[PATCH] md: count corrected read errors per drive

[safe/jmp/linux-2.6] / drivers / md / raid6main.c

/*
 * raid6main.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-6 management functions.  This code is derived from raid5.c.
 * Last merge from raid5.c bkcvs version 1.79 (kernel 2.6.1).
 *
 * 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.
 */


#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/bitops.h>
#include <asm/atomic.h>
#include "raid6.h"

#include <linux/raid/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 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 RAID6_DEBUG     0       /* Extremely verbose printk */
#define RAID6_PARANOIA  1       /* Check spinlocks */
#define RAID6_DUMPSTATE 0       /* Include stripe cache state in /proc/mdstat */
#if RAID6_PARANOIA && defined(CONFIG_SMP)
# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
#else
# define CHECK_DEVLOCK()
#endif

#define PRINTK(x...) ((void)(RAID6_DEBUG && printk(KERN_DEBUG x)))
#if RAID6_DEBUG
#undef inline
#undef __inline__
#define inline
#define __inline__
#endif

#if !RAID6_USE_EMPTY_ZERO_PAGE
/* In .bss so it's zeroed */
const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(256)));
#endif

static inline int raid6_next_disk(int disk, int raid_disks)
{
        disk++;
        return (disk < raid_disks) ? disk : 0;
}

static void print_raid6_conf (raid6_conf_t *conf);

static inline void __release_stripe(raid6_conf_t *conf, struct stripe_head *sh)
{
        if (atomic_dec_and_test(&sh->count)) {
                if (!list_empty(&sh->lru))
                        BUG();
                if (atomic_read(&conf->active_stripes)==0)
                        BUG();
                if (test_bit(STRIPE_HANDLE, &sh->state)) {
                        if (test_bit(STRIPE_DELAYED, &sh->state))
                                list_add_tail(&sh->lru, &conf->delayed_list);
                        else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
                                 conf->seq_write == sh->bm_seq)
                                list_add_tail(&sh->lru, &conf->bitmap_list);
                        else {
                                clear_bit(STRIPE_BIT_DELAY, &sh->state);
                                list_add_tail(&sh->lru, &conf->handle_list);
                        }
                        md_wakeup_thread(conf->mddev->thread);
                } else {
                        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);
                        }
                        list_add_tail(&sh->lru, &conf->inactive_list);
                        atomic_dec(&conf->active_stripes);
                        if (!conf->inactive_blocked ||
                            atomic_read(&conf->active_stripes) < (NR_STRIPES*3/4))
                                wake_up(&conf->wait_for_stripe);
                }
        }
}
static void release_stripe(struct stripe_head *sh)
{
        raid6_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)
{
        PRINTK("remove_hash(), stripe %llu\n", (unsigned long long)sh->sector);

        hlist_del_init(&sh->hash);
}

static inline void insert_hash(raid6_conf_t *conf, struct stripe_head *sh)
{
        struct hlist_head *hp = stripe_hash(conf, sh->sector);

        PRINTK("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(raid6_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 raid6_build_block (struct stripe_head *sh, int i);

static inline void init_stripe(struct stripe_head *sh, sector_t sector, int pd_idx)
{
        raid6_conf_t *conf = sh->raid_conf;
        int disks = conf->raid_disks, i;

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

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

        remove_hash(sh);

        sh->sector = sector;
        sh->pd_idx = pd_idx;
        sh->state = 0;

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

                if (dev->toread || dev->towrite || dev->written ||
                    test_bit(R5_LOCKED, &dev->flags)) {
                        PRINTK("sector=%llx i=%d %p %p %p %d\n",
                               (unsigned long long)sh->sector, i, dev->toread,
                               dev->towrite, dev->written,
                               test_bit(R5_LOCKED, &dev->flags));
                        BUG();
                }
                dev->flags = 0;
                raid6_build_block(sh, i);
        }
        insert_hash(conf, sh);
}

static struct stripe_head *__find_stripe(raid6_conf_t *conf, sector_t sector)
{
        struct stripe_head *sh;
        struct hlist_node *hn;

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

static void unplug_slaves(mddev_t *mddev);

static struct stripe_head *get_active_stripe(raid6_conf_t *conf, sector_t sector,
                                             int pd_idx, int noblock)
{
        struct stripe_head *sh;

        PRINTK("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);
                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) < (NR_STRIPES *3/4)
                                                     || !conf->inactive_blocked),
                                                    conf->device_lock,
                                                    unplug_slaves(conf->mddev);
                                        );
                                conf->inactive_blocked = 0;
                        } else
                                init_stripe(sh, sector, pd_idx);
                } else {
                        if (atomic_read(&sh->count)) {
                                if (!list_empty(&sh->lru))
                                        BUG();
                        } else {
                                if (!test_bit(STRIPE_HANDLE, &sh->state))
                                        atomic_inc(&conf->active_stripes);
                                if (list_empty(&sh->lru))
                                        BUG();
                                list_del_init(&sh->lru);
                        }
                }
        } while (sh == NULL);

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

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

static int grow_stripes(raid6_conf_t *conf, int num)
{
        struct stripe_head *sh;
        kmem_cache_t *sc;
        int devs = conf->raid_disks;

        sprintf(conf->cache_name, "raid6/%s", mdname(conf->mddev));

        sc = kmem_cache_create(conf->cache_name,
                               sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
                               0, 0, NULL, NULL);
        if (!sc)
                return 1;
        conf->slab_cache = sc;
        while (num--) {
                sh = kmem_cache_alloc(sc, GFP_KERNEL);
                if (!sh)
                        return 1;
                memset(sh, 0, sizeof(*sh) + (devs-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(sc, sh);
                        return 1;
                }
                /* 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 0;
}

static void shrink_stripes(raid6_conf_t *conf)
{
        struct stripe_head *sh;

        while (1) {
                spin_lock_irq(&conf->device_lock);
                sh = get_free_stripe(conf);
                spin_unlock_irq(&conf->device_lock);
                if (!sh)
                        break;
                if (atomic_read(&sh->count))
                        BUG();
                shrink_buffers(sh, conf->raid_disks);
                kmem_cache_free(conf->slab_cache, sh);
                atomic_dec(&conf->active_stripes);
        }
        kmem_cache_destroy(conf->slab_cache);
        conf->slab_cache = NULL;
}

static int raid6_end_read_request(struct bio * bi, unsigned int bytes_done,
                                  int error)
{
        struct stripe_head *sh = bi->bi_private;
        raid6_conf_t *conf = sh->raid_conf;
        int disks = conf->raid_disks, i;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);

        if (bi->bi_size)
                return 1;

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

        PRINTK("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 0;
        }

        if (uptodate) {
#if 0
                struct bio *bio;
                unsigned long flags;
                spin_lock_irqsave(&conf->device_lock, flags);
                /* we can return a buffer if we bypassed the cache or
                 * if the top buffer is not in highmem.  If there are
                 * multiple buffers, leave the extra work to
                 * handle_stripe
                 */
                buffer = sh->bh_read[i];
                if (buffer &&
                    (!PageHighMem(buffer->b_page)
                     || buffer->b_page == bh->b_page )
                        ) {
                        sh->bh_read[i] = buffer->b_reqnext;
                        buffer->b_reqnext = NULL;
                } else
                        buffer = NULL;
                spin_unlock_irqrestore(&conf->device_lock, flags);
                if (sh->bh_page[i]==bh->b_page)
                        set_buffer_uptodate(bh);
                if (buffer) {
                        if (buffer->b_page != bh->b_page)
                                memcpy(buffer->b_data, bh->b_data, bh->b_size);
                        buffer->b_end_io(buffer, 1);
                }
#else
                set_bit(R5_UPTODATE, &sh->dev[i].flags);
#endif
                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        printk(KERN_INFO "raid6: read error corrected!!\n");
                        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 {
                int retry = 0;
                clear_bit(R5_UPTODATE, &sh->dev[i].flags);
                atomic_inc(&conf->disks[i].rdev->read_errors);
                if (conf->mddev->degraded)
                        printk(KERN_WARNING "raid6: read error not correctable.\n");
                else if (test_bit(R5_ReWrite, &sh->dev[i].flags))
                        /* Oh, no!!! */
                        printk(KERN_WARNING "raid6: read error NOT corrected!!\n");
                else if (atomic_read(&conf->disks[i].rdev->read_errors)
                         > conf->max_nr_stripes)
                        printk(KERN_WARNING
                               "raid6: Too many read errors, failing device.\n");
                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, conf->disks[i].rdev);
                }
        }
        rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
#if 0
        /* must restore b_page before unlocking buffer... */
        if (sh->bh_page[i] != bh->b_page) {
                bh->b_page = sh->bh_page[i];
                bh->b_data = page_address(bh->b_page);
                clear_buffer_uptodate(bh);
        }
#endif
        clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
        return 0;
}

static int raid6_end_write_request (struct bio *bi, unsigned int bytes_done,
                                    int error)
{
        struct stripe_head *sh = bi->bi_private;
        raid6_conf_t *conf = sh->raid_conf;
        int disks = conf->raid_disks, i;
        unsigned long flags;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);

        if (bi->bi_size)
                return 1;

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

        PRINTK("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 0;
        }

        spin_lock_irqsave(&conf->device_lock, flags);
        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(conf, sh);
        spin_unlock_irqrestore(&conf->device_lock, flags);
        return 0;
}


static sector_t compute_blocknr(struct stripe_head *sh, int i);

static void raid6_build_block (struct stripe_head *sh, int i)
{
        struct r5dev *dev = &sh->dev[i];
        int pd_idx = sh->pd_idx;
        int qd_idx = raid6_next_disk(pd_idx, sh->raid_conf->raid_disks);

        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;
        if (i != pd_idx && i != qd_idx)
                dev->sector = compute_blocknr(sh, i);
}

static void error(mddev_t *mddev, mdk_rdev_t *rdev)
{
        char b[BDEVNAME_SIZE];
        raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
        PRINTK("raid6: error called\n");

        if (!test_bit(Faulty, &rdev->flags)) {
                mddev->sb_dirty = 1;
                if (test_bit(In_sync, &rdev->flags)) {
                        conf->working_disks--;
                        mddev->degraded++;
                        conf->failed_disks++;
                        clear_bit(In_sync, &rdev->flags);
                        /*
                         * if recovery was running, make sure it aborts.
                         */
                        set_bit(MD_RECOVERY_ERR, &mddev->recovery);
                }
                set_bit(Faulty, &rdev->flags);
                printk (KERN_ALERT
                        "raid6: Disk failure on %s, disabling device."
                        " Operation continuing on %d devices\n",
                        bdevname(rdev->bdev,b), conf->working_disks);
        }
}

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
static sector_t raid6_compute_sector(sector_t r_sector, unsigned int raid_disks,
                        unsigned int data_disks, unsigned int * dd_idx,
                        unsigned int * pd_idx, raid6_conf_t *conf)
{
        long stripe;
        unsigned long chunk_number;
        unsigned int chunk_offset;
        sector_t new_sector;
        int sectors_per_chunk = conf->chunk_size >> 9;

        /* 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;
        if ( r_sector != chunk_number ) {
                printk(KERN_CRIT "raid6: ERROR: r_sector = %llu, chunk_number = %lu\n",
                       (unsigned long long)r_sector, (unsigned long)chunk_number);
                BUG();
        }

        /*
         * 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.
         */

        /**** FIX THIS ****/
        switch (conf->algorithm) {
        case ALGORITHM_LEFT_ASYMMETRIC:
                *pd_idx = raid_disks - 1 - (stripe % raid_disks);
                if (*pd_idx == raid_disks-1)
                        (*dd_idx)++;    /* Q D D D P */
                else if (*dd_idx >= *pd_idx)
                        (*dd_idx) += 2; /* D D P Q D */
                break;
        case ALGORITHM_RIGHT_ASYMMETRIC:
                *pd_idx = stripe % raid_disks;
                if (*pd_idx == raid_disks-1)
                        (*dd_idx)++;    /* Q D D D P */
                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);
                *dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
                break;
        case ALGORITHM_RIGHT_SYMMETRIC:
                *pd_idx = stripe % raid_disks;
                *dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
                break;
        default:
                printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
                        conf->algorithm);
        }

        PRINTK("raid6: chunk_number = %lu, pd_idx = %u, dd_idx = %u\n",
               chunk_number, *pd_idx, *dd_idx);

        /*
         * 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)
{
        raid6_conf_t *conf = sh->raid_conf;
        int raid_disks = conf->raid_disks, data_disks = raid_disks - 2;
        sector_t new_sector = sh->sector, check;
        int sectors_per_chunk = conf->chunk_size >> 9;
        sector_t stripe;
        int chunk_offset;
        int chunk_number, dummy1, dummy2, dd_idx = i;
        sector_t r_sector;
        int i0 = i;

        chunk_offset = sector_div(new_sector, sectors_per_chunk);
        stripe = new_sector;
        if ( new_sector != stripe ) {
                printk(KERN_CRIT "raid6: ERROR: new_sector = %llu, stripe = %lu\n",
                       (unsigned long long)new_sector, (unsigned long)stripe);
                BUG();
        }

        switch (conf->algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        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;
                default:
                        printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
                                conf->algorithm);
        }

        PRINTK("raid6: compute_blocknr: pd_idx = %u, i0 = %u, i = %u\n", sh->pd_idx, i0, i);

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

        check = raid6_compute_sector (r_sector, raid_disks, data_disks, &dummy1, &dummy2, conf);
        if (check != sh->sector || dummy1 != dd_idx || dummy2 != sh->pd_idx) {
                printk(KERN_CRIT "raid6: 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_block(count, STRIPE_SIZE, ptr);     \
                                count = 1;                              \
                           }                                            \
                        } while(0)

/* Compute P and Q syndromes */
static void compute_parity(struct stripe_head *sh, int method)
{
        raid6_conf_t *conf = sh->raid_conf;
        int i, pd_idx = sh->pd_idx, qd_idx, d0_idx, disks = conf->raid_disks, count;
        struct bio *chosen;
        /**** FIX THIS: This could be very bad if disks is close to 256 ****/
        void *ptrs[disks];

        qd_idx = raid6_next_disk(pd_idx, disks);
        d0_idx = raid6_next_disk(qd_idx, disks);

        PRINTK("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);

                                if (sh->dev[i].written) BUG();
                                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);
                }

//      switch(method) {
//      case RECONSTRUCT_WRITE:
//      case CHECK_PARITY:
//      case UPDATE_PARITY:
                /* Note that unlike RAID-5, the ordering of the disks matters greatly. */
                /* FIX: Is this ordering of drives even remotely optimal? */
                count = 0;
                i = d0_idx;
                do {
                        ptrs[count++] = page_address(sh->dev[i].page);
                        if (count <= disks-2 && !test_bit(R5_UPTODATE, &sh->dev[i].flags))
                                printk("block %d/%d not uptodate on parity calc\n", i,count);
                        i = raid6_next_disk(i, disks);
                } while ( i != d0_idx );
//              break;
//      }

        raid6_call.gen_syndrome(disks, 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)
{
        raid6_conf_t *conf = sh->raid_conf;
        int i, count, disks = conf->raid_disks;
        void *ptr[MAX_XOR_BLOCKS], *p;
        int pd_idx = sh->pd_idx;
        int qd_idx = raid6_next_disk(pd_idx, disks);

        PRINTK("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_parity(sh, UPDATE_PARITY);
        } else {
                ptr[0] = page_address(sh->dev[dd_idx].page);
                if (!nozero) memset(ptr[0], 0, STRIPE_SIZE);
                count = 1;
                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 != 1)
                        xor_block(count, STRIPE_SIZE, 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)
{
        raid6_conf_t *conf = sh->raid_conf;
        int i, count, disks = conf->raid_disks;
        int pd_idx = sh->pd_idx;
        int qd_idx = raid6_next_disk(pd_idx, disks);
        int d0_idx = raid6_next_disk(qd_idx, disks);
        int faila, failb;

        /* faila and failb are disk numbers relative to d0_idx */
        /* pd_idx become disks-2 and qd_idx become disks-1 */
        faila = (dd_idx1 < d0_idx) ? dd_idx1+(disks-d0_idx) : dd_idx1-d0_idx;
        failb = (dd_idx2 < d0_idx) ? dd_idx2+(disks-d0_idx) : dd_idx2-d0_idx;

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

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

        if ( failb == disks-1 ) {
                /* Q disk is one of the missing disks */
                if ( faila == disks-2 ) {
                        /* Missing P+Q, just recompute */
                        compute_parity(sh, UPDATE_PARITY);
                        return;
                } else {
                        /* We're missing D+Q; recompute D from P */
                        compute_block_1(sh, (dd_idx1 == qd_idx) ? dd_idx2 : dd_idx1, 0);
                        compute_parity(sh, UPDATE_PARITY); /* Is this necessary? */
                        return;
                }
        }

        /* We're missing D+P or D+D; build pointer table */
        {
                /**** FIX THIS: This could be very bad if disks is close to 256 ****/
                void *ptrs[disks];

                count = 0;
                i = d0_idx;
                do {
                        ptrs[count++] = page_address(sh->dev[i].page);
                        i = raid6_next_disk(i, disks);
                        if (i != dd_idx1 && i != dd_idx2 &&
                            !test_bit(R5_UPTODATE, &sh->dev[i].flags))
                                printk("compute_2 with missing block %d/%d\n", count, i);
                } while ( i != d0_idx );

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


/*
 * 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;
        raid6_conf_t *conf = sh->raid_conf;
        int firstwrite=0;

        PRINTK("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;

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

        PRINTK("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) {
                sh->bm_seq = conf->seq_write;
                bitmap_startwrite(conf->mddev->bitmap, sh->sector,
                                  STRIPE_SECTORS, 0);
                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 int page_is_zero(struct page *p)
{
        char *a = page_address(p);
        return ((*(u32*)a) == 0 &&
                memcmp(a, a+4, STRIPE_SIZE-4)==0);
}
/*
 * 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
 *
 * Parity calculations are done inside the stripe lock
 * buffers are taken off read_list or write_list, and bh_cache buffers
 * get BH_Lock set before the stripe lock is released.
 *
 */

static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
{
        raid6_conf_t *conf = sh->raid_conf;
        int disks = conf->raid_disks;
        struct bio *return_bi= NULL;
        struct bio *bi;
        int i;
        int syncing;
        int locked=0, uptodate=0, to_read=0, to_write=0, failed=0, written=0;
        int non_overwrite = 0;
        int failed_num[2] = {0, 0};
        struct r5dev *dev, *pdev, *qdev;
        int pd_idx = sh->pd_idx;
        int qd_idx = raid6_next_disk(pd_idx, disks);
        int p_failed, q_failed;

        PRINTK("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);

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

        syncing = test_bit(STRIPE_SYNCING, &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);

                PRINTK("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;
                        PRINTK("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 (--rbi->bi_phys_segments == 0) {
                                        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)) locked++;
                if (test_bit(R5_UPTODATE, &dev->flags)) uptodate++;


                if (dev->toread) to_read++;
                if (dev->towrite) {
                        to_write++;
                        if (!test_bit(R5_OVERWRITE, &dev->flags))
                                non_overwrite++;
                }
                if (dev->written) written++;
                rdev = rcu_dereference(conf->disks[i].rdev);
                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 ( failed < 2 )
                                failed_num[failed] = i;
                        failed++;
                } else
                        set_bit(R5_Insync, &dev->flags);
        }
        rcu_read_unlock();
        PRINTK("locked=%d uptodate=%d to_read=%d"
               " to_write=%d failed=%d failed_num=%d,%d\n",
               locked, uptodate, to_read, to_write, failed,
               failed_num[0], failed_num[1]);
        /* check if the array has lost >2 devices and, if so, some requests might
         * need to be failed
         */
        if (failed > 2 && to_read+to_write+written) {
                for (i=disks; i--; ) {
                        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) { 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 (--bi->bi_phys_segments == 0) {
                                        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 (--bi->bi_phys_segments == 0) {
                                        md_write_end(conf->mddev);
                                        bi->bi_next = return_bi;
                                        return_bi = bi;
                                }
                                bi = bi2;
                        }

                        /* fail any reads if this device is non-operational */
                        if (!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) 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 (--bi->bi_phys_segments == 0) {
                                                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 (failed > 2 && syncing) {
                md_done_sync(conf->mddev, STRIPE_SECTORS,0);
                clear_bit(STRIPE_SYNCING, &sh->state);
                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];
        p_failed = (failed >= 1 && failed_num[0] == pd_idx)
                || (failed >= 2 && failed_num[1] == pd_idx);
        qdev = &sh->dev[qd_idx];
        q_failed = (failed >= 1 && failed_num[0] == qd_idx)
                || (failed >= 2 && failed_num[1] == qd_idx);

        if ( written &&
             ( p_failed || ((test_bit(R5_Insync, &pdev->flags)
                             && !test_bit(R5_LOCKED, &pdev->flags)
                             && test_bit(R5_UPTODATE, &pdev->flags))) ) &&
             ( q_failed || ((test_bit(R5_Insync, &qdev->flags)
                             && !test_bit(R5_LOCKED, &qdev->flags)
                             && test_bit(R5_UPTODATE, &qdev->flags))) ) ) {
                /* 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.
                 */
                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 */
                                        int bitmap_end = 0;
                                        struct bio *wbi, *wbi2;
                                        PRINTK("Return write for stripe %llu disc %d\n",
                                               (unsigned long long)sh->sector, 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 (--wbi->bi_phys_segments == 0) {
                                                        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);
                                }
                        }
        }

        /* 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 (to_read || non_overwrite || (to_write && failed) || (syncing && (uptodate < disks))) {
                for (i=disks; i--;) {
                        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)) ||
                             syncing ||
                             (failed >= 1 && (sh->dev[failed_num[0]].toread || to_write)) ||
                             (failed >= 2 && (sh->dev[failed_num[1]].toread || to_write))
                                    )
                                ) {
                                /* we would like to get this block, possibly
                                 * by computing it, but we might not be able to
                                 */
                                if (uptodate == disks-1) {
                                        PRINTK("Computing stripe %llu block %d\n",
                                               (unsigned long long)sh->sector, i);
                                        compute_block_1(sh, i, 0);
                                        uptodate++;
                                } else if ( uptodate == disks-2 && 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);
                                        PRINTK("Computing stripe %llu blocks %d,%d\n",
                                               (unsigned long long)sh->sector, i, other);
                                        compute_block_2(sh, i, other);
                                        uptodate += 2;
                                } else if (test_bit(R5_Insync, &dev->flags)) {
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
#if 0
                                        /* if I am just reading this block and we don't have
                                           a failed drive, or any pending writes then sidestep the cache */
                                        if (sh->bh_read[i] && !sh->bh_read[i]->b_reqnext &&
                                            ! syncing && !failed && !to_write) {
                                                sh->bh_cache[i]->b_page =  sh->bh_read[i]->b_page;
                                                sh->bh_cache[i]->b_data =  sh->bh_read[i]->b_data;
                                        }
#endif
                                        locked++;
                                        PRINTK("Reading block %d (sync=%d)\n",
                                                i, syncing);
                                }
                        }
                }
                set_bit(STRIPE_HANDLE, &sh->state);
        }

        /* now to consider writing and what else, if anything should be read */
        if (to_write) {
                int rcw=0, must_compute=0;
                for (i=disks ; i--;) {
                        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)
#if 0
                                || sh->bh_page[i] != bh->b_page
#endif
                                    ) &&
                            !test_bit(R5_UPTODATE, &dev->flags)) {
                                if (test_bit(R5_Insync, &dev->flags)) rcw++;
                                else {
                                        PRINTK("raid6: must_compute: disk %d flags=%#lx\n", i, dev->flags);
                                        must_compute++;
                                }
                        }
                }
                PRINTK("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--;) {
                                dev = &sh->dev[i];
                                if (!test_bit(R5_OVERWRITE, &dev->flags)
                                    && !(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))
                                        {
                                                PRINTK("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);
                                                locked++;
                                        } else {
                                                PRINTK("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 (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 ( failed ) {
                                case 0: BUG();
                                case 1: compute_block_1(sh, failed_num[0], 0); break;
                                case 2: compute_block_2(sh, failed_num[0], failed_num[1]); break;
                                default: BUG(); /* This request should have been failed? */
                                }
                        }

                        PRINTK("Computing parity for stripe %llu\n", (unsigned long long)sh->sector);
                        compute_parity(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)) {
                                        PRINTK("Writing stripe %llu block %d\n",
                                               (unsigned long long)sh->sector, i);
                                        locked++;
                                        set_bit(R5_Wantwrite, &sh->dev[i].flags);
                                }
                        /* 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);
                        }
                }
        }

        /* 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 (syncing && locked == 0 && !test_bit(STRIPE_INSYNC, &sh->state)) {
                int update_p = 0, update_q = 0;
                struct r5dev *dev;

                set_bit(STRIPE_HANDLE, &sh->state);

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

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

        if (syncing && 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 (failed <= 2 && ! conf->mddev->ro)
                for (i=0; i<failed;i++) {
                        dev = &sh->dev[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);
                                }
                        }
                }
        spin_unlock(&sh->lock);

        while ((bi=return_bi)) {
                int bytes = bi->bi_size;

                return_bi = bi->bi_next;
                bi->bi_next = NULL;
                bi->bi_size = 0;
                bi->bi_end_io(bi, bytes, 0);
        }
        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 = 1;
                else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
                        rw = 0;
                else
                        continue;

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

                bi->bi_rw = rw;
                if (rw)
                        bi->bi_end_io = raid6_end_write_request;
                else
                        bi->bi_end_io = raid6_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 (syncing)
                                md_sync_acct(rdev->bdev, STRIPE_SECTORS);

                        bi->bi_bdev = rdev->bdev;
                        PRINTK("for %llu schedule op %ld on disc %d\n",
                                (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 == 1)
                                set_bit(STRIPE_DEGRADED, &sh->state);
                        PRINTK("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 inline void raid6_activate_delayed(raid6_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->handle_list);
                }
        }
}

static inline void activate_bit_delay(raid6_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)
{
        raid6_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)) {
                        request_queue_t *r_queue = bdev_get_queue(rdev->bdev);

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

                        if (r_queue->unplug_fn)
                                r_queue->unplug_fn(r_queue);

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

static void raid6_unplug_device(request_queue_t *q)
{
        mddev_t *mddev = q->queuedata;
        raid6_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++;
                raid6_activate_delayed(conf);
        }
        md_wakeup_thread(mddev->thread);

        spin_unlock_irqrestore(&conf->device_lock, flags);

        unplug_slaves(mddev);
}

static int raid6_issue_flush(request_queue_t *q, struct gendisk *disk,
                             sector_t *error_sector)
{
        mddev_t *mddev = q->queuedata;
        raid6_conf_t *conf = mddev_to_conf(mddev);
        int i, ret = 0;

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

                        if (!r_queue->issue_flush_fn)
                                ret = -EOPNOTSUPP;
                        else {
                                atomic_inc(&rdev->nr_pending);
                                rcu_read_unlock();
                                ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk,
                                                              error_sector);
                                rdev_dec_pending(rdev, mddev);
                                rcu_read_lock();
                        }
                }
        }
        rcu_read_unlock();
        return ret;
}

static inline void raid6_plug_device(raid6_conf_t *conf)
{
        spin_lock_irq(&conf->device_lock);
        blk_plug_device(conf->mddev->queue);
        spin_unlock_irq(&conf->device_lock);
}

static int make_request (request_queue_t *q, struct bio * bi)
{
        mddev_t *mddev = q->queuedata;
        raid6_conf_t *conf = mddev_to_conf(mddev);
        const unsigned int raid_disks = conf->raid_disks;
        const unsigned int data_disks = raid_disks - 2;
        unsigned int dd_idx, pd_idx;
        sector_t new_sector;
        sector_t logical_sector, last_sector;
        struct stripe_head *sh;
        const int rw = bio_data_dir(bi);

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

        md_write_start(mddev, bi);

        disk_stat_inc(mddev->gendisk, ios[rw]);
        disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bi));

        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);

                new_sector = raid6_compute_sector(logical_sector,
                                                  raid_disks, data_disks, &dd_idx, &pd_idx, conf);

                PRINTK("raid6: make_request, sector %llu logical %llu\n",
                       (unsigned long long)new_sector,
                       (unsigned long long)logical_sector);

        retry:
                prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
                sh = get_active_stripe(conf, new_sector, pd_idx, (bi->bi_rw&RWA_MASK));
                if (sh) {
                        if (!add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
                                /* Add failed due to overlap.  Flush everything
                                 * and wait a while
                                 */
                                raid6_unplug_device(mddev->queue);
                                release_stripe(sh);
                                schedule();
                                goto retry;
                        }
                        finish_wait(&conf->wait_for_overlap, &w);
                        raid6_plug_device(conf);
                        handle_stripe(sh, NULL);
                        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);
        if (--bi->bi_phys_segments == 0) {
                int bytes = bi->bi_size;

                if (rw == WRITE )
                        md_write_end(mddev);
                bi->bi_size = 0;
                bi->bi_end_io(bi, bytes, 0);
        }
        spin_unlock_irq(&conf->device_lock);
        return 0;
}

/* FIXME go_faster isn't used */
static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, int go_faster)
{
        raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
        struct stripe_head *sh;
        int sectors_per_chunk = conf->chunk_size >> 9;
        sector_t x;
        unsigned long stripe;
        int chunk_offset;
        int dd_idx, pd_idx;
        sector_t first_sector;
        int raid_disks = conf->raid_disks;
        int data_disks = raid_disks - 2;
        sector_t max_sector = mddev->size << 1;
        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 (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 there are 2 or more failed drives and we are trying
         * to resync, then assert that we are finished, because there is
         * nothing we can do.
         */
        if (mddev->degraded >= 2 && test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
                sector_t rv = (mddev->size << 1) - 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 */
        }

        x = sector_nr;
        chunk_offset = sector_div(x, sectors_per_chunk);
        stripe = x;
        BUG_ON(x != stripe);

        first_sector = raid6_compute_sector((sector_t)stripe*data_disks*sectors_per_chunk
                + chunk_offset, raid_disks, data_disks, &dd_idx, &pd_idx, conf);
        sh = get_active_stripe(conf, sector_nr, pd_idx, 1);
        if (sh == NULL) {
                sh = get_active_stripe(conf, sector_nr, pd_idx, 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);

        handle_stripe(sh, NULL);
        release_stripe(sh);

        return STRIPE_SECTORS;
}

/*
 * This is our raid6 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 raid6d (mddev_t *mddev)
{
        struct stripe_head *sh;
        raid6_conf_t *conf = mddev_to_conf(mddev);
        int handled;

        PRINTK("+++ raid6d active\n");

        md_check_recovery(mddev);

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

                if (conf->seq_flush - conf->seq_write > 0) {
                        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);
                }

                if (list_empty(&conf->handle_list) &&
                    atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD &&
                    !blk_queue_plugged(mddev->queue) &&
                    !list_empty(&conf->delayed_list))
                        raid6_activate_delayed(conf);

                if (list_empty(&conf->handle_list))
                        break;

                first = conf->handle_list.next;
                sh = list_entry(first, struct stripe_head, lru);

                list_del_init(first);
                atomic_inc(&sh->count);
                if (atomic_read(&sh->count)!= 1)
                        BUG();
                spin_unlock_irq(&conf->device_lock);

                handled++;
                handle_stripe(sh, conf->spare_page);
                release_stripe(sh);

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

        spin_unlock_irq(&conf->device_lock);

        unplug_slaves(mddev);

        PRINTK("--- raid6d inactive\n");
}

static int run(mddev_t *mddev)
{
        raid6_conf_t *conf;
        int raid_disk, memory;
        mdk_rdev_t *rdev;
        struct disk_info *disk;
        struct list_head *tmp;

        if (mddev->level != 6) {
                PRINTK("raid6: %s: raid level not set to 6 (%d)\n", mdname(mddev), mddev->level);
                return -EIO;
        }

        mddev->private = kzalloc(sizeof (raid6_conf_t)
                                 + mddev->raid_disks * sizeof(struct disk_info),
                                 GFP_KERNEL);
        if ((conf = mddev->private) == NULL)
                goto abort;
        conf->mddev = mddev;

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

        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->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);

        PRINTK("raid6: run(%s) called.\n", mdname(mddev));

        ITERATE_RDEV(mddev,rdev,tmp) {
                raid_disk = rdev->raid_disk;
                if (raid_disk >= mddev->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 "raid6: device %s operational as raid"
                               " disk %d\n", bdevname(rdev->bdev,b),
                               raid_disk);
                        conf->working_disks++;
                }
        }

        conf->raid_disks = mddev->raid_disks;

        /*
         * 0 for a fully functional array, 1 or 2 for a degraded array.
         */
        mddev->degraded = conf->failed_disks = conf->raid_disks - conf->working_disks;
        conf->mddev = mddev;
        conf->chunk_size = mddev->chunk_size;
        conf->level = mddev->level;
        conf->algorithm = mddev->layout;
        conf->max_nr_stripes = NR_STRIPES;

        /* device size must be a multiple of chunk size */
        mddev->size &= ~(mddev->chunk_size/1024 -1);
        mddev->resync_max_sectors = mddev->size << 1;

        if (conf->raid_disks < 4) {
                printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
                       mdname(mddev), conf->raid_disks);
                goto abort;
        }
        if (!conf->chunk_size || conf->chunk_size % 4) {
                printk(KERN_ERR "raid6: invalid chunk size %d for %s\n",
                       conf->chunk_size, mdname(mddev));
                goto abort;
        }
        if (conf->algorithm > ALGORITHM_RIGHT_SYMMETRIC) {
                printk(KERN_ERR
                       "raid6: unsupported parity algorithm %d for %s\n",
                       conf->algorithm, mdname(mddev));
                goto abort;
        }
        if (mddev->degraded > 2) {
                printk(KERN_ERR "raid6: not enough operational devices for %s"
                       " (%d/%d failed)\n",
                       mdname(mddev), conf->failed_disks, conf->raid_disks);
                goto abort;
        }

        if (mddev->degraded > 0 &&
            mddev->recovery_cp != MaxSector) {
                if (mddev->ok_start_degraded)
                        printk(KERN_WARNING "raid6: starting dirty degraded array:%s"
                               "- data corruption possible.\n",
                               mdname(mddev));
                else {
                        printk(KERN_ERR "raid6: cannot start dirty degraded array"
                               " for %s\n", mdname(mddev));
                        goto abort;
                }
        }

        {
                mddev->thread = md_register_thread(raid6d, mddev, "%s_raid6");
                if (!mddev->thread) {
                        printk(KERN_ERR
                               "raid6: couldn't allocate thread for %s\n",
                               mdname(mddev));
                        goto abort;
                }
        }

        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
                       "raid6: couldn't allocate %dkB for buffers\n", memory);
                shrink_stripes(conf);
                md_unregister_thread(mddev->thread);
                goto abort;
        } else
                printk(KERN_INFO "raid6: allocated %dkB for %s\n",
                       memory, mdname(mddev));

        if (mddev->degraded == 0)
                printk(KERN_INFO "raid6: 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,
                       conf->algorithm);
        else
                printk(KERN_ALERT "raid6: 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, conf->algorithm);

        print_raid6_conf(conf);

        /* read-ahead size must cover two whole stripes, which is
         * 2 * (n-2) * chunksize where 'n' is the number of raid devices
         */
        {
                int stripe = (mddev->raid_disks-2) * 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 */
        mddev->array_size =  mddev->size * (mddev->raid_disks - 2);

        mddev->queue->unplug_fn = raid6_unplug_device;
        mddev->queue->issue_flush_fn = raid6_issue_flush;
        return 0;
abort:
        if (conf) {
                print_raid6_conf(conf);
                safe_put_page(conf->spare_page);
                kfree(conf->stripe_hashtbl);
                kfree(conf);
        }
        mddev->private = NULL;
        printk(KERN_ALERT "raid6: failed to run raid set %s\n", mdname(mddev));
        return -EIO;
}



static int stop (mddev_t *mddev)
{
        raid6_conf_t *conf = (raid6_conf_t *) mddev->private;

        md_unregister_thread(mddev->thread);
        mddev->thread = NULL;
        shrink_stripes(conf);
        kfree(conf->stripe_hashtbl);
        blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
        kfree(conf);
        mddev->private = NULL;
        return 0;
}

#if RAID6_DUMPSTATE
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->raid_conf->raid_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, raid6_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++) {
                sh = conf->stripe_hashtbl[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)
{
        raid6_conf_t *conf = (raid6_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->working_disks);
        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, "]");
#if RAID6_DUMPSTATE
        seq_printf (seq, "\n");
        printall(seq, conf);
#endif
}

static void print_raid6_conf (raid6_conf_t *conf)
{
        int i;
        struct disk_info *tmp;

        printk("RAID6 conf printout:\n");
        if (!conf) {
                printk("(conf==NULL)\n");
                return;
        }
        printk(" --- rd:%d wd:%d fd:%d\n", conf->raid_disks,
                 conf->working_disks, conf->failed_disks);

        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 raid6_spare_active(mddev_t *mddev)
{
        int i;
        raid6_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_bit(In_sync, &tmp->rdev->flags)) {
                        mddev->degraded--;
                        conf->failed_disks--;
                        conf->working_disks++;
                        set_bit(In_sync, &tmp->rdev->flags);
                }
        }
        print_raid6_conf(conf);
        return 0;
}

static int raid6_remove_disk(mddev_t *mddev, int number)
{
        raid6_conf_t *conf = mddev->private;
        int err = 0;
        mdk_rdev_t *rdev;
        struct disk_info *p = conf->disks + number;

        print_raid6_conf(conf);
        rdev = p->rdev;
        if (rdev) {
                if (test_bit(In_sync, &rdev->flags) ||
                    atomic_read(&rdev->nr_pending)) {
                        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_raid6_conf(conf);
        return err;
}

static int raid6_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
{
        raid6_conf_t *conf = mddev->private;
        int found = 0;
        int disk;
        struct disk_info *p;

        if (mddev->degraded > 2)
                /* no point adding a device */
                return 0;
        /*
         * find the disk ... but prefer rdev->saved_raid_disk
         * if possible.
         */
        if (rdev->saved_raid_disk >= 0 &&
            conf->disks[rdev->saved_raid_disk].rdev == NULL)
                disk = rdev->saved_raid_disk;
        else
                disk = 0;
        for ( ; disk < mddev->raid_disks; disk++)
                if ((p=conf->disks + disk)->rdev == NULL) {
                        clear_bit(In_sync, &rdev->flags);
                        rdev->raid_disk = disk;
                        found = 1;
                        if (rdev->saved_raid_disk != disk)
                                conf->fullsync = 1;
                        rcu_assign_pointer(p->rdev, rdev);
                        break;
                }
        print_raid6_conf(conf);
        return found;
}

static int raid6_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);
        mddev->array_size = (sectors * (mddev->raid_disks-2))>>1;
        set_capacity(mddev->gendisk, mddev->array_size << 1);
        mddev->changed = 1;
        if (sectors/2  > mddev->size && mddev->recovery_cp == MaxSector) {
                mddev->recovery_cp = mddev->size << 1;
                set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
        }
        mddev->size = sectors /2;
        mddev->resync_max_sectors = sectors;
        return 0;
}

static void raid6_quiesce(mddev_t *mddev, int state)
{
        raid6_conf_t *conf = mddev_to_conf(mddev);

        switch(state) {
        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,
                                    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);
                spin_unlock_irq(&conf->device_lock);
                break;
        }
}

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   = raid6_add_disk,
        .hot_remove_disk= raid6_remove_disk,
        .spare_active   = raid6_spare_active,
        .sync_request   = sync_request,
        .resize         = raid6_resize,
        .quiesce        = raid6_quiesce,
};

static int __init raid6_init(void)
{
        int e;

        e = raid6_select_algo();
        if ( e )
                return e;

        return register_md_personality(&raid6_personality);
}

static void raid6_exit (void)
{
        unregister_md_personality(&raid6_personality);
}

module_init(raid6_init);
module_exit(raid6_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS("md-personality-8"); /* RAID6 */
MODULE_ALIAS("md-raid6");
MODULE_ALIAS("md-level-6");