf->device_lock);
                wait_event_lock_irq(conf->wait_for_stripe,
                                    !list_empty(&conf->inactive_list),
                                    conf->device_lock,
                                    unplug_slaves(conf->mddev)
                        );
                osh = get_free_stripe(conf);
                spin_unlock_irq(&conf->device_lock);
                atomic_set(&nsh->count, 1);
                for(i=0; i<conf->pool_size; i++)
                        nsh->dev[i].page = osh->dev[i].page;
                for( ; i<newsize; i++)
                        nsh->dev[i].page = NULL;
                kmem_cache_free(conf->slab_cache, osh);
        }
        kmem_cache_destroy(conf->slab_cache);

        /* Step 3.
         * At this point, we are holding all the stripes so the array
         * is completely stalled, so now is a good time to resize
         * conf->disks.
         */
        ndisks = kzalloc(newsize * sizeof(struct disk_info), GFP_NOIO);
        if (ndisks) {
                for (i=0; i<conf->raid_disks; i++)
                        ndisks[i] = conf->disks[i];
                kfree(conf->disks);
                conf->disks = ndisks;
        } else
                err = -ENOMEM;

        /* Step 4, return new stripes to service */
        while(!list_empty(&newstripes)) {
                nsh = list_entry(newstripes.next, struct stripe_head, lru);
                list_del_init(&nsh->lru);
                for (i=conf->raid_disks; i < newsize; i++)
                        if (nsh->dev[i].page == NULL) {
                                struct page *p = alloc_page(GFP_NOIO);
                                nsh->dev[i].page = p;
                                if (!p)
                                        err = -ENOMEM;
                        }
                release_stripe(nsh);
        }
        /* critical section pass, GFP_NOIO no longer needed */

        conf->slab_cache = sc;
        conf->active_name = 1-conf->active_name;
        conf->pool_size = newsize;
        return err;
}
#endif

static int drop_one_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh;

        spin_lock_irq(&conf->device_lock);
        sh = get_free_stripe(conf);
        spin_unlock_irq(&conf->device_lock);
        if (!sh)
                return 0;
        BUG_ON(atomic_read(&sh->count));
        shrink_buffers(sh, conf->pool_size);
        kmem_cache_free(conf->slab_cache, sh);
        atomic_dec(&conf->active_stripes);
        return 1;
}

static void shrink_stripes(raid5_conf_t *conf)
{
        while (drop_one_stripe(conf))
                ;

        if (conf->slab_cache)
                kmem_cache_destroy(conf->slab_cache);
        conf->slab_cache = NULL;
}

static void raid5_end_read_request(struct bio * bi, int error)
{
        struct stripe_head *sh = bi->bi_private;
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks, i;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
        char b[BDEVNAME_SIZE];
        mdk_rdev_t *rdev;


        for (i=0 ; i<disks; i++)
                if (bi == &sh->dev[i].req)
                        break;

        pr_debug("end_read_request %llu/%d, count: %d, uptodate %d.\n",
                (unsigned long long)sh->sector, i, atomic_read(&sh->count),
                uptodate);
        if (i == disks) {
                BUG();
                return;
        }

        if (uptodate) {
                set_bit(R5_UPTODATE, &sh->dev[i].flags);
                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        rdev = conf->disks[i].rdev;
                        printk_rl(KERN_INFO "raid5:%s: read error corrected"
                                  " (%lu sectors at %llu on %s)\n",
                                  mdname(conf->mddev), STRIPE_SECTORS,
                                  (unsigned long long)(sh->sector
                                                       + rdev->data_offset),
                                  bdevname(rdev->bdev, b));
                        clear_bit(R5_ReadError, &sh->dev[i].flags);
                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
                }
                if (atomic_read(&conf->disks[i].rdev->read_errors))
                        atomic_set(&conf->disks[i].rdev->read_errors, 0);
        } else {
                const char *bdn = bdevname(conf->disks[i].rdev->bdev, b);
                int retry = 0;
                rdev = conf->disks[i].rdev;

                clear_bit(R5_UPTODATE, &sh->dev[i].flags);
                atomic_inc(&rdev->read_errors);
                if (conf->mddev->degraded)
                        printk_rl(KERN_WARNING
                                  "raid5:%s: read error not correctable "
                                  "(sector %llu on %s).\n",
                                  mdname(conf->mddev),
                                  (unsigned long long)(sh->sector
                                                       + rdev->data_offset),
                                  bdn);
                else if (test_bit(R5_ReWrite, &sh->dev[i].flags))
                        /* Oh, no!!! */
                        printk_rl(KERN_WARNING
                                  "raid5:%s: read error NOT corrected!! "
                                  "(sector %llu on %s).\n",
                                  mdname(conf->mddev),
                                  (unsigned long long)(sh->sector
                                                       + rdev->data_offset),
                                  bdn);
                else if (atomic_read(&rdev->read_errors)
                         > conf->max_nr_stripes)
                        printk(KERN_WARNING
                               "raid5:%s: Too many read errors, failing device %s.\n",
                               mdname(conf->mddev), bdn);
                else
                        retry = 1;
                if (retry)
                        set_bit(R5_ReadError, &sh->dev[i].flags);
                else {
                        clear_bit(R5_ReadError, &sh->dev[i].flags);
                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
                        md_error(conf->mddev, rdev);
                }
        }
        rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
        clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void raid5_end_write_request(struct bio *bi, int error)
{
        struct stripe_head *sh = bi->bi_private;
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks, i;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);

        for (i=0 ; i<disks; i++)
                if (bi == &sh->dev[i].req)
                        break;

        pr_debug("end_write_request %llu/%d, count %d, uptodate: %d.\n",
                (unsigned long long)sh->sector, i, atomic_read(&sh->count),
                uptodate);
        if (i == disks) {
                BUG();
                return;
        }

        if (!uptodate)
                md_error(conf->mddev, conf->disks[i].rdev);

        rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
        
        clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}


static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous);
        
static void raid5_build_block(struct stripe_head *sh, int i, int previous)
{
        struct r5dev *dev = &sh->dev[i];

        bio_init(&dev->req);
        dev->req.bi_io_vec = &dev->vec;
        dev->req.bi_vcnt++;
        dev->req.bi_max_vecs++;
        dev->vec.bv_page = dev->page;
        dev->vec.bv_len = STRIPE_SIZE;
        dev->vec.bv_offset = 0;

        dev->req.bi_sector = sh->sector;
        dev->req.bi_private = sh;

        dev->flags = 0;
        dev->sector = compute_blocknr(sh, i, previous);
}

static void error(mddev_t *mddev, mdk_rdev_t *rdev)
{
        char b[BDEVNAME_SIZE];
        raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
        pr_debug("raid5: error called\n");

        if (!test_bit(Faulty, &rdev->flags)) {
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                if (test_and_clear_bit(In_sync, &rdev->flags)) {
                        unsigned long flags;
                        spin_lock_irqsave(&conf->device_lock, flags);
                        mddev->degraded++;
                        spin_unlock_irqrestore(&conf->device_lock, flags);
                        /*
                         * if recovery was running, make sure it aborts.
                         */
                        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
                }
                set_bit(Faulty, &rdev->flags);
                printk(KERN_ALERT
                       "raid5: Disk failure on %s, disabling device.\n"
                       "raid5: Operation continuing on %d devices.\n",
                       bdevname(rdev->bdev,b), conf->raid_disks - mddev->degraded);
        }
}

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
                                     int previous, int *dd_idx,
                                     struct stripe_head *sh)
{
        long stripe;
        unsigned long chunk_number;
        unsigned int chunk_offset;
        int pd_idx, qd_idx;
        int ddf_layout = 0;
        sector_t new_sector;
        int algorithm = previous ? conf->prev_algo
                                 : conf->algorithm;
        int sectors_per_chunk = previous ? (conf->prev_chunk >> 9)
                                         : (conf->chunk_size >> 9);
        int raid_disks = previous ? conf->previous_raid_disks
                                  : conf->raid_disks;
        int data_disks = raid_disks - conf->max_degraded;

        /* First compute the information on this sector */

        /*
         * Compute the chunk number and the sector offset inside the chunk
         */
        chunk_offset = sector_div(r_sector, sectors_per_chunk);
        chunk_number = r_sector;
        BUG_ON(r_sector != chunk_number);

        /*
         * Compute the stripe number
         */
        stripe = chunk_number / data_disks;

        /*
         * Compute the data disk and parity disk indexes inside the stripe
         */
        *dd_idx = chunk_number % data_disks;

        /*
         * Select the parity disk based on the user selected algorithm.
         */
        pd_idx = qd_idx = ~0;
        switch(conf->level) {
        case 4:
                pd_idx = data_disks;
                break;
        case 5:
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                        pd_idx = data_disks - stripe % raid_disks;
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        break;
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        pd_idx = stripe % raid_disks;
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                        pd_idx = data_disks - stripe % raid_disks;
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_RIGHT_SYMMETRIC:
                        pd_idx = stripe % raid_disks;
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_PARITY_0:
                        pd_idx = 0;
                        (*dd_idx)++;
                        break;
                case ALGORITHM_PARITY_N:
                        pd_idx = data_disks;
                        break;
                default:
                        printk(KERN_ERR "raid5: unsupported algorithm %d\n",
                                algorithm);
                        BUG();
                }
                break;
        case 6:

                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                        pd_idx = raid_disks - 1 - (stripe % raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        break;
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        pd_idx = stripe % raid_disks;
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                        pd_idx = raid_disks - 1 - (stripe % raid_disks);
                        qd_idx = (pd_idx + 1) % raid_disks;
                        *dd_idx = (pd_idx + 2 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_RIGHT_SYMMETRIC:
                        pd_idx = stripe % raid_disks;
                        qd_idx = (pd_idx + 1) % raid_disks;
                        *dd_idx = (pd_idx + 2 + *dd_idx) % raid_disks;
                        break;

                case ALGORITHM_PARITY_0:
                        pd_idx = 0;
                        qd_idx = 1;
                        (*dd_idx) += 2;
                        break;
                case ALGORITHM_PARITY_N:
                        pd_idx = data_disks;
                        qd_idx = data_disks + 1;
                        break;

                case ALGORITHM_ROTATING_ZERO_RESTART:
                        /* Exactly the same as RIGHT_ASYMMETRIC, but or
                         * of blocks for computing Q is different.
                         */
                        pd_idx = stripe % raid_disks;
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        ddf_layout = 1;
                        break;

                case ALGORITHM_ROTATING_N_RESTART:
                        /* Same a left_asymmetric, by first stripe is
                         * D D D P Q  rather than
                         * Q D D D P
                         */
                        pd_idx = raid_disks - 1 - ((stripe + 1) % raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        ddf_layout = 1;
                        break;

                case ALGORITHM_ROTATING_N_CONTINUE:
                        /* Same as left_symmetric but Q is before P */
                        pd_idx = raid_disks - 1 - (stripe % raid_disks);
                        qd_idx = (pd_idx + raid_disks - 1) % raid_disks;
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        ddf_layout = 1;
                        break;

                case ALGORITHM_LEFT_ASYMMETRIC_6:
                        /* RAID5 left_asymmetric, with Q on last device */
                        pd_idx = data_disks - stripe % (raid_disks-1);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_RIGHT_ASYMMETRIC_6:
                        pd_idx = stripe % (raid_disks-1);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_LEFT_SYMMETRIC_6:
                        pd_idx = data_disks - stripe % (raid_disks-1);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % (raid_disks-1);
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_RIGHT_SYMMETRIC_6:
                        pd_idx = stripe % (raid_disks-1);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % (raid_disks-1);
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_PARITY_0_6:
                        pd_idx = 0;
                        (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;


                default:
                        printk(KERN_CRIT "raid6: unsupported algorithm %d\n",
                               algorithm);
                        BUG();
                }
                break;
        }

        if (sh) {
                sh->pd_idx = pd_idx;
                sh->qd_idx = qd_idx;
                sh->ddf_layout = ddf_layout;
        }
        /*
         * Finally, compute the new sector number
         */
        new_sector = (sector_t)stripe * sectors_per_chunk + chunk_offset;
        return new_sector;
}


static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous)
{
        raid5_conf_t *conf = sh->raid_conf;
        int raid_disks = sh->disks;
        int data_disks = raid_disks - conf->max_degraded;
        sector_t new_sector = sh->sector, check;
        int sectors_per_chunk = previous ? (conf->prev_chunk >> 9)
                                         : (conf->chunk_size >> 9);
        int algorithm = previous ? conf->prev_algo
                                 : conf->algorithm;
        sector_t stripe;
        int chunk_offset;
        int chunk_number, dummy1, dd_idx = i;
        sector_t r_sector;
        struct stripe_head sh2;


        chunk_offset = sector_div(new_sector, sectors_per_chunk);
        stripe = new_sector;
        BUG_ON(new_sector != stripe);

        if (i == sh->pd_idx)
                return 0;
        switch(conf->level) {
        case 4: break;
        case 5:
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        if (i > sh->pd_idx)
                                i--;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                case ALGORITHM_RIGHT_SYMMETRIC:
                        if (i < sh->pd_idx)
                                i += raid_disks;
                        i -= (sh->pd_idx + 1);
                        break;
                case ALGORITHM_PARITY_0:
                        i -= 1;
                        break;
                case ALGORITHM_PARITY_N:
                        break;
                default:
                        printk(KERN_ERR "raid5: unsupported algorithm %d\n",
                               algorithm);
                        BUG();
                }
                break;
        case 6:
                if (i == sh->qd_idx)
                        return 0; /* It is the Q disk */
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                case ALGORITHM_ROTATING_ZERO_RESTART:
                case ALGORITHM_ROTATING_N_RESTART:
                        if (sh->pd_idx == raid_disks-1)
                                i--;    /* Q D D D P */
                        else if (i > sh->pd_idx)
                                i -= 2; /* D D P Q D */
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                case ALGORITHM_RIGHT_SYMMETRIC:
                        if (sh->pd_idx == raid_disks-1)
                                i--; /* Q D D D P */
                        else {
                                /* D D P Q D */
                                if (i < sh->pd_idx)
                                        i += raid_disks;
                                i -= (sh->pd_idx + 2);
                        }
                        break;
                case ALGORITHM_PARITY_0:
                        i -= 2;
                        break;
                case ALGORITHM_PARITY_N:
                        break;
                case ALGORITHM_ROTATING_N_CONTINUE:
                        if (sh->pd_idx == 0)
                                i--;    /* P D D D Q */
                        else if (i > sh->pd_idx)
                                i -= 2; /* D D Q P D */
                        break;
                case ALGORITHM_LEFT_ASYMMETRIC_6:
                case ALGORITHM_RIGHT_ASYMMETRIC_6:
                        if (i > sh->pd_idx)
                                i--;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC_6:
                case ALGORITHM_RIGHT_SYMMETRIC_6:
                        if (i < sh->pd_idx)
                                i += data_disks + 1;
                        i -= (sh->pd_idx + 1);
                        break;
                case ALGORITHM_PARITY_0_6:
                        i -= 1;
                        break;
                default:
                        printk(KERN_CRIT "raid6: unsupported algorithm %d\n",
                               algorithm);
                        BUG();
                }
                break;
        }

        chunk_number = stripe * data_disks + i;
        r_sector = (sector_t)chunk_number * sectors_per_chunk + chunk_offset;

        check = raid5_compute_sector(conf, r_sector,
                                     previous, &dummy1, &sh2);
        if (check != sh->sector || dummy1 != dd_idx || sh2.pd_idx != sh->pd_idx
                || sh2.qd_idx != sh->qd_idx) {
                printk(KERN_ERR "compute_blocknr: map not correct\n");
                return 0;
        }
        return r_sector;
}



/*
 * Copy data between a page in the stripe cache, and one or more bion
 * The page could align with the middle of the bio, or there could be
 * several bion, each with several bio_vecs, which cover part of the page
 * Multiple bion are linked together on bi_next.  There may be extras
 * at the end of this list.  We ignore them.
 */
static void copy_data(int frombio, struct bio *bio,
                     struct page *page,
                     sector_t sector)
{
        char *pa = page_address(page);
        struct bio_vec *bvl;
        int i;
        int page_offset;

        if (bio->bi_sector >= sector)
                page_offset = (signed)(bio->bi_sector - sector) * 512;
        else
                page_offset = (signed)(sector - bio->bi_sector) * -512;
        bio_for_each_segment(bvl, bio, i) {
                int len = bio_iovec_idx(bio,i)->bv_len;
                int clen;
                int b_offset = 0;

                if (page_offset < 0) {
                        b_offset = -page_offset;
                        page_offset += b_offset;
                        len -= b_offset;
                }

                if (len > 0 && page_offset + len > STRIPE_SIZE)
                        clen = STRIPE_SIZE - page_offset;
                else clen = len;

                if (clen > 0) {
                        char *ba = __bio_kmap_atomic(bio, i, KM_USER0);
                        if (frombio)
                                memcpy(pa+page_offset, ba+b_offset, clen);
                        else
                                memcpy(ba+b_offset, pa+page_offset, clen);
                        __bio_kunmap_atomic(ba, KM_USER0);
                }
                if (clen < len) /* hit end of page */
                        break;
                page_offset +=  len;
        }
}

#define check_xor()     do {                                              \
                                if (count == MAX_XOR_BLOCKS) {            \
                                xor_blocks(count, STRIPE_SIZE, dest, ptr);\
                                count = 0;                                \
                           }                                              \
                        } while(0)

static void compute_parity6(struct stripe_head *sh, int method)
{
        raid5_conf_t *conf = sh->raid_conf;
        int i, pd_idx, qd_idx, d0_idx, disks = sh->disks, count;
        int syndrome_disks = sh->ddf_layout ? disks : (disks - 2);
        struct bio *chosen;
        /**** FIX THIS: This could be very bad if disks is close to 256 ****/
        void *ptrs[syndrome_disks+2];

        pd_idx = sh->pd_idx;
        qd_idx = sh->qd_idx;
        d0_idx = raid6_d0(sh);

        pr_debug("compute_parity, stripe %llu, method %d\n",
                (unsigned long long)sh->sector, method);

        switch(method) {
        case READ_MODIFY_WRITE:
                BUG();          /* READ_MODIFY_WRITE N/A for RAID-6 */
        case RECONSTRUCT_WRITE:
                for (i= disks; i-- ;)
                        if ( i != pd_idx && i != qd_idx && sh->dev[i].towrite ) {
                                chosen = sh->dev[i].towrite;
                                sh->dev[i].towrite = NULL;

                                if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                                        wake_up(&conf->wait_for_overlap);

                                BUG_ON(sh->dev[i].written);
                                sh->dev[i].written = chosen;
                        }
                break;
        case CHECK_PARITY:
                BUG();          /* Not implemented yet */
        }

        for (i = disks; i--;)
                if (sh->dev[i].written) {
                        sector_t sector = sh->dev[i].sector;
                        struct bio *wbi = sh->dev[i].written;
                        while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
                                copy_data(1, wbi, sh->dev[i].page, sector);
                                wbi = r5_next_bio(wbi, sector);
                        }

                        set_bit(R5_LOCKED, &sh->dev[i].flags);
                        set_bit(R5_UPTODATE, &sh->dev[i].flags);
                }

        /* Note that unlike RAID-5, the ordering of the disks matters greatly.*/

        for (i = 0; i < disks; i++)
                ptrs[i] = (void *)raid6_empty_zero_page;

        count = 0;
        i = d0_idx;
        do {
                int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);

                ptrs[slot] = page_address(sh->dev[i].page);
                if (slot < syndrome_disks &&
                    !test_bit(R5_UPTODATE, &sh->dev[i].flags)) {
                        printk(KERN_ERR "block %d/%d not uptodate "
                               "on parity calc\n", i, count);
                        BUG();
                }

                i = raid6_next_disk(i, disks);
        } while (i != d0_idx);
        BUG_ON(count != syndrome_disks);

        raid6_call.gen_syndrome(syndrome_disks+2, STRIPE_SIZE, ptrs);

        switch(method) {
        case RECONSTRUCT_WRITE:
                set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
                set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
                set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
                set_bit(R5_LOCKED,   &sh->dev[qd_idx].flags);
                break;
        case UPDATE_PARITY:
                set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
                set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
                break;
        }
}


/* Compute one missing block */
static void compute_block_1(struct stripe_head *sh, int dd_idx, int nozero)
{
        int i, count, disks = sh->disks;
        void *ptr[MAX_XOR_BLOCKS], *dest, *p;
        int qd_idx = sh->qd_idx;

        pr_debug("compute_block_1, stripe %llu, idx %d\n",
                (unsigned long long)sh->sector, dd_idx);

        if ( dd_idx == qd_idx ) {
                /* We're actually computing the Q drive */
                compute_parity6(sh, UPDATE_PARITY);
        } else {
                dest = page_address(sh->dev[dd_idx].page);
                if (!nozero) memset(dest, 0, STRIPE_SIZE);
                count = 0;
                for (i = disks ; i--; ) {
                        if (i == dd_idx || i == qd_idx)
                                continue;
                        p = page_address(sh->dev[i].page);
                        if (test_bit(R5_UPTODATE, &sh->dev[i].flags))
                                ptr[count++] = p;
                        else
                                printk("compute_block() %d, stripe %llu, %d"
                                       " not present\n", dd_idx,
                                       (unsigned long long)sh->sector, i);

                        check_xor();
                }
                if (count)
                        xor_blocks(count, STRIPE_SIZE, dest, ptr);
                if (!nozero) set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
                else clear_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
        }
}

/* Compute two missing blocks */
static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
{
        int i, count, disks = sh->disks;
        int syndrome_disks = sh->ddf_layout ? disks : disks-2;
        int d0_idx = raid6_d0(sh);
        int faila = -1, failb = -1;
        /**** FIX THIS: This could be very bad if disks is close to 256 ****/
        void *ptrs[syndrome_disks+2];

        for (i = 0; i < disks ; i++)
                ptrs[i] = (void *)raid6_empty_zero_page;
        count = 0;
        i = d0_idx;
        do {
                int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);

                ptrs[slot] = page_address(sh->dev[i].page);

                if (i == dd_idx1)
                        faila = slot;
                if (i == dd_idx2)
                        failb = slot;
                i = raid6_next_disk(i, disks);
        } while (i != d0_idx);
        BUG_ON(count != syndrome_disks);

        BUG_ON(faila == failb);
        if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }

        pr_debug("compute_block_2, stripe %llu, idx %d,%d (%d,%d)\n",
                 (unsigned long long)sh->sector, dd_idx1, dd_idx2,
                 faila, failb);

        if (failb == syndrome_disks+1) {
                /* Q disk is one of the missing disks */
                if (faila == syndrome_disks) {
                        /* Missing P+Q, just recompute */
                        compute_parity6(sh, UPDATE_PARITY);
                        return;
                } else {
                        /* We're missing D+Q; recompute D from P */
                        compute_block_1(sh, ((dd_idx1 == sh->qd_idx) ?
                                             dd_idx2 : dd_idx1),
                                        0);
                        compute_parity6(sh, UPDATE_PARITY); /* Is this necessary? */
                        return;
                }
        }

        /* We're missing D+P or D+D; */
        if (failb == syndrome_disks) {
                /* We're missing D+P. */
                raid6_datap_recov(syndrome_disks+2, STRIPE_SIZE, faila, ptrs);
        } else {
                /* We're missing D+D. */
                raid6_2data_recov(syndrome_disks+2, STRIPE_SIZE, faila, failb,
                                  ptrs);
        }

        /* Both the above update both missing blocks */
        set_bit(R5_UPTODATE, &sh->dev[dd_idx1].flags);
        set_bit(R5_UPTODATE, &sh->dev[dd_idx2].flags);
}

static void
schedule_reconstruction5(struct stripe_head *sh, struct stripe_head_state *s,
                         int rcw, int expand)
{
        int i, pd_idx = sh->pd_idx, disks = sh->disks;

        if (rcw) {
                /* if we are not expanding this is a proper write request, and
                 * there will be bios with new data to be drained into the
                 * stripe cache
                 */
                if (!expand) {
                        sh->reconstruct_state = reconstruct_state_drain_run;
                        set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
                } else
                        sh->reconstruct_state = reconstruct_state_run;

                set_bit(STRIPE_OP_POSTXOR, &s->ops_request);

                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];

                        if (dev->towrite) {
                                set_bit(R5_LOCKED, &dev->flags);
                                set_bit(R5_Wantdrain, &dev->flags);
                                if (!expand)
                                        clear_bit(R5_UPTODATE, &dev->flags);
                                s->locked++;
                        }
                }
                if (s->locked + 1 == disks)
                        if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
                                atomic_inc(&sh->raid_conf->pending_full_writes);
        } else {
                BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||
                        test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));

                sh->reconstruct_state = reconstruct_state_prexor_drain_run;
                set_bit(STRIPE_OP_PREXOR, &s->ops_request);
                set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
                set_bit(STRIPE_OP_POSTXOR, &s->ops_request);

                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (i == pd_idx)
                                continue;

                        if (dev->towrite &&
                            (test_bit(R5_UPTODATE, &dev->flags) ||
                             test_bit(R5_Wantcompute, &dev->flags))) {
                                set_bit(R5_Wantdrain, &dev->flags);
                                set_bit(R5_LOCKED, &dev->flags);
                                clear_bit(R5_UPTODATE, &dev->flags);
                                s->locked++;
                        }
                }
        }

        /* keep the parity disk locked while asynchronous operations
         * are in flight
         */
        set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);
        clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
        s->locked++;

        pr_debug("%s: stripe %llu locked: %d ops_request: %lx\n",
                __func__, (unsigned long long)sh->sector,
                s->locked, s->ops_request);
}

/*
 * Each stripe/dev can have one or more bion attached.
 * toread/towrite point to the first in a chain.
 * The bi_next chain must be in order.
 */
static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
{
        struct bio **bip;
        raid5_conf_t *conf = sh->raid_conf;
        int firstwrite=0;

        pr_debug("adding bh b#%llu to stripe s#%llu\n",
                (unsigned long long)bi->bi_sector,
                (unsigned long long)sh->sector);


        spin_lock(&sh->lock);
        spin_lock_irq(&conf->device_lock);
        if (forwrite) {
                bip = &sh->dev[dd_idx].towrite;
                if (*bip == NULL && sh->dev[dd_idx].written == NULL)
                        firstwrite = 1;
        } else
                bip = &sh->dev[dd_idx].toread;
        while (*bip && (*bip)->bi_sector < bi->bi_sector) {
                if ((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector)
                        goto overlap;
                bip = & (*bip)->bi_next;
        }
        if (*bip && (*bip)->bi_sector < bi->bi_sector + ((bi->bi_size)>>9))
                goto overlap;

        BUG_ON(*bip && bi->bi_next && (*bip) != bi->bi_next);
        if (*bip)
                bi->bi_next = *bip;
        *bip = bi;
        bi->bi_phys_segments++;
        spin_unlock_irq(&conf->device_lock);
        spin_unlock(&sh->lock);

        pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
                (unsigned long long)bi->bi_sector,
                (unsigned long long)sh->sector, dd_idx);

        if (conf->mddev->bitmap && firstwrite) {
                bitmap_startwrite(conf->mddev->bitmap, sh->sector,
                                  STRIPE_SECTORS, 0);
                sh->bm_seq = conf->seq_flush+1;
                set_bit(STRIPE_BIT_DELAY, &sh->state);
        }

        if (forwrite) {
                /* check if page is covered */
                sector_t sector = sh->dev[dd_idx].sector;
                for (bi=sh->dev[dd_idx].towrite;
                     sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
                             bi && bi->bi_sector <= sector;
                     bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
                        if (bi->bi_sector + (bi->bi_size>>9) >= sector)
                                sector = bi->bi_sector + (bi->bi_size>>9);
                }
                if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
                        set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
        }
        return 1;

 overlap:
        set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
        spin_unlock_irq(&conf->device_lock);
        spin_unlock(&sh->lock);
        return 0;
}

static void end_reshape(raid5_conf_t *conf);

static int page_is_zero(struct page *p)
{
        char *a = page_address(p);
        return ((*(u32*)a) == 0 &&
                memcmp(a, a+4, STRIPE_SIZE-4)==0);
}

static void stripe_set_idx(sector_t stripe, raid5_conf_t *conf, int previous,
                            struct stripe_head *sh)
{
        int sectors_per_chunk =
                previous ? (conf->prev_chunk >> 9)
                         : (conf->chunk_size >> 9);
        int dd_idx;
        int chunk_offset = sector_div(stripe, sectors_per_chunk);
        int disks = previous ? conf->previous_raid_disks : conf->raid_disks;

        raid5_compute_sector(conf,
                             stripe * (disks - conf->max_degraded)
                             *sectors_per_chunk + chunk_offset,
                             previous,
                             &dd_idx, sh);
}

static void
handle_failed_stripe(raid5_conf_t *conf, struct stripe_head *sh,
                                struct stripe_head_state *s, int disks,
                                struct bio **return_bi)
{
        int i;
        for (i = disks; i--; ) {
                struct bio *bi;
                int bitmap_end = 0;

                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        mdk_rdev_t *rdev;
                        rcu_read_lock();
                        rdev = rcu_dereference(conf->disks[i].rdev);
                        if (rdev && test_bit(In_sync, &rdev->flags))
                                /* multiple read failures in one stripe */
                                md_error(conf->mddev, rdev);
                        rcu_read_unlock();
                }
                spin_lock_irq(&conf->device_lock);
                /* fail all writes first */
                bi = sh->dev[i].towrite;
                sh->dev[i].towrite = NULL;
                if (bi) {
                        s->to_write--;
                        bitmap_end = 1;
                }

                if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                        wake_up(&conf->wait_for_overlap);

                while (bi && bi->bi_sector <
                        sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
                        if (!raid5_dec_bi_phys_segments(bi)) {
                                md_write_end(conf->mddev);
                                bi->bi_next = *return_bi;
                                *return_bi = bi;
                        }
                        bi = nextbi;
                }
                /* and fail all 'written' */
                bi = sh->dev[i].written;
                sh->dev[i].written = NULL;
                if (bi) bitmap_end = 1;
                while (bi && bi->bi_sector <
                       sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
                        if (!raid5_dec_bi_phys_segments(bi)) {
                                md_write_end(conf->mddev);
                                bi->bi_next = *return_bi;
                                *return_bi = bi;
                        }
                        bi = bi2;
                }

                /* fail any reads if this device is non-operational and
                 * the data has not reached the cache yet.
                 */
                if (!test_bit(R5_Wantfill, &sh->dev[i].flags) &&
                    (!test_bit(R5_Insync, &sh->dev[i].flags) ||
                      test_bit(R5_ReadError, &sh->dev[i].flags))) {
                        bi = sh->dev[i].toread;
                        sh->dev[i].toread = NULL;
                        if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                                wake_up(&conf->wait_for_overlap);
                        if (bi) s->to_read--;
                        while (bi && bi->bi_sector <
                               sh->dev[i].sector + STRIPE_SECTORS) {
                                struct bio *nextbi =
                                        r5_next_bio(bi, sh->dev[i].sector);
                                clear_bit(BIO_UPTODATE, &bi->bi_flags);
                                if (!raid5_dec_bi_phys_segments(bi)) {
                                        bi->bi_next = *return_bi;
                                        *return_bi = bi;
                                }
                                bi = nextbi;
                        }
                }
                spin_unlock_irq(&conf->device_lock);
                if (bitmap_end)
                        bitmap_endwrite(conf->mddev->bitmap, sh->sector,
                                        STRIPE_SECTORS, 0, 0);
        }

        if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
                if (atomic_dec_and_test(&conf->pending_full_writes))
                        md_wakeup_thread(conf->mddev->thread);
}

/* fetch_block5 - checks the given member device to see if its data needs
 * to be read or computed to satisfy a request.
 *
 * Returns 1 when no more member devices need to be checked, otherwise returns
 * 0 to tell the loop in handle_stripe_fill5 to continue
 */
static int fetch_block5(struct stripe_head *sh, struct stripe_head_state *s,
                        int disk_idx, int disks)
{
        struct r5dev *dev = &sh->dev[disk_idx];
        struct r5dev *failed_dev = &sh->dev[s->failed_num];

        /* is the data in this block needed, and can we get it? */
        if (!test_bit(R5_LOCKED, &dev->flags) &&
            !test_bit(R5_UPTODATE, &dev->flags) &&
            (dev->toread ||
             (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
             s->syncing || s->expanding ||
             (s->failed &&
              (failed_dev->toread ||
               (failed_dev->towrite &&
                !test_bit(R5_OVERWRITE, &failed_dev->flags)))))) {
                /* We would like to get this block, possibly by computing it,
                 * otherwise read it if the backing disk is insync
                 */
                if ((s->uptodate == disks - 1) &&
                    (s->failed && disk_idx == s->failed_num)) {
                        set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                        set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                        set_bit(R5_Wantcompute, &dev->flags);
                        sh->ops.target = disk_idx;
                        s->req_compute = 1;
                        /* Careful: from this point on 'uptodate' is in the eye
                         * of raid5_run_ops which services 'compute' operations
                         * before writes. R5_Wantcompute flags a block that will
                         * be R5_UPTODATE by the time it is needed for a
                         * subsequent operation.
                         */
                        s->uptodate++;
                        return 1; /* uptodate + compute == disks */
                } else if (test_bit(R5_Insync, &dev->flags)) {
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantread, &dev->flags);
                        s->locked++;
                        pr_debug("Reading block %d (sync=%d)\n", disk_idx,
                                s->syncing);
                }
        }

        return 0;
}

/**
 * handle_stripe_fill5 - read or compute data to satisfy pending requests.
 */
static void handle_stripe_fill5(struct stripe_head *sh,
                        struct stripe_head_state *s, int disks)
{
        int i;

        /* look for blocks to read/compute, skip this if a compute
         * is already in flight, or if the stripe contents are in the
         * midst of changing due to a write
         */
        if (!test_bit(STRIPE_COMPUTE_RUN, &sh->state) && !sh->check_state &&
            !sh->reconstruct_state)
                for (i = disks; i--; )
                        if (fetch_block5(sh, s, i, disks))
                                break;
        set_bit(STRIPE_HANDLE, &sh->state);
}

static void handle_stripe_fill6(struct stripe_head *sh,
                        struct stripe_head_state *s, struct r6_state *r6s,
                        int disks)
{
        int i;
        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (!test_bit(R5_LOCKED, &dev->flags) &&
                    !test_bit(R5_UPTODATE, &dev->flags) &&
                    (dev->toread || (dev->towrite &&
                     !test_bit(R5_OVERWRITE, &dev->flags)) ||
                     s->syncing || s->expanding ||
                     (s->failed >= 1 &&
                      (sh->dev[r6s->failed_num[0]].toread ||
                       s->to_write)) ||
                     (s->failed >= 2 &&
                      (sh->dev[r6s->failed_num[1]].toread ||
                       s->to_write)))) {
                        /* we would like to get this block, possibly
                         * by computing it, but we might not be able to
                         */
                        if ((s->uptodate == disks - 1) &&
                            (s->failed && (i == r6s->failed_num[0] ||
                                           i == r6s->failed_num[1]))) {
                                pr_debug("Computing stripe %llu block %d\n",
                                       (unsigned long long)sh->sector, i);
                                compute_block_1(sh, i, 0);
                                s->uptodate++;
                        } else if ( s->uptodate == disks-2 && s->failed >= 2 ) {
                                /* Computing 2-failure is *very* expensive; only
                                 * do it if failed >= 2
                                 */
                                int other;
                                for (other = disks; other--; ) {
                                        if (other == i)
                                                continue;
                                        if (!test_bit(R5_UPTODATE,
                                              &sh->dev[other].flags))
                                                break;
                                }
                                BUG_ON(other < 0);
                                pr_debug("Computing stripe %llu blocks %d,%d\n",
                                       (unsigned long long)sh->sector,
                                       i, other);
                                compute_block_2(sh, i, other);
                                s->uptodate += 2;
                        } else if (test_bit(R5_Insync, &dev->flags)) {
                                set_bit(R5_LOCKED, &dev->flags);
                                set_bit(R5_Wantread, &dev->flags);
                                s->locked++;
                                pr_debug("Reading block %d (sync=%d)\n",
                                        i, s->syncing);
                        }
                }
        }
        set_bit(STRIPE_HANDLE, &sh->state);
}


/* handle_stripe_clean_event
 * any written block on an uptodate or failed drive can be returned.
 * Note that if we 'wrote' to a failed drive, it will be UPTODATE, but
 * never LOCKED, so we don't need to test 'failed' directly.
 */
static void handle_stripe_clean_event(raid5_conf_t *conf,
        struct stripe_head *sh, int disks, struct bio **return_bi)
{
        int i;
        struct r5dev *dev;

        for (i = disks; i--; )
                if (sh->dev[i].written) {
                        dev = &sh->dev[i];
                        if (!test_bit(R5_LOCKED, &dev->flags) &&
                                test_bit(R5_UPTODATE, &dev->flags)) {
                                /* We can return any write requests */
                                struct bio *wbi, *wbi2;
                                int bitmap_end = 0;
                                pr_debug("Return write for disc %d\n", i);
                                spin_lock_irq(&conf->device_lock);
                                wbi = dev->written;
                                dev->written = NULL;
                                while (wbi && wbi->bi_sector <
                                        dev->sector + STRIPE_SECTORS) {
                                        wbi2 = r5_next_bio(wbi, dev->sector);
                                        if (!raid5_dec_bi_phys_segments(wbi)) {
                                                md_write_end(conf->mddev);
                                                wbi->bi_next = *return_bi;
                                                *return_bi = wbi;
                                        }
                                        wbi = wbi2;
                                }
                                if (dev->towrite == NULL)
                                        bitmap_end = 1;
                                spin_unlock_irq(&conf->device_lock);
                                if (bitmap_end)
                                        bitmap_endwrite(conf->mddev->bitmap,
                                                        sh->sector,
                                                        STRIPE_SECTORS,
                                         !test_bit(STRIPE_DEGRADED, &sh->state),
                                                        0);
                        }
                }

        if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
                if (atomic_dec_and_test(&conf->pending_full_writes))
                        md_wakeup_thread(conf->mddev->thread);
}

static void handle_stripe_dirtying5(raid5_conf_t *conf,
                struct stripe_head *sh, struct stripe_head_state *s, int disks)
{
        int rmw = 0, rcw = 0, i;
        for (i = disks; i--; ) {
                /* would I have to read this buffer for read_modify_write */
                struct r5dev *dev = &sh->dev[i];
                if ((dev->towrite || i == sh->pd_idx) &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
                      test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags))
                                rmw++;
                        else
                                rmw += 2*disks;  /* cannot read it */
                }
                /* Would I have to read this buffer for reconstruct_write */
                if (!test_bit(R5_OVERWRITE, &dev->flags) && i != sh->pd_idx &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
                    test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags)) rcw++;
                        else
                                rcw += 2*disks;
                }
        }
        pr_debug("for sector %llu, rmw=%d rcw=%d\n",
                (unsigned long long)sh->sector, rmw, rcw);
        set_bit(STRIPE_HANDLE, &sh->state);
        if (rmw < rcw && rmw > 0)
                /* prefer read-modify-write, but need to get some data */
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if ((dev->towrite || i == sh->pd_idx) &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
                            test_bit(R5_Wantcompute, &dev->flags)) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (
                                  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                        pr_debug("Read_old block "
                                                "%d for r-m-w\n", i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        s->locked++;
                                } else {
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        if (rcw <= rmw && rcw > 0)
                /* want reconstruct write, but need to get some data */
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (!test_bit(R5_OVERWRITE, &dev->flags) &&
                            i != sh->pd_idx &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
                            test_bit(R5_Wantcompute, &dev->flags)) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (
                                  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                        pr_debug("Read_old block "
                                                "%d for Reconstruct\n", i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        s->locked++;
                                } else {
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        /* now if nothing is locked, and if we have enough data,
         * we can start a write request
         */
        /* since handle_stripe can be called at any time we need to handle the
         * case where a compute block operation has been submitted and then a
         * subsequent call wants to start a write request.  raid5_run_ops only
         * handles the case where compute block and postxor are requested
         * simultaneously.  If this is not the case then new writes need to be
         * held off until the compute completes.
         */
        if ((s->req_compute || !test_bit(STRIPE_COMPUTE_RUN, &sh->state)) &&
            (s->locked == 0 && (rcw == 0 || rmw == 0) &&
            !test_bit(STRIPE_BIT_DELAY, &sh->state)))
                schedule_reconstruction5(sh, s, rcw == 0, 0);
}

static void handle_stripe_dirtying6(raid5_conf_t *conf,
                struct stripe_head *sh, struct stripe_head_state *s,
                struct r6_state *r6s, int disks)
{
        int rcw = 0, must_compute = 0, pd_idx = sh->pd_idx, i;
        int qd_idx = sh->qd_idx;
        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                /* Would I have to read this buffer for reconstruct_write */
                if (!test_bit(R5_OVERWRITE, &dev->flags)
                    && i != pd_idx && i != qd_idx
                    && (!test_bit(R5_LOCKED, &dev->flags)
                            ) &&
                    !test_bit(R5_UPTODATE, &dev->flags)) {
                        if (test_bit(R5_Insync, &dev->flags)) rcw++;
                        else {
                                pr_debug("raid6: must_compute: "
                                        "disk %d flags=%#lx\n", i, dev->flags);
                                must_compute++;
                        }
                }
        }
        pr_debug("for sector %llu, rcw=%d, must_compute=%d\n",
               (unsigned long long)sh->sector, rcw, must_compute);
        set_bit(STRIPE_HANDLE, &sh->state);

        if (rcw > 0)
                /* want reconstruct write, but need to get some data */
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (!test_bit(R5_OVERWRITE, &dev->flags)
                            && !(s->failed == 0 && (i == pd_idx || i == qd_idx))
                            && !test_bit(R5_LOCKED, &dev->flags) &&
                            !test_bit(R5_UPTODATE, &dev->flags) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (
                                  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                        pr_debug("Read_old stripe %llu "
                                                "block %d for Reconstruct\n",
                                             (unsigned long long)sh->sector, i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        s->locked++;
                                } else {
                                        pr_debug("Request delayed stripe %llu "
                                                "block %d for Reconstruct\n",
                                             (unsigned long long)sh->sector, i);
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        /* now if nothing is locked, and if we have enough data, we can start a
         * write request
         */
        if (s->locked == 0 && rcw == 0 &&
            !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
                if (must_compute > 0) {
                        /* We have failed blocks and need to compute them */
                        switch (s->failed) {
                        case 0:
                                BUG();
                        case 1:
                                compute_block_1(sh, r6s->failed_num[0], 0);
                                break;
                        case 2:
                                compute_block_2(sh, r6s->failed_num[0],
                                                r6s->failed_num[1]);
                                break;
                        default: /* This request should have been failed? */
                                BUG();
                        }
                }

                pr_debug("Computing parity for stripe %llu\n",
                        (unsigned long long)sh->sector);
                compute_parity6(sh, RECONSTRUCT_WRITE);
                /* now every locked buffer is ready to be written */
                for (i = disks; i--; )
                        if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
                                pr_debug("Writing stripe %llu block %d\n",
                                       (unsigned long long)sh->sector, i);
                                s->locked++;
                                set_bit(R5_Wantwrite, &sh->dev[i].flags);
                        }
                if (s->locked == disks)
                        if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
                                atomic_inc(&conf->pending_full_writes);
                /* after a RECONSTRUCT_WRITE, the stripe MUST be in-sync */
                set_bit(STRIPE_INSYNC, &sh->state);

                if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                        atomic_dec(&conf->preread_active_stripes);
                        if (atomic_read(&conf->preread_active_stripes) <
                            IO_THRESHOLD)
                                md_wakeup_thread(conf->mddev->thread);
                }
        }
}

static void handle_parity_checks5(raid5_conf_t *conf, struct stripe_head *sh,
                                struct stripe_head_state *s, int disks)
{
        struct r5dev *dev = NULL;

        set_bit(STRIPE_HANDLE, &sh->state);

        switch (sh->check_state) {
        case check_state_idle:
                /* start a new check operation if there are no failures */
                if (s->failed == 0) {
                        BUG_ON(s->uptodate != disks);
                        sh->check_state = check_state_run;
                        set_bit(STRIPE_OP_CHECK, &s->ops_request);
                        clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
                        s->uptodate--;
                        break;
                }
                dev = &sh->dev[s->failed_num];
                /* fall through */
        case check_state_compute_result:
                sh->check_state = check_state_idle;
                if (!dev)
                        dev = &sh->dev[sh->pd_idx];

                /* check that a write has not made the stripe insync */
                if (test_bit(STRIPE_INSYNC, &sh->state))
                        break;

                /* either failed parity check, or recovery is happening */
                BUG_ON(!test_bit(R5_UPTODATE, &dev->flags));
                BUG_ON(s->uptodate != disks);

                set_bit(R5_LOCKED, &dev->flags);
                s->locked++;
                set_bit(R5_Wantwrite, &dev->flags);

                clear_bit(STRIPE_DEGRADED, &sh->state);
                set_bit(STRIPE_INSYNC, &sh->state);
                break;
        case check_state_run:
                break; /* we will be called again upon completion */
        case check_state_check_result:
                sh->check_state = check_state_idle;

                /* if a failure occurred during the check operation, leave
                 * STRIPE_INSYNC not set and let the stripe be handled again
                 */
                if (s->failed)
                        break;

                /* handle a successful check operation, if parity is correct
                 * we are done.  Otherwise update the mismatch count and repair
                 * parity if !MD_RECOVERY_CHECK
                 */
                if (sh->ops.zero_sum_result == 0)
                        /* parity is correct (on disc,
                         * not in buffer any more)
                         */
                        set_bit(STRIPE_INSYNC, &sh->state);
                else {
                        conf->mddev->resync_mismatches += STRIPE_SECTORS;
                        if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                                /* don't try to repair!! */
                                set_bit(STRIPE_INSYNC, &sh->state);
                        else {
                                sh->check_state = check_state_compute_run;
                                set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                                set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                                set_bit(R5_Wantcompute,
                                        &sh->dev[sh->pd_idx].flags);
                                sh->ops.target = sh->pd_idx;
                                s->uptodate++;
                        }
                }
                break;
        case check_state_compute_run:
                break;
        default:
                printk(KERN_ERR "%s: unknown check_state: %d sector: %llu\n",
                       __func__, sh->check_state,
                       (unsigned long long) sh->sector);
                BUG();
        }
}


static void handle_parity_checks6(raid5_conf_t *conf, struct stripe_head *sh,
                                struct stripe_head_state *s,
                                struct r6_state *r6s, struct page *tmp_page,
                                int disks)
{
        int update_p = 0, update_q = 0;
        struct r5dev *dev;
        int pd_idx = sh->pd_idx;
        int qd_idx = sh->qd_idx;

        set_bit(STRIPE_HANDLE, &sh->state);

        BUG_ON(s->failed > 2);
        BUG_ON(s->uptodate < disks);
        /* Want to check and possibly repair P and Q.
         * However there could be one 'failed' device, in which
         * case we can only check one of them, possibly using the
         * other to generate missing data
         */

        /* If !tmp_page, we cannot do the calculations,
         * but as we have set STRIPE_HANDLE, we will soon be called
         * by stripe_handle with a tmp_page - just wait until then.
         */
        if (tmp_page) {
                if (s->failed == r6s->q_failed) {
                        /* The only possible failed device holds 'Q', so it
                         * makes sense to check P (If anything else were failed,
                         * we would have used P to recreate it).
                         */
                        compute_block_1(sh, pd_idx, 1);
                        if (!page_is_zero(sh->dev[pd_idx].page)) {
                                compute_block_1(sh, pd_idx, 0);
                                update_p = 1;
                        }
                }
                if (!r6s->q_failed && s->failed < 2) {
                        /* q is not failed, and we didn't use it to generate
                         * anything, so it makes sense to check it
                         */
                        memcpy(page_address(tmp_page),
                               page_address(sh->dev[qd_idx].page),
                               STRIPE_SIZE);
                        compute_parity6(sh, UPDATE_PARITY);
                        if (memcmp(page_address(tmp_page),
                                   page_address(sh->dev[qd_idx].page),
                                   STRIPE_SIZE) != 0) {
                                clear_bit(STRIPE_INSYNC, &sh->state);
                                update_q = 1;
                        }
                }
                if (update_p || update_q) {
                        conf->mddev->resync_mismatches += STRIPE_SECTORS;
                        if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                                /* don't try to repair!! */
                                update_p = update_q = 0;
                }

                /* now write out any block on a failed drive,
                 * or P or Q if they need it
                 */

                if (s->failed == 2) {
                        dev = &sh->dev[r6s->failed_num[1]];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (s->failed >= 1) {
                        dev = &sh->dev[r6s->failed_num[0]];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }

                if (update_p) {
                        dev = &sh->dev[pd_idx];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (update_q) {
                        dev = &sh->dev[qd_idx];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                clear_bit(STRIPE_DEGRADED, &sh->state);

                set_bit(STRIPE_INSYNC, &sh->state);
        }
}

static void handle_stripe_expansion(raid5_conf_t *conf, struct stripe_head *sh,
                                struct r6_state *r6s)
{
        int i;

        /* We have read all the blocks in this stripe and now we need to
         * copy some of them into a target stripe for expand.
         */
        struct dma_async_tx_descriptor *tx = NULL;
        clear_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        for (i = 0; i < sh->disks; i++)
                if (i != sh->pd_idx && i != sh->qd_idx) {
                        int dd_idx, j;
                        struct stripe_head *sh2;

                        sector_t bn = compute_blocknr(sh, i, 1);
                        sector_t s = raid5_compute_sector(conf, bn, 0,
                                                          &dd_idx, NULL);
                        sh2 = get_active_stripe(conf, s, 0, 1);
                        if (sh2 == NULL)
                                /* so far only the early blocks of this stripe
                                 * have been requested.  When later blocks
                                 * get requested, we will try again
                                 */
                                continue;
                        if (!test_bit(STRIPE_EXPANDING, &sh2->state) ||
                           test_bit(R5_Expanded, &sh2->dev[dd_idx].flags)) {
                                /* must have already done this block */
                                release_stripe(sh2);
                                continue;
                        }

                        /* place all the copies on one channel */
                        tx = async_memcpy(sh2->dev[dd_idx].page,
                                sh->dev[i].page, 0, 0, STRIPE_SIZE,
                                ASYNC_TX_DEP_ACK, tx, NULL, NULL);

                        set_bit(R5_Expanded, &sh2->dev[dd_idx].flags);
                        set_bit(R5_UPTODATE, &sh2->dev[dd_idx].flags);
                        for (j = 0; j < conf->raid_disks; j++)
                                if (j != sh2->pd_idx &&
                                    (!r6s || j != sh2->qd_idx) &&
                                    !test_bit(R5_Expanded, &sh2->dev[j].flags))
                                        break;
                        if (j == conf->raid_disks) {
                                set_bit(STRIPE_EXPAND_READY, &sh2->state);
                                set_bit(STRIPE_HANDLE, &sh2->state);
                        }
                        release_stripe(sh2);

                }
        /* done submitting copies, wait for them to complete */
        if (tx) {
                async_tx_ack(tx);
                dma_wait_for_async_tx(tx);
        }
}


/*
 * handle_stripe - do things to a stripe.
 *
 * We lock the stripe and then examine the state of various bits
 * to see what needs to be done.
 * Possible results:
 *    return some read request which now have data
 *    return some write requests which are safely on disc
 *    schedule a read on some buffers
 *    schedule a write of some buffers
 *    return confirmation of parity correctness
 *
 * buffers are taken off read_list or write_list, and bh_cache buffers
 * get BH_Lock set before the stripe lock is released.
 *
 */

static bool handle_stripe5(struct stripe_head *sh)
{
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks, i;
        struct bio *return_bi = NULL;
        struct stripe_head_state s;
        struct r5dev *dev;
        mdk_rdev_t *blocked_rdev = NULL;
        int prexor;

        memset(&s, 0, sizeof(s));
        pr_debug("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d check:%d "
                 "reconstruct:%d\n", (unsigned long long)sh->sector, sh->state,
                 atomic_read(&sh->count), sh->pd_idx, sh->check_state,
                 sh->reconstruct_state);

        spin_lock(&sh->lock);
        clear_bit(STRIPE_HANDLE, &sh->state);
        clear_bit(STRIPE_DELAYED, &sh->state);

        s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
        s.expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        s.expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);

        /* Now to look around and see what can be done */
        rcu_read_lock();
        for (i=disks; i--; ) {
                mdk_rdev_t *rdev;
                struct r5dev *dev = &sh->dev[i];
                clear_bit(R5_Insync, &dev->flags);

                pr_debug("check %d: state 0x%lx toread %p read %p write %p "
                        "written %p\n", i, dev->flags, dev->toread, dev->read,
                        dev->towrite, dev->written);

                /* maybe we can request a biofill operation
                 *
                 * new wantfill requests are only permitted while
                 * ops_complete_biofill is guaranteed to be inactive
                 */
                if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread &&
                    !test_bit(STRIPE_BIOFILL_RUN, &sh->state))
                        set_bit(R5_Wantfill, &dev->flags);

                /* now count some things */
                if (test_bit(R5_LOCKED, &dev->flags)) s.locked++;
                if (test_bit(R5_UPTODATE, &dev->flags)) s.uptodate++;
                if (test_bit(R5_Wantcompute, &dev->flags)) s.compute++;

                if (test_bit(R5_Wantfill, &dev->flags))
                        s.to_fill++;
                else if (dev->toread)
                        s.to_read++;
                if (dev->towrite) {
                        s.to_write++;
                        if (!test_bit(R5_OVERWRITE, &dev->flags))
                                s.non_overwrite++;
                }
                if (dev->written)
                        s.written++;
                rdev = rcu_dereference(conf->disks[i].rdev);
                if (blocked_rdev == NULL &&
                    rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
                        blocked_rdev = rdev;
                        atomic_inc(&rdev->nr_pending);
                }
                if (!rdev || !test_bit(In_sync, &rdev->flags)) {
                        /* The ReadError flag will just be confusing now */
                        clear_bit(R5_ReadError, &dev->flags);
                        clear_bit(R5_ReWrite, &dev->flags);
                }
                if (!rdev || !test_bit(In_sync, &rdev->flags)
                    || test_bit(R5_ReadError, &dev->flags)) {
                        s.failed++;
                        s.failed_num = i;
                } else
                        set_bit(R5_Insync, &dev->flags);
        }
        rcu_read_unlock();

        if (unlikely(blocked_rdev)) {
                if (s.syncing || s.expanding || s.expanded ||
                    s.to_write || s.written) {
                        set_bit(STRIPE_HANDLE, &sh->state);
                        goto unlock;
                }
                /* There is nothing for the blocked_rdev to block */
                rdev_dec_pending(blocked_rdev, conf->mddev);
                blocked_rdev = NULL;
        }

        if (s.to_fill && !test_bit(STRIPE_BIOFILL_RUN, &sh->state)) {
                set_bit(STRIPE_OP_BIOFILL, &s.ops_request);
                set_bit(STRIPE_BIOFILL_RUN, &sh->state);
        }

        pr_debug("locked=%d uptodate=%d to_read=%d"
                " to_write=%d failed=%d failed_num=%d\n",
                s.locked, s.uptodate, s.to_read, s.to_write,
                s.failed, s.failed_num);
        /* check if the array has lost two devices and, if so, some requests might
         * need to be failed
         */
        if (s.failed > 1 && s.to_read+s.to_write+s.written)
                handle_failed_stripe(conf, sh, &s, disks, &return_bi);
        if (s.failed > 1 && s.syncing) {
                md_done_sync(conf->mddev, STRIPE_SECTORS,0);
                clear_bit(STRIPE_SYNCING, &sh->state);
                s.syncing = 0;
        }

        /* might be able to return some write requests if the parity block
         * is safe, or on a failed drive
         */
        dev = &sh->dev[sh->pd_idx];
        if ( s.written &&
             ((test_bit(R5_Insync, &dev->flags) &&
               !test_bit(R5_LOCKED, &dev->flags) &&
               test_bit(R5_UPTODATE, &dev->flags)) ||
               (s.failed == 1 && s.failed_num == sh->pd_idx)))
                handle_stripe_clean_event(conf, sh, disks, &return_bi);

        /* Now we might consider reading some blocks, either to check/generate
         * parity, or to satisfy requests
         * or to load a block that is being partially written.
         */
        if (s.to_read || s.non_overwrite ||
            (s.syncing && (s.uptodate + s.compute < disks)) || s.expanding)
                handle_stripe_fill5(sh, &s, disks);

        /* Now we check to see if any write operations have recently
         * completed
         */
        prexor = 0;
        if (sh->reconstruct_state == reconstruct_state_prexor_drain_result)
                prexor = 1;
        if (sh->reconstruct_state == reconstruct_state_drain_result ||
            sh->reconstruct_state == reconstruct_state_prexor_drain_result) {
                sh->reconstruct_state = reconstruct_state_idle;

                /* All the 'written' buffers and the parity block are ready to
                 * be written back to disk
                 */
                BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags));
                for (i = disks; i--; ) {
                        dev = &sh->dev[i];
                        if (test_bit(R5_LOCKED, &dev->flags) &&
                                (i == sh->pd_idx || dev->written)) {
                                pr_debug("Writing block %d\n", i);
                                set_bit(R5_Wantwrite, &dev->flags);
                                if (prexor)
                                        continue;
                                if (!test_bit(R5_Insync, &dev->flags) ||
                                    (i == sh->pd_idx && s.failed == 0))
                                        set_bit(STRIPE_INSYNC, &sh->state);
                        }
                }
                if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                        atomic_dec(&conf->preread_active_stripes);
                        if (atomic_read(&conf->preread_active_stripes) <
                                IO_THRESHOLD)
                                md_wakeup_thread(conf->mddev->thread);
                }
        }

        /* Now to consider new write requests and what else, if anything
         * should be read.  We do not handle new writes when:
         * 1/ A 'write' operation (copy+xor) is already in flight.
         * 2/ A 'check' operation is in flight, as it may clobber the parity
         *    block.
         */
        if (s.to_write && !sh->reconstruct_state && !sh->check_state)
                handle_stripe_dirtying5(conf, sh, &s, disks);

        /* maybe we need to check and possibly fix the parity for this stripe
         * Any reads will already have been scheduled, so we just see if enough
         * data is available.  The parity check is held off while parity
         * dependent operations are in flight.
         */
        if (sh->check_state ||
            (s.syncing && s.locked == 0 &&
             !test_bit(STRIPE_COMPUTE_RUN, &sh->state) &&
             !test_bit(STRIPE_INSYNC, &sh->state)))
                handle_parity_checks5(conf, sh, &s, disks);

        if (s.syncing && s.locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
                md_done_sync(conf->mddev, STRIPE_SECTORS,1);
                clear_bit(STRIPE_SYNCING, &sh->state);
        }

        /* If the failed drive is just a ReadError, then we might need to progress
         * the repair/check process
         */
        if (s.failed == 1 && !conf->mddev->ro &&
            test_bit(R5_ReadError, &sh->dev[s.failed_num].flags)
            && !test_bit(R5_LOCKED, &sh->dev[s.failed_num].flags)
            && test_bit(R5_UPTODATE, &sh->dev[s.failed_num].flags)
                ) {
                dev = &sh->dev[s.failed_num];
                if (!test_bit(R5_ReWrite, &dev->flags)) {
                        set_bit(R5_Wantwrite, &dev->flags);
                        set_bit(R5_ReWrite, &dev->flags);
                        set_bit(R5_LOCKED, &dev->flags);
                        s.locked++;
                } else {
                        /* let's read it back */
                        set_bit(R5_Wantread, &dev->flags);
                        set_bit(R5_LOCKED, &dev->flags);
                        s.locked++;
                }
        }

        /* Finish reconstruct operations initiated by the expansion process */
        if (sh->reconstruct_state == reconstruct_state_result) {
                struct stripe_head *sh2
                        = get_active_stripe(conf, sh->sector, 1, 1);
                if (sh2 && test_bit(STRIPE_EXPAND_SOURCE, &sh2->state)) {
                        /* sh cannot be written until sh2 has been read.
                         * so arrange for sh to be delayed a little
                         */
                        set_bit(STRIPE_DELAYED, &sh->state);
                        set_bit(STRIPE_HANDLE, &sh->state);
                        if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE,
                                              &sh2->state))
                                atomic_inc(&conf->preread_active_stripes);
                        release_stripe(sh2);
                        goto unlock;
                }
                if (sh2)
                        release_stripe(sh2);

                sh->reconstruct_state = reconstruct_state_idle;
                clear_bit(STRIPE_EXPANDING, &sh->state);
                for (i = conf->raid_disks; i--; ) {
                        set_bit(R5_Wantwrite, &sh->dev[i].flags);
                        set_bit(R5_LOCKED, &sh->dev[i].flags);
                        s.locked++;
                }
        }

        if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state) &&
            !sh->reconstruct_state) {
                /* Need to write out all blocks after computing parity */
                sh->disks = conf->raid_disks;
                stripe_set_idx(sh->sector, conf, 0, sh);
                schedule_reconstruction5(sh, &s, 1, 1);
        } else if (s.expanded && !sh->reconstruct_state && s.locked == 0) {
                clear_bit(STRIPE_EXPAND_READY, &sh->state);
                atomic_dec(&conf->reshape_stripes);
                wake_up(&conf->wait_for_overlap);
                md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
        }

        if (s.expanding && s.locked == 0 &&
            !test_bit(STRIPE_COMPUTE_RUN, &sh->state))
                handle_stripe_expansion(conf, sh, NULL);

 unlock:
        spin_unlock(&sh->lock);

        /* wait for this device to become unblocked */
        if (unlikely(blocked_rdev))
                md_wait_for_blocked_rdev(blocked_rdev, conf->mddev);

        if (s.ops_request)
                raid5_run_ops(sh, s.ops_request);

        ops_run_io(sh, &s);

        return_io(return_bi);

        return blocked_rdev == NULL;
}

static bool handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
{
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks;
        struct bio *return_bi = NULL;
        int i, pd_idx = sh->pd_idx, qd_idx = sh->qd_idx;
        struct stripe_head_state s;
        struct r6_state r6s;
        struct r5dev *dev, *pdev, *qdev;
        mdk_rdev_t *blocked_rdev = NULL;

        pr_debug("handling stripe %llu, state=%#lx cnt=%d, "
                "pd_idx=%d, qd_idx=%d\n",
               (unsigned long long)sh->sector, sh->state,
               atomic_read(&sh->count), pd_idx, qd_idx);
        memset(&s, 0, sizeof(s));

        spin_lock(&sh->lock);
        clear_bit(STRIPE_HANDLE, &sh->state);
        clear_bit(STRIPE_DELAYED, &sh->state);

        s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
        s.expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        s.expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);
        /* Now to look around and see what can be done */

        rcu_read_lock();
        for (i=disks; i--; ) {
                mdk_rdev_t *rdev;
                dev = &sh->dev[i];
                clear_bit(R5_Insync, &dev->flags);

                pr_debug("check %d: state 0x%lx read %p write %p written %p\n",
                        i, dev->flags, dev->toread, dev->towrite, dev->written);
                /* maybe we can reply to a read */
                if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
                        struct bio *rbi, *rbi2;
                        pr_debug("Return read for disc %d\n", i);
                        spin_lock_irq(&conf->device_lock);
                        rbi = dev->toread;
                        dev->toread = NULL;
                        if (test_and_clear_bit(R5_Overlap, &dev->flags))
                                wake_up(&conf->wait_for_overlap);
                        spin_unlock_irq(&conf->device_lock);
                        while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
                                copy_data(0, rbi, dev->page, dev->sector);
                                rbi2 = r5_next_bio(rbi, dev->sector);
                                spin_lock_irq(&conf->device_lock);
                                if (!raid5_dec_bi_phys_segments(rbi)) {
                                        rbi->bi_next = return_bi;
                                        return_bi = rbi;
                                }
                                spin_unlock_irq(&conf->device_lock);
                                rbi = rbi2;
                        }
                }

                /* now count some things */
                if (test_bit(R5_LOCKED, &dev->flags)) s.locked++;
                if (test_bit(R5_UPTODATE, &dev->flags)) s.uptodate++;


                if (dev->toread)
                        s.to_read++;
                if (dev->towrite) {
                        s.to_write++;
                        if (!test_bit(R5_OVERWRITE, &dev->flags))
                                s.non_overwrite++;
                }
                if (dev->written)
                        s.written++;
                rdev = rcu_dereference(conf->disks[i].rdev);
                if (blocked_rdev == NULL &&
                    rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
                        blocked_rdev = rdev;
                        atomic_inc(&rdev->nr_pending);
                }
                if (!rdev || !test_bit(In_sync, &rdev->flags)) {
                        /* The ReadError flag will just be confusing now */
                        clear_bit(R5_ReadError, &dev->flags);
                        clear_bit(R5_ReWrite, &dev->flags);
                }
                if (!rdev || !test_bit(In_sync, &rdev->flags)
                    || test_bit(R5_ReadError, &dev->flags)) {
                        if (s.failed < 2)
                                r6s.failed_num[s.failed] = i;
                        s.failed++;
                } else
                        set_bit(R5_Insync, &dev->flags);
        }
        rcu_read_unlock();

        if (unlikely(blocked_rdev)) {
                if (s.syncing || s.expanding || s.expanded ||
                    s.to_write || s.written) {
                        set_bit(STRIPE_HANDLE, &sh->state);
                        goto unlock;
                }
                /* There is nothing for the blocked_rdev to block */
                rdev_dec_pending(blocked_rdev, conf->mddev);
                blocked_rdev = NULL;
        }

        pr_debug("locked=%d uptodate=%d to_read=%d"
               " to_write=%d failed=%d failed_num=%d,%d\n",
               s.locked, s.uptodate, s.to_read, s.to_write, s.failed,
               r6s.failed_num[0], r6s.failed_num[1]);
        /* check if the array has lost >2 devices and, if so, some requests
         * might need to be failed
         */
        if (s.failed > 2 && s.to_read+s.to_write+s.written)
                handle_failed_stripe(conf, sh, &s, disks, &return_bi);
        if (s.failed > 2 && s.syncing) {
                md_done_sync(conf->mddev, STRIPE_SECTORS,0);
                clear_bit(STRIPE_SYNCING, &sh->state);
                s.syncing = 0;
        }

        /*
         * might be able to return some write requests if the parity blocks
         * are safe, or on a failed drive
         */
        pdev = &sh->dev[pd_idx];
        r6s.p_failed = (s.failed >= 1 && r6s.failed_num[0] == pd_idx)
                || (s.failed >= 2 && r6s.failed_num[1] == pd_idx);
        qdev = &sh->dev[qd_idx];
        r6s.q_failed = (s.failed >= 1 && r6s.failed_num[0] == qd_idx)
                || (s.failed >= 2 && r6s.failed_num[1] == qd_idx);

        if ( s.written &&
             ( r6s.p_failed || ((test_bit(R5_Insync, &pdev->flags)
                             && !test_bit(R5_LOCKED, &pdev->flags)
                             && test_bit(R5_UPTODATE, &pdev->flags)))) &&
             ( r6s.q_failed || ((test_bit(R5_Insync, &qdev->flags)
                             && !test_bit(R5_LOCKED, &qdev->flags)
                             && test_bit(R5_UPTODATE, &qdev->flags)))))
                handle_stripe_clean_event(conf, sh, disks, &return_bi);

        /* Now we might consider reading some blocks, either to check/generate
         * parity, or to satisfy requests
         * or to load a block that is being partially written.
         */
        if (s.to_read || s.non_overwrite || (s.to_write && s.failed) ||
            (s.syncing && (s.uptodate < disks)) || s.expanding)
                handle_stripe_fill6(sh, &s, &r6s, disks);

        /* now to consider writing and what else, if anything should be read */
        if (s.to_write)
                handle_stripe_dirtying6(conf, sh, &s, &r6s, disks);

        /* maybe we need to check and possibly fix the parity for this stripe
         * Any reads will already have been scheduled, so we just see if enough
         * data is available
         */
        if (s.syncing && s.locked == 0 && !test_bit(STRIPE_INSYNC, &sh->state))
                handle_parity_checks6(conf, sh, &s, &r6s, tmp_page, disks);

        if (s.syncing && s.locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
                md_done_sync(conf->mddev, STRIPE_SECTORS,1);
                clear_bit(STRIPE_SYNCING, &sh->state);
        }

        /* If the failed drives are just a ReadError, then we might need
         * to progress the repair/check process
         */
        if (s.failed <= 2 && !conf->mddev->ro)
                for (i = 0; i < s.failed; i++) {
                        dev = &sh->dev[r6s.failed_num[i]];
                        if (test_bit(R5_ReadError, &dev->flags)
                            && !test_bit(R5_LOCKED, &dev->flags)
                            && test_bit(R5_UPTODATE, &dev->flags)
                                ) {
                                if (!test_bit(R5_ReWrite, &dev->flags)) {
                                        set_bit(R5_Wantwrite, &dev->flags);
                                        set_bit(R5_ReWrite, &dev->flags);
                                        set_bit(R5_LOCKED, &dev->flags);
                                } else {
                                        /* let's read it back */
                                        set_bit(R5_Wantread, &dev->flags);
                                        set_bit(R5_LOCKED, &dev->flags);
                                }
                        }
                }

        if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state)) {
                struct stripe_head *sh2
                        = get_active_stripe(conf, sh->sector, 1, 1);
                if (sh2 && test_bit(STRIPE_EXPAND_SOURCE, &sh2->state)) {
                        /* sh cannot be written until sh2 has been read.
                         * so arrange for sh to be delayed a little
                         */
                        set_bit(STRIPE_DELAYED, &sh->state);
                        set_bit(STRIPE_HANDLE, &sh->state);
                        if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE,
                                              &sh2->state))
                                atomic_inc(&conf->preread_active_stripes);
                        release_stripe(sh2);
                        goto unlock;
                }
                if (sh2)
                        release_stripe(sh2);

                /* Need to write out all blocks after computing P&Q */
                sh->disks = conf->raid_disks;
                stripe_set_idx(sh->sector, conf, 0, sh);
                compute_parity6(sh, RECONSTRUCT_WRITE);
                for (i = conf->raid_disks ; i-- ;  ) {
                        set_bit(R5_LOCKED, &sh->dev[i].flags);
                        s.locked++;
                        set_bit(R5_Wantwrite, &sh->dev[i].flags);
                }
                clear_bit(STRIPE_EXPANDING, &sh->state);
        } else if (s.expanded) {
                clear_bit(STRIPE_EXPAND_READY, &sh->state);
                atomic_dec(&conf->reshape_stripes);
                wake_up(&conf->wait_for_overlap);
                md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
        }

        if (s.expanding && s.locked == 0 &&
            !test_bit(STRIPE_COMPUTE_RUN, &sh->state))
                handle_stripe_expansion(conf, sh, &r6s);

 unlock:
        spin_unlock(&sh->lock);

        /* wait for this device to become unblocked */
        if (unlikely(blocked_rdev))
                md_wait_for_blocked_rdev(blocked_rdev, conf->mddev);

        ops_run_io(sh, &s);

        return_io(return_bi);

        return blocked_rdev == NULL;
}

/* returns true if the stripe was handled */
static bool handle_stripe(struct stripe_head *sh, struct page *tmp_page)
{
        if (sh->raid_conf->level == 6)
                return handle_stripe6(sh, tmp_page);
        else
                return handle_stripe5(sh);
}



static void raid5_activate_delayed(raid5_conf_t *conf)
{
        if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD) {
                while (!list_empty(&conf->delayed_list)) {
                        struct list_head *l = conf->delayed_list.next;
                        struct stripe_head *sh;
                        sh = list_entry(l, struct stripe_head, lru);
                        list_del_init(l);
                        clear_bit(STRIPE_DELAYED, &sh->state);
                        if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                                atomic_inc(&conf->preread_active_stripes);
                        list_add_tail(&sh->lru, &conf->hold_list);
                }
        } else
                blk_plug_device(conf->mddev->queue);
}

static void activate_bit_delay(raid5_conf_t *conf)
{
        /* device_lock is held */
        struct list_head head;
        list_add(&head, &conf->bitmap_list);
        list_del_init(&conf->bitmap_list);
        while (!list_empty(&head)) {
                struct stripe_head *sh = list_entry(head.next, struct stripe_head, lru);
                list_del_init(&sh->lru);
                atomic_inc(&sh->count);
                __release_stripe(conf, sh);
        }
}

static void unplug_slaves(mddev_t *mddev)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);
        int i;

        rcu_read_lock();
        for (i=0; i<mddev->raid_disks; i++) {
                mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev);
                if (rdev && !test_bit(Faulty, &rdev->flags) && atomic_read(&rdev->nr_pending)) {
                        struct request_queue *r_queue = bdev_get_queue(rdev->bdev);

                        atomic_inc(&rdev->nr_pending);
                        rcu_read_unlock();

                        blk_unplug(r_queue);

                        rdev_dec_pending(rdev, mddev);
                        rcu_read_lock();
                }
        }
        rcu_read_unlock();
}

static void raid5_unplug_device(struct request_queue *q)
{
        mddev_t *mddev = q->queuedata;
        raid5_conf_t *conf = mddev_to_conf(mddev);
        unsigned long flags;

        spin_lock_irqsave(&conf->device_lock, flags);

        if (blk_remove_plug(q)) {
                conf->seq_flush++;
                raid5_activate_delayed(conf);
        }
        md_wakeup_thread(mddev->thread);

        spin_unlock_irqrestore(&conf->device_lock, flags);

        unplug_slaves(mddev);
}

static int raid5_congested(void *data, int bits)
{
        mddev_t *mddev = data;
        raid5_conf_t *conf = mddev_to_conf(mddev);

        /* No difference between reads and writes.  Just check
         * how busy the stripe_cache is
         */
        if (conf->inactive_blocked)
                return 1;
        if (conf->quiesce)
                return 1;
        if (list_empty_careful(&conf->inactive_list))
                return 1;

        return 0;
}

/* We want read requests to align with chunks where possible,
 * but write requests don't need to.
 */
static int raid5_mergeable_bvec(struct request_queue *q,
                                struct bvec_merge_data *bvm,
                                struct bio_vec *biovec)
{
        mddev_t *mddev = q->queuedata;
        sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
        int max;
        unsigned int chunk_sectors = mddev->chunk_size >> 9;
        unsigned int bio_sectors = bvm->bi_size >> 9;

        if ((bvm->bi_rw & 1) == WRITE)
                return biovec->bv_len; /* always allow writes to be mergeable */

        if (mddev->new_chunk < mddev->chunk_size)
                chunk_sectors = mddev->new_chunk >> 9;
        max =  (chunk_sectors - ((sector & (chunk_sectors - 1)) + bio_sectors)) << 9;
        if (max < 0) max = 0;
        if (max <= biovec->bv_len && bio_sectors == 0)
                return biovec->bv_len;
        else
                return max;
}


static int in_chunk_boundary(mddev_t *mddev, struct bio *bio)
{
        sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);
        unsigned int chunk_sectors = mddev->chunk_size >> 9;
        unsigned int bio_sectors = bio->bi_size >> 9;

        if (mddev->new_chunk < mddev->chunk_size)
                chunk_sectors = mddev->new_chunk >> 9;
        return  chunk_sectors >=
                ((sector & (chunk_sectors - 1)) + bio_sectors);
}

/*
 *  add bio to the retry LIFO  ( in O(1) ... we are in interrupt )
 *  later sampled by raid5d.
 */
static void add_bio_to_retry(struct bio *bi,raid5_conf_t *conf)
{
        unsigned long flags;

        spin_lock_irqsave(&conf->device_lock, flags);

        bi->bi_next = conf->retry_read_aligned_list;
        conf->retry_read_aligned_list = bi;

        spin_unlock_irqrestore(&conf->device_lock, flags);
        md_wakeup_thread(conf->mddev->thread);
}


static struct bio *remove_bio_from_retry(raid5_conf_t *conf)
{
        struct bio *bi;

        bi = conf->retry_read_aligned;
        if (bi) {
                conf->retry_read_aligned = NULL;
                return bi;
        }
        bi = conf->retry_read_aligned_list;
        if(bi) {
                conf->retry_read_aligned_list = bi->bi_next;
                bi->bi_next = NULL;
                /*
                 * this sets the active strip count to 1 and the processed
                 * strip count to zero (upper 8 bits)
                 */
                bi->bi_phys_segments = 1; /* biased count of active stripes */
        }

        return bi;
}


/*
 *  The "raid5_align_endio" should check if the read succeeded and if it
 *  did, call bio_endio on the original bio (having bio_put the new bio
 *  first).
 *  If the read failed..
 */
static void raid5_align_endio(struct bio *bi, int error)
{
        struct bio* raid_bi  = bi->bi_private;
        mddev_t *mddev;
        raid5_conf_t *conf;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
        mdk_rdev_t *rdev;

        bio_put(bi);

        mddev = raid_bi->bi_bdev->bd_disk->queue->queuedata;
        conf = mddev_to_conf(mddev);
        rdev = (void*)raid_bi->bi_next;
        raid_bi->bi_next = NULL;

        rdev_dec_pending(rdev, conf->mddev);

        if (!error && uptodate) {
                bio_endio(raid_bi, 0);
                if (atomic_dec_and_test(&conf->active_aligned_reads))
                        wake_up(&conf->wait_for_stripe);
                return;
        }


        pr_debug("raid5_align_endio : io error...handing IO for a retry\n");

        add_bio_to_retry(raid_bi, conf);
}

static int bio_fits_rdev(struct bio *bi)
{
        struct request_queue *q = bdev_get_queue(bi->bi_bdev);

        if ((bi->bi_size>>9) > q->max_sectors)
                return 0;
        blk_recount_segments(q, bi);
        if (bi->bi_phys_segments > q->max_phys_segments)
                return 0;

        if (q->merge_bvec_fn)
                /* it's too hard to apply the merge_bvec_fn at this stage,
                 * just just give up
                 */
                return 0;

        return 1;
}


static int chunk_aligned_read(struct request_queue *q, struct bio * raid_bio)
{
        mddev_t *mddev = q->queuedata;
        raid5_conf_t *conf = mddev_to_conf(mddev);
        unsigned int dd_idx;
        struct bio* align_bi;
        mdk_rdev_t *rdev;

        if (!in_chunk_boundary(mddev, raid_bio)) {
                pr_debug("chunk_aligned_read : non aligned\n");
                return 0;
        }
        /*
         * use bio_clone to make a copy of the bio
         */
        align_bi = bio_clone(raid_bio, GFP_NOIO);
        if (!align_bi)
                return 0;
        /*
         *   set bi_end_io to a new function, and set bi_private to the
         *     original bio.
         */
        align_bi->bi_end_io  = raid5_align_endio;
        align_bi->bi_private = raid_bio;
        /*
         *      compute position
         */
        align_bi->bi_sector =  raid5_compute_sector(conf, raid_bio->bi_sector,
                                                    0,
                                                    &dd_idx, NULL);

        rcu_read_lock();
        rdev = rcu_dereference(conf->disks[dd_idx].rdev);
        if (rdev && test_bit(In_sync, &rdev->flags)) {
                atomic_inc(&rdev->nr_pending);
                rcu_read_unlock();
                raid_bio->bi_next = (void*)rdev;
                align_bi->bi_bdev =  rdev->bdev;
                align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
                align_bi->bi_sector += rdev->data_offset;

                if (!bio_fits_rdev(align_bi)) {
                        /* too big in some way */
                        bio_put(align_bi);
                        rdev_dec_pending(rdev, mddev);
                        return 0;
                }

                spin_lock_irq(&conf->device_lock);
                wait_event_lock_irq(conf->wait_for_stripe,
                                    conf->quiesce == 0,
                                    conf->device_lock, /* nothing */);
                atomic_inc(&conf->active_aligned_reads);
                spin_unlock_irq(&conf->device_lock);

                generic_make_request(align_bi);
                return 1;
        } else {
                rcu_read_unlock();
                bio_put(align_bi);
                return 0;
        }
}

/* __get_priority_stripe - get the next stripe to process
 *
 * Full stripe writes are allowed to pass preread active stripes up until
 * the bypass_threshold is exceeded.  In general the bypass_count
 * increments when the handle_list is handled before the hold_list; however, it
 * will not be incremented when STRIPE_IO_STARTED is sampled set signifying a
 * stripe with in flight i/o.  The bypass_count will be reset when the
 * head of the hold_list has changed, i.e. the head was promoted to the
 * handle_list.
 */
static struct stripe_head *__get_priority_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh;

        pr_debug("%s: handle: %s hold: %s full_writes: %d bypass_count: %d\n",
                  __func__,
                  list_empty(&conf->handle_list) ? "empty" : "busy",
                  list_empty(&conf->hold_list) ? "empty" : "busy",
                  atomic_read(&conf->pending_full_writes), conf->bypass_count);

        if (!list_empty(&conf->handle_list)) {
                sh = list_entry(conf->handle_list.next, typeof(*sh), lru);

                if (list_empty(&conf->hold_list))
                        conf->bypass_count = 0;
                else if (!test_bit(STRIPE_IO_STARTED, &sh->state)) {
                        if (conf->hold_list.next == conf->last_hold)
                                conf->bypass_count++;
                        else {
                                conf->last_hold = conf->hold_list.next;
                                conf->bypass_count -= conf->bypass_threshold;
                                if (conf->bypass_count < 0)
                                        conf->bypass_count = 0;
                        }
                }
        } else if (!list_empty(&conf->hold_list) &&
                   ((conf->bypass_threshold &&
                     conf->bypass_count > conf->bypass_threshold) ||
                    atomic_read(&conf->pending_full_writes) == 0)) {
                sh = list_entry(conf->hold_list.next,
                                typeof(*sh), lru);
                conf->bypass_count -= conf->bypass_threshold;
                if (conf->bypass_count < 0)
                        conf->bypass_count = 0;
        } else
                return NULL;

        list_del_init(&sh->lru);
        atomic_inc(&sh->count);
        BUG_ON(atomic_read(&sh->count) != 1);
        return sh;
}

static int make_request(struct request_queue *q, struct bio * bi)
{
        mddev_t *mddev = q->queuedata;
        raid5_conf_t *conf = mddev_to_conf(mddev);
        int dd_idx;
        sector_t new_sector;
        sector_t logical_sector, last_sector;
        struct stripe_head *sh;
        const int rw = bio_data_dir(bi);
        int cpu, remaining;

        if (unlikely(bio_barrier(bi))) {
                bio_endio(bi, -EOPNOTSUPP);
                return 0;
        }

        md_write_start(mddev, bi);

        cpu = part_stat_lock();
        part_stat_inc(cpu, &mddev->gendisk->part0, ios[rw]);
        part_stat_add(cpu, &mddev->gendisk->part0, sectors[rw],
                      bio_sectors(bi));
        part_stat_unlock();

        if (rw == READ &&
             mddev->reshape_position == MaxSector &&
             chunk_aligned_read(q,bi))
                return 0;

        logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
        last_sector = bi->bi_sector + (bi->bi_size>>9);
        bi->bi_next = NULL;
        bi->bi_phys_segments = 1;       /* over-loaded to count active stripes */

        for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
                DEFINE_WAIT(w);
                int disks, data_disks;
                int previous;

        retry:
                previous = 0;
                prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
                if (likely(conf->reshape_progress == MaxSector))
                        disks = conf->raid_disks;
                else {
                        /* spinlock is needed as reshape_progress may be
                         * 64bit on a 32bit platform, and so it might be
                         * possible to see a half-updated value
                         * Ofcourse reshape_progress could change after
                         * the lock is dropped, so once we get a reference
                         * to the stripe that we think it is, we will have
                         * to check again.
                         */
                        spin_lock_irq(&conf->device_lock);
                        disks = conf->raid_disks;
                        if (mddev->delta_disks < 0
                            ? logical_sector < conf->reshape_progress
                            : logical_sector >= conf->reshape_progress) {
                                disks = conf->previous_raid_disks;
                                previous = 1;
                        } else {
                                if (mddev->delta_disks < 0
                                    ? logical_sector < conf->reshape_safe
                                    : logical_sector >= conf->reshape_safe) {
                                        spin_unlock_irq(&conf->device_lock);
                                        schedule();
                                        goto retry;
                                }
                        }
                        spin_unlock_irq(&conf->device_lock);
                }
                data_disks = disks - conf->max_degraded;

                new_sector = raid5_compute_sector(conf, logical_sector,
                                                  previous,
                                                  &dd_idx, NULL);
                pr_debug("raid5: make_request, sector %llu logical %llu\n",
                        (unsigned long long)new_sector, 
                        (unsigned long long)logical_sector);

                sh = get_active_stripe(conf, new_sector, previous,
                                       (bi->bi_rw&RWA_MASK));
                if (sh) {
                        if (unlikely(conf->reshape_progress != MaxSector)) {
                                /* expansion might have moved on while waiting for a
                                 * stripe, so we must do the range check again.
                                 * Expansion could still move past after this
                                 * test, but as we are holding a reference to
                                 * 'sh', we know that if that happens,
                                 *  STRIPE_EXPANDING will get set and the expansion
                                 * won't proceed until we finish with the stripe.
                                 */
                                int must_retry = 0;
                                spin_lock_irq(&conf->device_lock);
                                if ((mddev->delta_disks < 0
                                     ? logical_sector >= conf->reshape_progress
                                     : logical_sector < conf->reshape_progress)
                                    && previous)
                                        /* mismatch, need to try again */
                                        must_retry = 1;
                                spin_unlock_irq(&conf->device_lock);
                                if (must_retry) {
                                        release_stripe(sh);
                                        goto retry;
                                }
                        }
                        /* FIXME what if we get a false positive because these
                         * are being updated.
                         */
                        if (logical_sector >= mddev->suspend_lo &&
                            logical_sector < mddev->suspend_hi) {
                                release_stripe(sh);
                                schedule();
                                goto retry;
                        }

                        if (test_bit(STRIPE_EXPANDING, &sh->state) ||
                            !add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
                                /* Stripe is busy expanding or
                                 * add failed due to overlap.  Flush everything
                                 * and wait a while
                                 */
                                raid5_unplug_device(mddev->queue);
                                release_stripe(sh);
                                schedule();
                                goto retry;
                        }
                        finish_wait(&conf->wait_for_overlap, &w);
                        set_bit(STRIPE_HANDLE, &sh->state);
                        clear_bit(STRIPE_DELAYED, &sh->state);
                        release_stripe(sh);
                } else {
                        /* cannot get stripe for read-ahead, just give-up */
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
                        finish_wait(&conf->wait_for_overlap, &w);
                        break;
                }
                        
        }
        spin_lock_irq(&conf->device_lock);
        remaining = raid5_dec_bi_phys_segments(bi);
        spin_unlock_irq(&conf->device_lock);
        if (remaining == 0) {

                if ( rw == WRITE )
                        md_write_end(mddev);

                bio_endio(bi, 0);
        }
        return 0;
}

static sector_t raid5_size(mddev_t *mddev, sector_t sectors, int raid_disks);

static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped)
{
        /* reshaping is quite different to recovery/resync so it is
         * handled quite separately ... here.
         *
         * On each call to sync_request, we gather one chunk worth of
         * destination stripes and flag them as expanding.
         * Then we find all the source stripes and request reads.
         * As the reads complete, handle_stripe will copy the data
         * into the destination stripe and release that stripe.
         */
        raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
        struct stripe_head *sh;
        sector_t first_sector, last_sector;
        int raid_disks = conf->previous_raid_disks;
        int data_disks = raid_disks - conf->max_degraded;
        int new_data_disks = conf->raid_disks - conf->max_degraded;
        int i;
        int dd_idx;
        sector_t writepos, safepos, gap;
        sector_t stripe_addr;
        int reshape_sectors;
        struct list_head stripes;

        if (sector_nr == 0) {
                /* If restarting in the middle, skip the initial sectors */
                if (mddev->delta_disks < 0 &&
                    conf->reshape_progress < raid5_size(mddev, 0, 0)) {
                        sector_nr = raid5_size(mddev, 0, 0)
                                - conf->reshape_progress;
                } else if (mddev->delta_disks > 0 &&
                           conf->reshape_progress > 0)
                        sector_nr = conf->reshape_progress;
                sector_div(sector_nr, new_data_disks);
                if (sector_nr) {
                        *skipped = 1;
                        return sector_nr;
                }
        }

        /* We need to process a full chunk at a time.
         * If old and new chunk sizes differ, we need to process the
         * largest of these
         */
        if (mddev->new_chunk > mddev->chunk_size)
                reshape_sectors = mddev->new_chunk / 512;
        else
                reshape_sectors = mddev->chunk_size / 512;

        /* we update the metadata when there is more than 3Meg
         * in the block range (that is rather arbitrary, should
         * probably be time based) or when the data about to be
         * copied would over-write the source of the data at
         * the front of the range.
         * i.e. one new_stripe along from reshape_progress new_maps
         * to after where reshape_safe old_maps to
         */
        writepos = conf->reshape_progress;
        sector_div(writepos, new_data_disks);
        safepos = conf->reshape_safe;
        sector_div(safepos, data_disks);
        if (mddev->delta_disks < 0) {
                writepos -= reshape_sectors;
                safepos += reshape_sectors;
                gap = conf->reshape_safe - conf->reshape_progress;
        } else {
                writepos += reshape_sectors;
                safepos -= reshape_sectors;
                gap = conf->reshape_progress - conf->reshape_safe;
        }

        if ((mddev->delta_disks < 0
             ? writepos < safepos
             : writepos > safepos) ||
            gap > (new_data_disks)*3000*2 /*3Meg*/) {
                /* Cannot proceed until we've updated the superblock... */
                wait_event(conf->wait_for_overlap,
                           atomic_read(&conf->reshape_stripes)==0);
                mddev->reshape_position = conf->reshape_progress;
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait, mddev->flags == 0 ||
                           kthread_should_stop());
                spin_lock_irq(&conf->device_lock);
                conf->reshape_safe = mddev->reshape_position;
                spin_unlock_irq(&conf->device_lock);
                wake_up(&conf->wait_for_overlap);
        }

        if (mddev->delta_disks < 0) {
                BUG_ON(conf->reshape_progress == 0);
                stripe_addr = writepos;
                BUG_ON((mddev->dev_sectors &
                        ~((sector_t)reshape_sectors - 1))
                       - reshape_sectors - stripe_addr
                       != sector_nr);
        } else {
                BUG_ON(writepos != sector_nr + reshape_sectors);
                stripe_addr = sector_nr;
        }
        INIT_LIST_HEAD(&stripes);
        for (i = 0; i < reshape_sectors; i += STRIPE_SECTORS) {
                int j;
                int skipped = 0;
                sh = get_active_stripe(conf, stripe_addr+i, 0, 0);
                set_bit(STRIPE_EXPANDING, &sh->state);
                atomic_inc(&conf->reshape_stripes);
                /* If any of this stripe is beyond the end of the old
                 * array, then we need to zero those blocks
                 */
                for (j=sh->disks; j--;) {
                        sector_t s;
                        if (j == sh->pd_idx)
                                continue;
                        if (conf->level == 6 &&
                            j == sh->qd_idx)
                                continue;
                        s = compute_blocknr(sh, j, 0);
                        if (s < raid5_size(mddev, 0, 0)) {
                                skipped = 1;
                                continue;
                        }
                        memset(page_address(sh->dev[j].page), 0, STRIPE_SIZE);
                        set_bit(R5_Expanded, &sh->dev[j].flags);
                        set_bit(R5_UPTODATE, &sh->dev[j].flags);
                }
                if (!skipped) {
                        set_bit(STRIPE_EXPAND_READY, &sh->state);
                        set_bit(STRIPE_HANDLE, &sh->state);
                }
                list_add(&sh->lru, &stripes);
        }
        spin_lock_irq(&conf->device_lock);
        if (mddev->delta_disks < 0)
                conf->reshape_progress -= reshape_sectors * new_data_disks;
        else
                conf->reshape_progress += reshape_sectors * new_data_disks;
        spin_unlock_irq(&conf->device_lock);
        /* Ok, those stripe are ready. We can start scheduling
         * reads on the source stripes.
         * The source stripes are determined by mapping the first and last
         * block on the destination stripes.
         */
        first_sector =
                raid5_compute_sector(conf, stripe_addr*(new_data_disks),
                                     1, &dd_idx, NULL);
        last_sector =
                raid5_compute_sector(conf, ((stripe_addr+conf->chunk_size/512)
                                            *(new_data_disks) - 1),
                                     1, &dd_idx, NULL);
        if (last_sector >= mddev->dev_sectors)
                last_sector = mddev->dev_sectors - 1;
        while (first_sector <= last_sector) {
                sh = get_active_stripe(conf, first_sector, 1, 0);
                set_bit(STRIPE_EXPAND_SOURCE, &sh->state);
                set_bit(STRIPE_HANDLE, &sh->state);
                release_stripe(sh);
                first_sector += STRIPE_SECTORS;
        }
        /* Now that the sources are clearly marked, we can release
         * the destination stripes
         */
        while (!list_empty(&stripes)) {
                sh = list_entry(stripes.next, struct stripe_head, lru);
                list_del_init(&sh->lru);
                release_stripe(sh);
        }
        /* If this takes us to the resync_max point where we have to pause,
         * then we need to write out the superblock.
         */
        sector_nr += reshape_sectors;
        if (sector_nr >= mddev->resync_max) {
                /* Cannot proceed until we've updated the superblock... */
                wait_event(conf->wait_for_overlap,
                           atomic_read(&conf->reshape_stripes) == 0);
                mddev->reshape_position = conf->reshape_progress;
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait,
                           !test_bit(MD_CHANGE_DEVS, &mddev->flags)
                           || kthread_should_stop());
                spin_lock_irq(&conf->device_lock);
                conf->reshape_safe = mddev->reshape_position;
                spin_unlock_irq(&conf->device_lock);
                wake_up(&conf->wait_for_overlap);
        }
        return reshape_sectors;
}

/* FIXME go_faster isn't used */
static inline sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, int go_faster)
{
        raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
        struct stripe_head *sh;
        sector_t max_sector = mddev->dev_sectors;
        int sync_blocks;
        int still_degraded = 0;
        int i;

        if (sector_nr >= max_sector) {
                /* just being told to finish up .. nothing much to do */
                unplug_slaves(mddev);

                if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery)) {
                        end_reshape(conf);
                        return 0;
                }

                if (mddev->curr_resync < max_sector) /* aborted */
                        bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
                                        &sync_blocks, 1);
                else /* completed sync */
                        conf->fullsync = 0;
                bitmap_close_sync(mddev->bitmap);

                return 0;
        }

        if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
                return reshape_request(mddev, sector_nr, skipped);

        /* No need to check resync_max as we never do more than one
         * stripe, and as resync_max will always be on a chunk boundary,
         * if the check in md_do_sync didn't fire, there is no chance
         * of overstepping resync_max here
         */

        /* if there is too many failed drives and we are trying
         * to resync, then assert that we are finished, because there is
         * nothing we can do.
         */
        if (mddev->degraded >= conf->max_degraded &&
            test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
                sector_t rv = mddev->dev_sectors - sector_nr;
                *skipped = 1;
                return rv;
        }
        if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
            !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
            !conf->fullsync && sync_blocks >= STRIPE_SECTORS) {
                /* we can skip this block, and probably more */
                sync_blocks /= STRIPE_SECTORS;
                *skipped = 1;
                return sync_blocks * STRIPE_SECTORS; /* keep things rounded to whole stripes */
        }


        bitmap_cond_end_sync(mddev->bitmap, sector_nr);

        sh = get_active_stripe(conf, sector_nr, 0, 1);
        if (sh == NULL) {
                sh = get_active_stripe(conf, sector_nr, 0, 0);
                /* make sure we don't swamp the stripe cache if someone else
                 * is trying to get access
                 */
                schedule_timeout_uninterruptible(1);
        }
        /* Need to check if array will still be degraded after recovery/resync
         * We don't need to check the 'failed' flag as when that gets set,
         * recovery aborts.
         */
        for (i=0; i<mddev->raid_disks; i++)
                if (conf->disks[i].rdev == NULL)
                        still_degraded = 1;

        bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, still_degraded);

        spin_lock(&sh->lock);
        set_bit(STRIPE_SYNCING, &sh->state);
        clear_bit(STRIPE_INSYNC, &sh->state);
        spin_unlock(&sh->lock);

        /* wait for any blocked device to be handled */
        while(unlikely(!handle_stripe(sh, NULL)))
                ;
        release_stripe(sh);

        return STRIPE_SECTORS;
}

static int  retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
{
        /* We may not be able to submit a whole bio at once as there
         * may not be enough stripe_heads available.
         * We cannot pre-allocate enough stripe_heads as we may need
         * more than exist in the cache (if we allow ever large chunks).
         * So we do one stripe head at a time and record in
         * ->bi_hw_segments how many have been done.
         *
         * We *know* that this entire raid_bio is in one chunk, so
         * it will be only one 'dd_idx' and only need one call to raid5_compute_sector.
         */
        struct stripe_head *sh;
        int dd_idx;
        sector_t sector, logical_sector, last_sector;
        int scnt = 0;
        int remaining;
        int handled = 0;

        logical_sector = raid_bio->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
        sector = raid5_compute_sector(conf, logical_sector,
                                      0, &dd_idx, NULL);
        last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);

        for (; logical_sector < last_sector;
             logical_sector += STRIPE_SECTORS,
                     sector += STRIPE_SECTORS,
                     scnt++) {

                if (scnt < raid5_bi_hw_segments(raid_bio))
                        /* already done this stripe */
                        continue;

                sh = get_active_stripe(conf, sector, 0, 1);

                if (!sh) {
                        /* failed to get a stripe - must wait */
                        raid5_set_bi_hw_segments(raid_bio, scnt);
                        conf->retry_read_aligned = raid_bio;
                        return handled;
                }

                set_bit(R5_ReadError, &sh->dev[dd_idx].flags);
                if (!add_stripe_bio(sh, raid_bio, dd_idx, 0)) {
                        release_stripe(sh);
                        raid5_set_bi_hw_segments(raid_bio, scnt);
                        conf->retry_read_aligned = raid_bio;
                        return handled;
                }

                handle_stripe(sh, NULL);
                release_stripe(sh);
                handled++;
        }
        spin_lock_irq(&conf->device_lock);
        remaining = raid5_dec_bi_phys_segments(raid_bio);
        spin_unlock_irq(&conf->device_lock);
        if (remaining == 0)
                bio_endio(raid_bio, 0);
        if (atomic_dec_and_test(&conf->active_aligned_reads))
                wake_up(&conf->wait_for_stripe);
        return handled;
}



/*
 * This is our raid5 kernel thread.
 *
 * We scan the hash table for stripes which can be handled now.
 * During the scan, completed stripes are saved for us by the interrupt
 * handler, so that they will not have to wait for our next wakeup.
 */
static void raid5d(mddev_t *mddev)
{
        struct stripe_head *sh;
        raid5_conf_t *conf = mddev_to_conf(mddev);
        int handled;

        pr_debug("+++ raid5d active\n");

        md_check_recovery(mddev);

        handled = 0;
        spin_lock_irq(&conf->device_lock);
        while (1) {
                struct bio *bio;

                if (conf->seq_flush != conf->seq_write) {
                        int seq = conf->seq_flush;
                        spin_unlock_irq(&conf->device_lock);
                        bitmap_unplug(mddev->bitmap);
                        spin_lock_irq(&conf->device_lock);
                        conf->seq_write = seq;
                        activate_bit_delay(conf);
                }

                while ((bio = remove_bio_from_retry(conf))) {
                        int ok;
                        spin_unlock_irq(&conf->device_lock);
                        ok = retry_aligned_read(conf, bio);
                        spin_lock_irq(&conf->device_lock);
                        if (!ok)
                                break;
                        handled++;
                }

                sh = __get_priority_stripe(conf);

                if (!sh)
                        break;
                spin_unlock_irq(&conf->device_lock);
                
                handled++;
                handle_stripe(sh, conf->spare_page);
                release_stripe(sh);

                spin_lock_irq(&conf->device_lock);
        }
        pr_debug("%d stripes handled\n", handled);

        spin_unlock_irq(&conf->device_lock);

        async_tx_issue_pending_all();
        unplug_slaves(mddev);

        pr_debug("--- raid5d inactive\n");
}

static ssize_t
raid5_show_stripe_cache_size(mddev_t *mddev, char *page)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);
        if (conf)
                return sprintf(page, "%d\n", conf->max_nr_stripes);
        else
                return 0;
}

static ssize_t
raid5_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);
        unsigned long new;
        int err;

        if (len >= PAGE_SIZE)
                return -EINVAL;
        if (!conf)
                return -ENODEV;

        if (strict_strtoul(page, 10, &new))
                return -EINVAL;
        if (new <= 16 || new > 32768)
                return -EINVAL;
        while (new < conf->max_nr_stripes) {
                if (drop_one_stripe(conf))
                        conf->max_nr_stripes--;
                else
                        break;
        }
        err = md_allow_write(mddev);
        if (err)
                return err;
        while (new > conf->max_nr_stripes) {
                if (grow_one_stripe(conf))
                        conf->max_nr_stripes++;
                else break;
        }
        return len;
}

static struct md_sysfs_entry
raid5_stripecache_size = __ATTR(stripe_cache_size, S_IRUGO | S_IWUSR,
                                raid5_show_stripe_cache_size,
                                raid5_store_stripe_cache_size);

static ssize_t
raid5_show_preread_threshold(mddev_t *mddev, char *page)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);
        if (conf)
                return sprintf(page, "%d\n", conf->bypass_threshold);
        else
                return 0;
}

static ssize_t
raid5_store_preread_threshold(mddev_t *mddev, const char *page, size_t len)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);
        unsigned long new;
        if (len >= PAGE_SIZE)
                return -EINVAL;
        if (!conf)
                return -ENODEV;

        if (strict_strtoul(page, 10, &new))
                return -EINVAL;
        if (new > conf->max_nr_stripes)
                return -EINVAL;
        conf->bypass_threshold = new;
        return len;
}

static struct md_sysfs_entry
raid5_preread_bypass_threshold = __ATTR(preread_bypass_threshold,
                                        S_IRUGO | S_IWUSR,
                                        raid5_show_preread_threshold,
                                        raid5_store_preread_threshold);

static ssize_t
stripe_cache_active_show(mddev_t *mddev, char *page)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);
        if (conf)
                return sprintf(page, "%d\n", atomic_read(&conf->active_stripes));
        else
                return 0;
}

static struct md_sysfs_entry
raid5_stripecache_active = __ATTR_RO(stripe_cache_active);

static struct attribute *raid5_attrs[] =  {
        &raid5_stripecache_size.attr,
        &raid5_stripecache_active.attr,
        &raid5_preread_bypass_threshold.attr,
        NULL,
};
static struct attribute_group raid5_attrs_group = {
        .name = NULL,
        .attrs = raid5_attrs,
};

static sector_t
raid5_size(mddev_t *mddev, sector_t sectors, int raid_disks)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);

        if (!sectors)
                sectors = mddev->dev_sectors;
        if (!raid_disks) {
                /* size is defined by the smallest of previous and new size */
                if (conf->raid_disks < conf->previous_raid_disks)
                        raid_disks = conf->raid_disks;
                else
                        raid_disks = conf->previous_raid_disks;
        }

        sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
        sectors &= ~((sector_t)mddev->new_chunk/512 - 1);
        return sectors * (raid_disks - conf->max_degraded);
}

static raid5_conf_t *setup_conf(mddev_t *mddev)
{
        raid5_conf_t *conf;
        int raid_disk, memory;
        mdk_rdev_t *rdev;
        struct disk_info *disk;

        if (mddev->new_level != 5
            && mddev->new_level != 4
            && mddev->new_level != 6) {
                printk(KERN_ERR "raid5: %s: raid level not set to 4/5/6 (%d)\n",
                       mdname(mddev), mddev->new_level);
                return ERR_PTR(-EIO);
        }
        if ((mddev->new_level == 5
             && !algorithm_valid_raid5(mddev->new_layout)) ||
            (mddev->new_level == 6
             && !algorithm_valid_raid6(mddev->new_layout))) {
                printk(KERN_ERR "raid5: %s: layout %d not supported\n",
                       mdname(mddev), mddev->new_layout);
                return ERR_PTR(-EIO);
        }
        if (mddev->new_level == 6 && mddev->raid_disks < 4) {
                printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
                       mdname(mddev), mddev->raid_disks);
                return ERR_PTR(-EINVAL);
        }

        if (!mddev->new_chunk || mddev->new_chunk % PAGE_SIZE) {
                printk(KERN_ERR "raid5: invalid chunk size %d for %s\n",
                        mddev->new_chunk, mdname(mddev));
                return ERR_PTR(-EINVAL);
        }

        conf = kzalloc(sizeof(raid5_conf_t), GFP_KERNEL);
        if (conf == NULL)
                goto abort;

        conf->raid_disks = mddev->raid_disks;
        if (mddev->reshape_position == MaxSector)
                conf->previous_raid_disks = mddev->raid_disks;
        else
                conf->previous_raid_disks = mddev->raid_disks - mddev->delta_disks;

        conf->disks = kzalloc(conf->raid_disks * sizeof(struct disk_info),
                              GFP_KERNEL);
        if (!conf->disks)
                goto abort;

        conf->mddev = mddev;

        if ((conf->stripe_hashtbl = kzalloc(PAGE_SIZE, GFP_KERNEL)) == NULL)
                goto abort;

        if (mddev->new_level == 6) {
                conf->spare_page = alloc_page(GFP_KERNEL);
                if (!conf->spare_page)
                        goto abort;
        }
        spin_lock_init(&conf->device_lock);
        init_waitqueue_head(&conf->wait_for_stripe);
        init_waitqueue_head(&conf->wait_for_overlap);
        INIT_LIST_HEAD(&conf->handle_list);
        INIT_LIST_HEAD(&conf->hold_list);
        INIT_LIST_HEAD(&conf->delayed_list);
        INIT_LIST_HEAD(&conf->bitmap_list);
        INIT_LIST_HEAD(&conf->inactive_list);
        atomic_set(&conf->active_stripes, 0);
        atomic_set(&conf->preread_active_stripes, 0);
        atomic_set(&conf->active_aligned_reads, 0);
        conf->bypass_threshold = BYPASS_THRESHOLD;

        pr_debug("raid5: run(%s) called.\n", mdname(mddev));

        list_for_each_entry(rdev, &mddev->disks, same_set) {
                raid_disk = rdev->raid_disk;
                if (raid_disk >= conf->raid_disks
                    || raid_disk < 0)
                        continue;
                disk = conf->disks + raid_disk;

                disk->rdev = rdev;

                if (test_bit(In_sync, &rdev->flags)) {
                        char b[BDEVNAME_SIZE];
                        printk(KERN_INFO "raid5: device %s operational as raid"
                                " disk %d\n", bdevname(rdev->bdev,b),
                                raid_disk);
                } else
                        /* Cannot rely on bitmap to complete recovery */
                        conf->fullsync = 1;
        }

        conf->chunk_size = mddev->new_chunk;
        conf->level = mddev->new_level;
        if (conf->level == 6)
                conf->max_degraded = 2;
        else
                conf->max_degraded = 1;
        conf->algorithm = mddev->new_layout;
        conf->max_nr_stripes = NR_STRIPES;
        conf->reshape_progress = mddev->reshape_position;
        if (conf->reshape_progress != MaxSector) {
                conf->prev_chunk = mddev->chunk_size;
                conf->prev_algo = mddev->layout;
        }

        memory = conf->max_nr_stripes * (sizeof(struct stripe_head) +
                 conf->raid_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
        if (grow_stripes(conf, conf->max_nr_stripes)) {
                printk(KERN_ERR
                        "raid5: couldn't allocate %dkB for buffers\n", memory);
                goto abort;
        } else
                printk(KERN_INFO "raid5: allocated %dkB for %s\n",
                        memory, mdname(mddev));

        conf->thread = md_register_thread(raid5d, mddev, "%s_raid5");
        if (!conf->thread) {
                printk(KERN_ERR
                       "raid5: couldn't allocate thread for %s\n",
                       mdname(mddev));
                goto abort;
        }

        return conf;

 abort:
        if (conf) {
                shrink_stripes(conf);
                safe_put_page(conf->spare_page);
                kfree(conf->disks);
                kfree(conf->stripe_hashtbl);
                kfree(conf);
                return ERR_PTR(-EIO);
        } else
                return ERR_PTR(-ENOMEM);
}

static int run(mddev_t *mddev)
{
        raid5_conf_t *conf;
        int working_disks = 0;
        mdk_rdev_t *rdev;

        if (mddev->reshape_position != MaxSector) {
                /* Check that we can continue the reshape.
                 * Currently only disks can change, it must
                 * increase, and we must be past the point where
                 * a stripe over-writes itself
                 */
                sector_t here_new, here_old;
                int old_disks;
                int max_degraded = (mddev->level == 6 ? 2 : 1);

                if (mddev->new_level != mddev->level) {
                        printk(KERN_ERR "raid5: %s: unsupported reshape "
                               "required - aborting.\n",
                               mdname(mddev));
                        return -EINVAL;
                }
                old_disks = mddev->raid_disks - mddev->delta_disks;
                /* reshape_position must be on a new-stripe boundary, and one
                 * further up in new geometry must map after here in old
                 * geometry.
                 */
                here_new = mddev->reshape_position;
                if (sector_div(here_new, (mddev->new_chunk>>9)*
                               (mddev->raid_disks - max_degraded))) {
                        printk(KERN_ERR "raid5: reshape_position not "
                               "on a stripe boundary\n");
                        return -EINVAL;
                }
                /* here_new is the stripe we will write to */
                here_old = mddev->reshape_position;
                sector_div(here_old, (mddev->chunk_size>>9)*
                           (old_disks-max_degraded));
                /* here_old is the first stripe that we might need to read
                 * from */
                if (here_new >= here_old) {
                        /* Reading from the same stripe as writing to - bad */
                        printk(KERN_ERR "raid5: reshape_position too early for "
                               "auto-recovery - aborting.\n");
                        return -EINVAL;
                }
                printk(KERN_INFO "raid5: reshape will continue\n");
                /* OK, we should be able to continue; */
        } else {
                BUG_ON(mddev->level != mddev->new_level);
                BUG_ON(mddev->layout != mddev->new_layout);
                BUG_ON(mddev->chunk_size != mddev->new_chunk);
                BUG_ON(mddev->delta_disks != 0);
        }

        if (mddev->private == NULL)
                conf = setup_conf(mddev);
        else
                conf = mddev->private;

        if (IS_ERR(conf))
                return PTR_ERR(conf);

        mddev->thread = conf->thread;
        conf->thread = NULL;
        mddev->private = conf;

        /*
         * 0 for a fully functional array, 1 or 2 for a degraded array.
         */
        list_for_each_entry(rdev, &mddev->disks, same_set)
                if (rdev->raid_disk >= 0 &&
                    test_bit(In_sync, &rdev->flags))
                        working_disks++;

        mddev->degraded = conf->raid_disks - working_disks;

        if (mddev->degraded > conf->max_degraded) {
                printk(KERN_ERR "raid5: not enough operational devices for %s"
                        " (%d/%d failed)\n",
                        mdname(mddev), mddev->degraded, conf->raid_disks);
                goto abort;
        }

        /* device size must be a multiple of chunk size */
        mddev->dev_sectors &= ~(mddev->chunk_size / 512 - 1);
        mddev->resync_max_sectors = mddev->dev_sectors;

        if (mddev->degraded > 0 &&
            mddev->recovery_cp != MaxSector) {
                if (mddev->ok_start_degraded)
                        printk(KERN_WARNING
                               "raid5: starting dirty degraded array: %s"
                               "- data corruption possible.\n",
                               mdname(mddev));
                else {
                        printk(KERN_ERR
                               "raid5: cannot start dirty degraded array for %s\n",
                               mdname(mddev));
                        goto abort;
                }
        }

        if (mddev->degraded == 0)
                printk("raid5: raid level %d set %s active with %d out of %d"
                       " devices, algorithm %d\n", conf->level, mdname(mddev),
                       mddev->raid_disks-mddev->degraded, mddev->raid_disks,
                       mddev->new_layout);
        else
                printk(KERN_ALERT "raid5: raid level %d set %s active with %d"
                        " out of %d devices, algorithm %d\n", conf->level,
                        mdname(mddev), mddev->raid_disks - mddev->degraded,
                        mddev->raid_disks, mddev->new_layout);

        print_raid5_conf(conf);

        if (conf->reshape_progress != MaxSector) {
                printk("...ok start reshape thread\n");
                conf->reshape_safe = conf->reshape_progress;
                atomic_set(&conf->reshape_stripes, 0);
                clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
                clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
                set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
                set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
                mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                                                        "%s_reshape");
        }

        /* read-ahead size must cover two whole stripes, which is
         * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
         */
        {
                int data_disks = conf->previous_raid_disks - conf->max_degraded;
                int stripe = data_disks *
                        (mddev->chunk_size / PAGE_SIZE);
                if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                        mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
        }

        /* Ok, everything is just fine now */
        if (sysfs_create_group(&mddev->kobj, &raid5_attrs_group))
                printk(KERN_WARNING
                       "raid5: failed to create sysfs attributes for %s\n",
                       mdname(mddev));

        mddev->queue->queue_lock = &conf->device_lock;

        mddev->queue->unplug_fn = raid5_unplug_device;
        mddev->queue->backing_dev_info.congested_data = mddev;
        mddev->queue->backing_dev_info.congested_fn = raid5_congested;

        md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));

        blk_queue_merge_bvec(mddev->queue, raid5_mergeable_bvec);

        return 0;
abort:
        md_unregister_thread(mddev->thread);
        mddev->thread = NULL;
        if (conf) {
                shrink_stripes(conf);
                print_raid5_conf(conf);
                safe_put_page(conf->spare_page);
                kfree(conf->disks);
                kfree(conf->stripe_hashtbl);
                kfree(conf);
        }
        mddev->private = NULL;
        printk(KERN_ALERT "raid5: failed to run raid set %s\n", mdname(mddev));
        return -EIO;
}



static int stop(mddev_t *mddev)
{
        raid5_conf_t *conf = (raid5_conf_t *) mddev->private;

        md_unregister_thread(mddev->thread);
        mddev->thread = NULL;
        shrink_stripes(conf);
        kfree(conf->stripe_hashtbl);
        mddev->queue->backing_dev_info.congested_fn = NULL;
        blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
        sysfs_remove_group(&mddev->kobj, &raid5_attrs_group);
        kfree(conf->disks);
        kfree(conf);
        mddev->private = NULL;
        return 0;
}

#ifdef DEBUG
static void print_sh(struct seq_file *seq, struct stripe_head *sh)
{
        int i;

        seq_printf(seq, "sh %llu, pd_idx %d, state %ld.\n",
                   (unsigned long long)sh->sector, sh->pd_idx, sh->state);
        seq_printf(seq, "sh %llu,  count %d.\n",
                   (unsigned long long)sh->sector, atomic_read(&sh->count));
        seq_printf(seq, "sh %llu, ", (unsigned long long)sh->sector);
        for (i = 0; i < sh->disks; i++) {
                seq_printf(seq, "(cache%d: %p %ld) ",
                           i, sh->dev[i].page, sh->dev[i].flags);
        }
        seq_printf(seq, "\n");
}

static void printall(struct seq_file *seq, raid5_conf_t *conf)
{
        struct stripe_head *sh;
        struct hlist_node *hn;
        int i;

        spin_lock_irq(&conf->device_lock);
        for (i = 0; i < NR_HASH; i++) {
                hlist_for_each_entry(sh, hn, &conf->stripe_hashtbl[i], hash) {
                        if (sh->raid_conf != conf)
                                continue;
                        print_sh(seq, sh);
                }
        }
        spin_unlock_irq(&conf->device_lock);
}
#endif

static void status(struct seq_file *seq, mddev_t *mddev)
{
        raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
        int i;

        seq_printf (seq, " level %d, %dk chunk, algorithm %d", mddev->level, mddev->chunk_size >> 10, mddev->layout);
        seq_printf (seq, " [%d/%d] [", conf->raid_disks, conf->raid_disks - mddev->degraded);
        for (i = 0; i < conf->raid_disks; i++)
                seq_printf (seq, "%s",
                               conf->disks[i].rdev &&
                               test_bit(In_sync, &conf->disks[i].rdev->flags) ? "U" : "_");
        seq_printf (seq, "]");
#ifdef DEBUG
        seq_printf (seq, "\n");
        printall(seq, conf);
#endif
}

static void print_raid5_conf (raid5_conf_t *conf)
{
        int i;
        struct disk_info *tmp;

        printk("RAID5 conf printout:\n");
        if (!conf) {
                printk("(conf==NULL)\n");
                return;
        }
        printk(" --- rd:%d wd:%d\n", conf->raid_disks,
                 conf->raid_disks - conf->mddev->degraded);

        for (i = 0; i < conf->raid_disks; i++) {
                char b[BDEVNAME_SIZE];
                tmp = conf->disks + i;
                if (tmp->rdev)
                printk(" disk %d, o:%d, dev:%s\n",
                        i, !test_bit(Faulty, &tmp->rdev->flags),
                        bdevname(tmp->rdev->bdev,b));
        }
}

static int raid5_spare_active(mddev_t *mddev)
{
        int i;
        raid5_conf_t *conf = mddev->private;
        struct disk_info *tmp;

        for (i = 0; i < conf->raid_disks; i++) {
                tmp = conf->disks + i;
                if (tmp->rdev
                    && !test_bit(Faulty, &tmp->rdev->flags)
                    && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
                        unsigned long flags;
                        spin_lock_irqsave(&conf->device_lock, flags);
                        mddev->degraded--;
                        spin_unlock_irqrestore(&conf->device_lock, flags);
                }
        }
        print_raid5_conf(conf);
        return 0;
}

static int raid5_remove_disk(mddev_t *mddev, int number)
{
        raid5_conf_t *conf = mddev->private;
        int err = 0;
        mdk_rdev_t *rdev;
        struct disk_info *p = conf->disks + number;

        print_raid5_conf(conf);
        rdev = p->rdev;
        if (rdev) {
                if (number >= conf->raid_disks &&
                    conf->reshape_progress == MaxSector)
                        clear_bit(In_sync, &rdev->flags);

                if (test_bit(In_sync, &rdev->flags) ||
                    atomic_read(&rdev->nr_pending)) {
                        err = -EBUSY;
                        goto abort;
                }
                /* Only remove non-faulty devices if recovery
                 * isn't possible.
                 */
                if (!test_bit(Faulty, &rdev->flags) &&
                    mddev->degraded <= conf->max_degraded &&
                    number < conf->raid_disks) {
                        err = -EBUSY;
                        goto abort;
                }
                p->rdev = NULL;
                synchronize_rcu();
                if (atomic_read(&rdev->nr_pending)) {
                        /* lost the race, try later */
                        err = -EBUSY;
                        p->rdev = rdev;
                }
        }
abort:

        print_raid5_conf(conf);
        return err;
}

static int raid5_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
{
        raid5_conf_t *conf = mddev->private;
        int err = -EEXIST;
        int disk;
        struct disk_info *p;
        int first = 0;
        int last = conf->raid_disks - 1;

        if (mddev->degraded > conf->max_degraded)
                /* no point adding a device */
                return -EINVAL;

        if (rdev->raid_disk >= 0)
                first = last = rdev->raid_disk;

        /*
         * find the disk ... but prefer rdev->saved_raid_disk
         * if possible.
         */
        if (rdev->saved_raid_disk >= 0 &&
            rdev->saved_raid_disk >= first &&
            conf->disks[rdev->saved_raid_disk].rdev == NULL)
                disk = rdev->saved_raid_disk;
        else
                disk = first;
        for ( ; disk <= last ; disk++)
                if ((p=conf->disks + disk)->rdev == NULL) {
                        clear_bit(In_sync, &rdev->flags);
                        rdev->raid_disk = disk;
                        err = 0;
                        if (rdev->saved_raid_disk != disk)
                                conf->fullsync = 1;
                        rcu_assign_pointer(p->rdev, rdev);
                        break;
                }
        print_raid5_conf(conf);
        return err;
}

static int raid5_resize(mddev_t *mddev, sector_t sectors)
{
        /* no resync is happening, and there is enough space
         * on all devices, so we can resize.
         * We need to make sure resync covers any new space.
         * If the array is shrinking we should possibly wait until
         * any io in the removed space completes, but it hardly seems
         * worth it.
         */
        sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
        md_set_array_sectors(mddev, raid5_size(mddev, sectors,
                                               mddev->raid_disks));
        if (mddev->array_sectors >
            raid5_size(mddev, sectors, mddev->raid_disks))
                return -EINVAL;
        set_capacity(mddev->gendisk, mddev->array_sectors);
        mddev->changed = 1;
        if (sectors > mddev->dev_sectors && mddev->recovery_cp == MaxSector) {
                mddev->recovery_cp = mddev->dev_sectors;
                set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
        }
        mddev->dev_sectors = sectors;
        mddev->resync_max_sectors = sectors;
        return 0;
}

#ifdef CONFIG_MD_RAID5_RESHAPE
static int raid5_check_reshape(mddev_t *mddev)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);

        if (mddev->delta_disks == 0 &&
            mddev->new_layout == mddev->layout &&
            mddev->new_chunk == mddev->chunk_size)
                return -EINVAL; /* nothing to do */
        if (mddev->bitmap)
                /* Cannot grow a bitmap yet */
                return -EBUSY;
        if (mddev->degraded > conf->max_degraded)
                return -EINVAL;
        if (mddev->delta_disks < 0) {
                /* We might be able to shrink, but the devices must
                 * be made bigger first.
                 * For raid6, 4 is the minimum size.
                 * Otherwise 2 is the minimum
                 */
                int min = 2;
                if (mddev->level == 6)
                        min = 4;
                if (mddev->raid_disks + mddev->delta_disks < min)
                        return -EINVAL;
        }

        /* Can only proceed if there are plenty of stripe_heads.
         * We need a minimum of one full stripe,, and for sensible progress
         * it is best to have about 4 times that.
         * If we require 4 times, then the default 256 4K stripe_heads will
         * allow for chunk sizes up to 256K, which is probably OK.
         * If the chunk size is greater, user-space should request more
         * stripe_heads first.
         */
        if ((mddev->chunk_size / STRIPE_SIZE) * 4 > conf->max_nr_stripes ||
            (mddev->new_chunk / STRIPE_SIZE) * 4 > conf->max_nr_stripes) {
                printk(KERN_WARNING "raid5: reshape: not enough stripes.  Needed %lu\n",
                       (max(mddev->chunk_size, mddev->new_chunk)
                        / STRIPE_SIZE)*4);
                return -ENOSPC;
        }

        return resize_stripes(conf, conf->raid_disks + mddev->delta_disks);
}

static int raid5_start_reshape(mddev_t *mddev)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);
        mdk_rdev_t *rdev;
        int spares = 0;
        int added_devices = 0;
        unsigned long flags;

        if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
                return -EBUSY;

        list_for_each_entry(rdev, &mddev->disks, same_set)
                if (rdev->raid_disk < 0 &&
                    !test_bit(Faulty, &rdev->flags))
                        spares++;

        if (spares - mddev->degraded < mddev->delta_disks - conf->max_degraded)
                /* Not enough devices even to make a degraded array
                 * of that size
                 */
                return -EINVAL;

        /* Refuse to reduce size of the array.  Any reductions in
         * array size must be through explicit setting of array_size
         * attribute.
         */
        if (raid5_size(mddev, 0, conf->raid_disks + mddev->delta_disks)
            < mddev->array_sectors) {
                printk(KERN_ERR "md: %s: array size must be reduced "
                       "before number of disks\n", mdname(mddev));
                return -EINVAL;
        }

        atomic_set(&conf->reshape_stripes, 0);
        spin_lock_irq(&conf->device_lock);
        conf->previous_raid_disks = conf->raid_disks;
        conf->raid_disks += mddev->delta_disks;
        conf->prev_chunk = conf->chunk_size;
        conf->chunk_size = mddev->new_chunk;
        conf->prev_algo = conf->algorithm;
        conf->algorithm = mddev->new_layout;
        if (mddev->delta_disks < 0)
                conf->reshape_progress = raid5_size(mddev, 0, 0);
        else
                conf->reshape_progress = 0;
        conf->reshape_safe = conf->reshape_progress;
        conf->generation++;
        spin_unlock_irq(&conf->device_lock);

        /* Add some new drives, as many as will fit.
         * We know there are enough to make the newly sized array work.
         */
        list_for_each_entry(rdev, &mddev->disks, same_set)
                if (rdev->raid_disk < 0 &&
                    !test_bit(Faulty, &rdev->flags)) {
                        if (raid5_add_disk(mddev, rdev) == 0) {
                                char nm[20];
                                set_bit(In_sync, &rdev->flags);
                                added_devices++;
                                rdev->recovery_offset = 0;
                                sprintf(nm, "rd%d", rdev->raid_disk);
                                if (sysfs_create_link(&mddev->kobj,
                                                      &rdev->kobj, nm))
                                        printk(KERN_WARNING
                                               "raid5: failed to create "
                                               " link %s for %s\n",
                                               nm, mdname(mddev));
                        } else
                                break;
                }

        if (mddev->delta_disks > 0) {
                spin_lock_irqsave(&conf->device_lock, flags);
                mddev->degraded = (conf->raid_disks - conf->previous_raid_disks)
                        - added_devices;
                spin_unlock_irqrestore(&conf->device_lock, flags);
        }
        mddev->raid_disks = conf->raid_disks;
        mddev->reshape_position = 0;
        set_bit(MD_CHANGE_DEVS, &mddev->flags);

        clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
        clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
        set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
        set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
        mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                                                "%s_reshape");
        if (!mddev->sync_thread) {
                mddev->recovery = 0;
                spin_lock_irq(&conf->device_lock);
                mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
                conf->reshape_progress = MaxSector;
                spin_unlock_irq(&conf->device_lock);
                return -EAGAIN;
        }
        md_wakeup_thread(mddev->sync_thread);
        md_new_event(mddev);
        return 0;
}
#endif

/* This is called from the reshape thread and should make any
 * changes needed in 'conf'
 */
static void end_reshape(raid5_conf_t *conf)
{

        if (!test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery)) {

                spin_lock_irq(&conf->device_lock);
                conf->previous_raid_disks = conf->raid_disks;
                conf->reshape_progress = MaxSector;
                spin_unlock_irq(&conf->device_lock);

                /* read-ahead size must cover two whole stripes, which is
                 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
                 */
                {
                        int data_disks = conf->raid_disks - conf->max_degraded;
                        int stripe = data_disks * (conf->chunk_size
                                                   / PAGE_SIZE);
                        if (conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                                conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
                }
        }
}

/* This is called from the raid5d thread with mddev_lock held.
 * It makes config changes to the device.
 */
static void raid5_finish_reshape(mddev_t *mddev)
{
        struct block_device *bdev;
        raid5_conf_t *conf = mddev_to_conf(mddev);

        if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {

                if (mddev->delta_disks > 0) {
                        md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
                        set_capacity(mddev->gendisk, mddev->array_sectors);
                        mddev->changed = 1;

                        bdev = bdget_disk(mddev->gendisk, 0);
                        if (bdev) {
                                mutex_lock(&bdev->bd_inode->i_mutex);
                                i_size_write(bdev->bd_inode,
                                             (loff_t)mddev->array_sectors << 9);
                                mutex_unlock(&bdev->bd_inode->i_mutex);
                                bdput(bdev);
                        }
                } else {
                        int d;
                        mddev->degraded = conf->raid_disks;
                        for (d = 0; d < conf->raid_disks ; d++)
                                if (conf->disks[d].rdev &&
                                    test_bit(In_sync,
                                             &conf->disks[d].rdev->flags))
                                        mddev->degraded--;
                        for (d = conf->raid_disks ;
                             d < conf->raid_disks - mddev->delta_disks;
                             d++)
                                raid5_remove_disk(mddev, d);
                }
                mddev->layout = conf->algorithm;
                mddev->chunk_size = conf->chunk_size;
                mddev->reshape_position = MaxSector;
                mddev->delta_disks = 0;
        }
}

static void raid5_quiesce(mddev_t *mddev, int state)
{
        raid5_conf_t *conf = mddev_to_conf(mddev);

        switch(state) {
        case 2: /* resume for a suspend */
                wake_up(&conf->wait_for_overlap);
                break;

        case 1: /* stop all writes */
                spin_lock_irq(&conf->device_lock);
                conf->quiesce = 1;
                wait_event_lock_irq(conf->wait_for_stripe,
                                    atomic_read(&conf->active_stripes) == 0 &&
                                    atomic_read(&conf->active_aligned_reads) == 0,
                                    conf->device_lock, /* nothing */);
                spin_unlock_irq(&conf->device_lock);
                break;

        case 0: /* re-enable writes */
                spin_lock_irq(&conf->device_lock);
                conf->quiesce = 0;
                wake_up(&conf->wait_for_stripe);
                wake_up(&conf->wait_for_overlap);
                spin_unlock_irq(&conf->device_lock);
                break;
        }
}


static void *raid5_takeover_raid1(mddev_t *mddev)
{
        int chunksect;

        if (mddev->raid_disks != 2 ||
            mddev->degraded > 1)
                return ERR_PTR(-EINVAL);

        /* Should check if there are write-behind devices? */

        chunksect = 64*2; /* 64K by default */

        /* The array must be an exact multiple of chunksize */
        while (chunksect && (mddev->array_sectors & (chunksect-1)))
                chunksect >>= 1;

        if ((chunksect<<9) < STRIPE_SIZE)
                /* array size does not allow a suitable chunk size */
                return ERR_PTR(-EINVAL);

        mddev->new_level = 5;
        mddev->new_layout = ALGORITHM_LEFT_SYMMETRIC;
        mddev->new_chunk = chunksect << 9;

        return setup_conf(mddev);
}

static void *raid5_takeover_raid6(mddev_t *mddev)
{
        int new_layout;

        switch (mddev->layout) {
        case ALGORITHM_LEFT_ASYMMETRIC_6:
                new_layout = ALGORITHM_LEFT_ASYMMETRIC;
                break;
        case ALGORITHM_RIGHT_ASYMMETRIC_6:
                new_layout = ALGORITHM_RIGHT_ASYMMETRIC;
                break;
        case ALGORITHM_LEFT_SYMMETRIC_6:
                new_layout = ALGORITHM_LEFT_SYMMETRIC;
                break;
        case ALGORITHM_RIGHT_SYMMETRIC_6:
                new_layout = ALGORITHM_RIGHT_SYMMETRIC;
                break;
        case ALGORITHM_PARITY_0_6:
                new_layout = ALGORITHM_PARITY_0;
                break;
        case ALGORITHM_PARITY_N:
                new_layout = ALGORITHM_PARITY_N;
                break;
        default:
                return ERR_PTR(-EINVAL);
        }
        mddev->new_level = 5;
        mddev->new_layout = new_layout;
        mddev->delta_disks = -1;
        mddev->raid_disks -= 1;
        return setup_conf(mddev);
}


static int raid5_reconfig(mddev_t *mddev, int new_layout, int new_chunk)
{
        /* For a 2-drive array, the layout and chunk size can be changed
         * immediately as not restriping is needed.
         * For larger arrays we record the new value - after validation
         * to be used by a reshape pass.
         */
        raid5_conf_t *conf = mddev_to_conf(mddev);

        if (new_layout >= 0 && !algorithm_valid_raid5(new_layout))
                return -EINVAL;
        if (new_chunk > 0) {
                if (new_chunk & (new_chunk-1))
                        /* not a power of 2 */
                        return -EINVAL;
                if (new_chunk < PAGE_SIZE)
                        return -EINVAL;
                if (mddev->array_sectors & ((new_chunk>>9)-1))
                        /* not factor of array size */
                        return -EINVAL;
        }

        /* They look valid */

        if (mddev->raid_disks == 2) {

                if (new_layout >= 0) {
                        conf->algorithm = new_layout;
                        mddev->layout = mddev->new_layout = new_layout;
                }
                if (new_chunk > 0) {
                        conf->chunk_size = new_chunk;
                        mddev->chunk_size = mddev->new_chunk = new_chunk;
                }
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
        } else {
                if (new_layout >= 0)
                        mddev->new_layout = new_layout;
                if (new_chunk > 0)
                        mddev->new_chunk = new_chunk;
        }
        return 0;
}

static int raid6_reconfig(mddev_t *mddev, int new_layout, int new_chunk)
{
        if (new_layout >= 0 && !algorithm_valid_raid6(new_layout))
                return -EINVAL;
        if (new_chunk > 0) {
                if (new_chunk & (new_chunk-1))
                        /* not a power of 2 */
                        return -EINVAL;
                if (new_chunk < PAGE_SIZE)
                        return -EINVAL;
                if (mddev->array_sectors & ((new_chunk>>9)-1))
                        /* not factor of array size */
                        return -EINVAL;
        }

        /* They look valid */

        if (new_layout >= 0)
                mddev->new_layout = new_layout;
        if (new_chunk > 0)
                mddev->new_chunk = new_chunk;

        return 0;
}

static void *raid5_takeover(mddev_t *mddev)
{
        /* raid5 can take over:
         *  raid0 - if all devices are the same - make it a raid4 layout
         *  raid1 - if there are two drives.  We need to know the chunk size
         *  raid4 - trivial - just use a raid4 layout.
         *  raid6 - Providing it is a *_6 layout
         *
         * For now, just do raid1
         */

        if (mddev->level == 1)
                return raid5_takeover_raid1(mddev);
        if (mddev->level == 4) {
                mddev->new_layout = ALGORITHM_PARITY_N;
                mddev->new_level = 5;
                return setup_conf(mddev);
        }
        if (mddev->level == 6)
                return raid5_takeover_raid6(mddev);

        return ERR_PTR(-EINVAL);
}


static struct mdk_personality raid5_personality;

static void *raid6_takeover(mddev_t *mddev)
{
        /* Currently can only take over a raid5.  We map the
         * personality to an equivalent raid6 personality
         * with the Q block at the end.
         */
        int new_layout;

        if (mddev->pers != &raid5_personality)
                return ERR_PTR(-EINVAL);
        if (mddev->degraded > 1)
                return ERR_PTR(-EINVAL);
        if (mddev->raid_disks > 253)
                return ERR_PTR(-EINVAL);
        if (mddev->raid_disks < 3)
                return ERR_PTR(-EINVAL);

        switch (mddev->layout) {
        case ALGORITHM_LEFT_ASYMMETRIC:
                new_layout = ALGORITHM_LEFT_ASYMMETRIC_6;
                break;
        case ALGORITHM_RIGHT_ASYMMETRIC:
                new_layout = ALGORITHM_RIGHT_ASYMMETRIC_6;
                break;
        case ALGORITHM_LEFT_SYMMETRIC:
                new_layout = ALGORITHM_LEFT_SYMMETRIC_6;
                break;
        case ALGORITHM_RIGHT_SYMMETRIC:
                new_layout = ALGORITHM_RIGHT_SYMMETRIC_6;
                break;
        case ALGORITHM_PARITY_0:
                new_layout = ALGORITHM_PARITY_0_6;
                break;
        case ALGORITHM_PARITY_N:
                new_layout = ALGORITHM_PARITY_N;
                break;
        default:
                return ERR_PTR(-EINVAL);
        }
        mddev->new_level = 6;
        mddev->new_layout = new_layout;
        mddev->delta_disks = 1;
        mddev->raid_disks += 1;
        return setup_conf(mddev);
}


static struct mdk_personality raid6_personality =
{
        .name           = "raid6",
        .level          = 6,
        .owner          = THIS_MODULE,
        .make_request   = make_request,
        .run            = run,
        .stop           = stop,
        .status         = status,
        .error_handler  = error,
        .hot_add_disk   = raid5_add_disk,
        .hot_remove_disk= raid5_remove_disk,
        .spare_active   = raid5_spare_active,
        .sync_request   = sync_request,
        .resize         = raid5_resize,
        .size           = raid5_size,
#ifdef CONFIG_MD_RAID5_RESHAPE
        .check_reshape  = raid5_check_reshape,
        .start_reshape  = raid5_start_reshape,
        .finish_reshape = raid5_finish_reshape,
#endif
        .quiesce        = raid5_quiesce,
        .takeover       = raid6_takeover,
        .reconfig       = raid6_reconfig,
};
static struct mdk_personality raid5_personality =
{
        .name           = "raid5",
        .level          = 5,
        .owner          = THIS_MODULE,
        .make_request   = make_request,
        .run            = run,
        .stop           = stop,
        .status         = status,
        .error_handler  = error,
        .hot_add_disk   = raid5_add_disk,
        .hot_remove_disk= raid5_remove_disk,
        .spare_active   = raid5_spare_active,
        .sync_request   = sync_request,
        .resize         = raid5_resize,
        .size           = raid5_size,
#ifdef CONFIG_MD_RAID5_RESHAPE
        .check_reshape  = raid5_check_reshape,
        .start_reshape  = raid5_start_reshape,
        .finish_reshape = raid5_finish_reshape,
#endif
        .quiesce        = raid5_quiesce,
        .takeover       = raid5_takeover,
        .reconfig       = raid5_reconfig,
};

static struct mdk_personality raid4_personality =
{
        .name           = "raid4",
        .level          = 4,
        .owner          = THIS_MODULE,
        .make_request   = make_request,
        .run            = run,
        .stop           = stop,
        .status         = status,
        .error_handler  = error,
        .hot_add_disk   = raid5_add_disk,
        .hot_remove_disk= raid5_remove_disk,
        .spare_active   = raid5_spare_active,
        .sync_request   = sync_request,
        .resize         = raid5_resize,
        .size           = raid5_size,
#ifdef CONFIG_MD_RAID5_RESHAPE
        .check_reshape  = raid5_check_reshape,
        .start_reshape  = raid5_start_reshape,
        .finish_reshape = raid5_finish_reshape,
#endif
        .quiesce        = raid5_quiesce,
};

static int __init raid5_init(void)
{
        register_md_personality(&raid6_personality);
        register_md_personality(&raid5_personality);
        register_md_personality(&raid4_personality);
        return 0;
}

static void raid5_exit(void)
{
        unregister_md_personality(&raid6_personality);
        unregister_md_personality(&raid5_personality);
        unregister_md_personality(&raid4_personality);
}

module_init(raid5_init);
module_exit(raid5_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS("md-personality-4"); /* RAID5 */
MODULE_ALIAS("md-raid5");
MODULE_ALIAS("md-raid4");
MODULE_ALIAS("md-level-5");
MODULE_ALIAS("md-level-4");
MODULE_ALIAS("md-personality-8"); /* RAID6 */
MODULE_ALIAS("md-raid6");
MODULE_ALIAS("md-level-6");

/* This used to be two separate modules, they were: */
MODULE_ALIAS("raid5");
MODULE_ALIAS("raid6");