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[safe/jmp/linux-2.6] / drivers / md / raid10.c

/*
 * raid10.c : Multiple Devices driver for Linux
 *
 * Copyright (C) 2000-2004 Neil Brown
 *
 * RAID-10 support for md.
 *
 * Base on code in raid1.c.  See raid1.c for futher copyright information.
 *
 *
 * 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 "dm-bio-list.h"
#include <linux/raid/raid10.h>
#include <linux/raid/bitmap.h>

/*
 * RAID10 provides a combination of RAID0 and RAID1 functionality.
 * The layout of data is defined by
 *    chunk_size
 *    raid_disks
 *    near_copies (stored in low byte of layout)
 *    far_copies (stored in second byte of layout)
 *    far_offset (stored in bit 16 of layout )
 *
 * The data to be stored is divided into chunks using chunksize.
 * Each device is divided into far_copies sections.
 * In each section, chunks are laid out in a style similar to raid0, but
 * near_copies copies of each chunk is stored (each on a different drive).
 * The starting device for each section is offset near_copies from the starting
 * device of the previous section.
 * Thus they are (near_copies*far_copies) of each chunk, and each is on a different
 * drive.
 * near_copies and far_copies must be at least one, and their product is at most
 * raid_disks.
 *
 * If far_offset is true, then the far_copies are handled a bit differently.
 * The copies are still in different stripes, but instead of be very far apart
 * on disk, there are adjacent stripes.
 */

/*
 * Number of guaranteed r10bios in case of extreme VM load:
 */
#define NR_RAID10_BIOS 256

static void unplug_slaves(mddev_t *mddev);

static void allow_barrier(conf_t *conf);
static void lower_barrier(conf_t *conf);

static void * r10bio_pool_alloc(gfp_t gfp_flags, void *data)
{
        conf_t *conf = data;
        r10bio_t *r10_bio;
        int size = offsetof(struct r10bio_s, devs[conf->copies]);

        /* allocate a r10bio with room for raid_disks entries in the bios array */
        r10_bio = kzalloc(size, gfp_flags);
        if (!r10_bio)
                unplug_slaves(conf->mddev);

        return r10_bio;
}

static void r10bio_pool_free(void *r10_bio, void *data)
{
        kfree(r10_bio);
}

#define RESYNC_BLOCK_SIZE (64*1024)
//#define RESYNC_BLOCK_SIZE PAGE_SIZE
#define RESYNC_SECTORS (RESYNC_BLOCK_SIZE >> 9)
#define RESYNC_PAGES ((RESYNC_BLOCK_SIZE + PAGE_SIZE-1) / PAGE_SIZE)
#define RESYNC_WINDOW (2048*1024)

/*
 * When performing a resync, we need to read and compare, so
 * we need as many pages are there are copies.
 * When performing a recovery, we need 2 bios, one for read,
 * one for write (we recover only one drive per r10buf)
 *
 */
static void * r10buf_pool_alloc(gfp_t gfp_flags, void *data)
{
        conf_t *conf = data;
        struct page *page;
        r10bio_t *r10_bio;
        struct bio *bio;
        int i, j;
        int nalloc;

        r10_bio = r10bio_pool_alloc(gfp_flags, conf);
        if (!r10_bio) {
                unplug_slaves(conf->mddev);
                return NULL;
        }

        if (test_bit(MD_RECOVERY_SYNC, &conf->mddev->recovery))
                nalloc = conf->copies; /* resync */
        else
                nalloc = 2; /* recovery */

        /*
         * Allocate bios.
         */
        for (j = nalloc ; j-- ; ) {
                bio = bio_alloc(gfp_flags, RESYNC_PAGES);
                if (!bio)
                        goto out_free_bio;
                r10_bio->devs[j].bio = bio;
        }
        /*
         * Allocate RESYNC_PAGES data pages and attach them
         * where needed.
         */
        for (j = 0 ; j < nalloc; j++) {
                bio = r10_bio->devs[j].bio;
                for (i = 0; i < RESYNC_PAGES; i++) {
                        page = alloc_page(gfp_flags);
                        if (unlikely(!page))
                                goto out_free_pages;

                        bio->bi_io_vec[i].bv_page = page;
                }
        }

        return r10_bio;

out_free_pages:
        for ( ; i > 0 ; i--)
                safe_put_page(bio->bi_io_vec[i-1].bv_page);
        while (j--)
                for (i = 0; i < RESYNC_PAGES ; i++)
                        safe_put_page(r10_bio->devs[j].bio->bi_io_vec[i].bv_page);
        j = -1;
out_free_bio:
        while ( ++j < nalloc )
                bio_put(r10_bio->devs[j].bio);
        r10bio_pool_free(r10_bio, conf);
        return NULL;
}

static void r10buf_pool_free(void *__r10_bio, void *data)
{
        int i;
        conf_t *conf = data;
        r10bio_t *r10bio = __r10_bio;
        int j;

        for (j=0; j < conf->copies; j++) {
                struct bio *bio = r10bio->devs[j].bio;
                if (bio) {
                        for (i = 0; i < RESYNC_PAGES; i++) {
                                safe_put_page(bio->bi_io_vec[i].bv_page);
                                bio->bi_io_vec[i].bv_page = NULL;
                        }
                        bio_put(bio);
                }
        }
        r10bio_pool_free(r10bio, conf);
}

static void put_all_bios(conf_t *conf, r10bio_t *r10_bio)
{
        int i;

        for (i = 0; i < conf->copies; i++) {
                struct bio **bio = & r10_bio->devs[i].bio;
                if (*bio && *bio != IO_BLOCKED)
                        bio_put(*bio);
                *bio = NULL;
        }
}

static void free_r10bio(r10bio_t *r10_bio)
{
        conf_t *conf = mddev_to_conf(r10_bio->mddev);

        /*
         * Wake up any possible resync thread that waits for the device
         * to go idle.
         */
        allow_barrier(conf);

        put_all_bios(conf, r10_bio);
        mempool_free(r10_bio, conf->r10bio_pool);
}

static void put_buf(r10bio_t *r10_bio)
{
        conf_t *conf = mddev_to_conf(r10_bio->mddev);

        mempool_free(r10_bio, conf->r10buf_pool);

        lower_barrier(conf);
}

static void reschedule_retry(r10bio_t *r10_bio)
{
        unsigned long flags;
        mddev_t *mddev = r10_bio->mddev;
        conf_t *conf = mddev_to_conf(mddev);

        spin_lock_irqsave(&conf->device_lock, flags);
        list_add(&r10_bio->retry_list, &conf->retry_list);
        conf->nr_queued ++;
        spin_unlock_irqrestore(&conf->device_lock, flags);

        md_wakeup_thread(mddev->thread);
}

/*
 * raid_end_bio_io() is called when we have finished servicing a mirrored
 * operation and are ready to return a success/failure code to the buffer
 * cache layer.
 */
static void raid_end_bio_io(r10bio_t *r10_bio)
{
        struct bio *bio = r10_bio->master_bio;

        bio_endio(bio,
                test_bit(R10BIO_Uptodate, &r10_bio->state) ? 0 : -EIO);
        free_r10bio(r10_bio);
}

/*
 * Update disk head position estimator based on IRQ completion info.
 */
static inline void update_head_pos(int slot, r10bio_t *r10_bio)
{
        conf_t *conf = mddev_to_conf(r10_bio->mddev);

        conf->mirrors[r10_bio->devs[slot].devnum].head_position =
                r10_bio->devs[slot].addr + (r10_bio->sectors);
}

static void raid10_end_read_request(struct bio *bio, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        r10bio_t * r10_bio = (r10bio_t *)(bio->bi_private);
        int slot, dev;
        conf_t *conf = mddev_to_conf(r10_bio->mddev);


        slot = r10_bio->read_slot;
        dev = r10_bio->devs[slot].devnum;
        /*
         * this branch is our 'one mirror IO has finished' event handler:
         */
        update_head_pos(slot, r10_bio);

        if (uptodate) {
                /*
                 * Set R10BIO_Uptodate in our master bio, so that
                 * we will return a good error code to the higher
                 * levels even if IO on some other mirrored buffer fails.
                 *
                 * The 'master' represents the composite IO operation to
                 * user-side. So if something waits for IO, then it will
                 * wait for the 'master' bio.
                 */
                set_bit(R10BIO_Uptodate, &r10_bio->state);
                raid_end_bio_io(r10_bio);
        } else {
                /*
                 * oops, read error:
                 */
                char b[BDEVNAME_SIZE];
                if (printk_ratelimit())
                        printk(KERN_ERR "raid10: %s: rescheduling sector %llu\n",
                               bdevname(conf->mirrors[dev].rdev->bdev,b), (unsigned long long)r10_bio->sector);
                reschedule_retry(r10_bio);
        }

        rdev_dec_pending(conf->mirrors[dev].rdev, conf->mddev);
}

static void raid10_end_write_request(struct bio *bio, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        r10bio_t * r10_bio = (r10bio_t *)(bio->bi_private);
        int slot, dev;
        conf_t *conf = mddev_to_conf(r10_bio->mddev);

        for (slot = 0; slot < conf->copies; slot++)
                if (r10_bio->devs[slot].bio == bio)
                        break;
        dev = r10_bio->devs[slot].devnum;

        /*
         * this branch is our 'one mirror IO has finished' event handler:
         */
        if (!uptodate) {
                md_error(r10_bio->mddev, conf->mirrors[dev].rdev);
                /* an I/O failed, we can't clear the bitmap */
                set_bit(R10BIO_Degraded, &r10_bio->state);
        } else
                /*
                 * Set R10BIO_Uptodate in our master bio, so that
                 * we will return a good error code for to the higher
                 * levels even if IO on some other mirrored buffer fails.
                 *
                 * The 'master' represents the composite IO operation to
                 * user-side. So if something waits for IO, then it will
                 * wait for the 'master' bio.
                 */
                set_bit(R10BIO_Uptodate, &r10_bio->state);

        update_head_pos(slot, r10_bio);

        /*
         *
         * Let's see if all mirrored write operations have finished
         * already.
         */
        if (atomic_dec_and_test(&r10_bio->remaining)) {
                /* clear the bitmap if all writes complete successfully */
                bitmap_endwrite(r10_bio->mddev->bitmap, r10_bio->sector,
                                r10_bio->sectors,
                                !test_bit(R10BIO_Degraded, &r10_bio->state),
                                0);
                md_write_end(r10_bio->mddev);
                raid_end_bio_io(r10_bio);
        }

        rdev_dec_pending(conf->mirrors[dev].rdev, conf->mddev);
}


/*
 * RAID10 layout manager
 * Aswell as the chunksize and raid_disks count, there are two
 * parameters: near_copies and far_copies.
 * near_copies * far_copies must be <= raid_disks.
 * Normally one of these will be 1.
 * If both are 1, we get raid0.
 * If near_copies == raid_disks, we get raid1.
 *
 * Chunks are layed out in raid0 style with near_copies copies of the
 * first chunk, followed by near_copies copies of the next chunk and
 * so on.
 * If far_copies > 1, then after 1/far_copies of the array has been assigned
 * as described above, we start again with a device offset of near_copies.
 * So we effectively have another copy of the whole array further down all
 * the drives, but with blocks on different drives.
 * With this layout, and block is never stored twice on the one device.
 *
 * raid10_find_phys finds the sector offset of a given virtual sector
 * on each device that it is on.
 *
 * raid10_find_virt does the reverse mapping, from a device and a
 * sector offset to a virtual address
 */

static void raid10_find_phys(conf_t *conf, r10bio_t *r10bio)
{
        int n,f;
        sector_t sector;
        sector_t chunk;
        sector_t stripe;
        int dev;

        int slot = 0;

        /* now calculate first sector/dev */
        chunk = r10bio->sector >> conf->chunk_shift;
        sector = r10bio->sector & conf->chunk_mask;

        chunk *= conf->near_copies;
        stripe = chunk;
        dev = sector_div(stripe, conf->raid_disks);
        if (conf->far_offset)
                stripe *= conf->far_copies;

        sector += stripe << conf->chunk_shift;

        /* and calculate all the others */
        for (n=0; n < conf->near_copies; n++) {
                int d = dev;
                sector_t s = sector;
                r10bio->devs[slot].addr = sector;
                r10bio->devs[slot].devnum = d;
                slot++;

                for (f = 1; f < conf->far_copies; f++) {
                        d += conf->near_copies;
                        if (d >= conf->raid_disks)
                                d -= conf->raid_disks;
                        s += conf->stride;
                        r10bio->devs[slot].devnum = d;
                        r10bio->devs[slot].addr = s;
                        slot++;
                }
                dev++;
                if (dev >= conf->raid_disks) {
                        dev = 0;
                        sector += (conf->chunk_mask + 1);
                }
        }
        BUG_ON(slot != conf->copies);
}

static sector_t raid10_find_virt(conf_t *conf, sector_t sector, int dev)
{
        sector_t offset, chunk, vchunk;

        offset = sector & conf->chunk_mask;
        if (conf->far_offset) {
                int fc;
                chunk = sector >> conf->chunk_shift;
                fc = sector_div(chunk, conf->far_copies);
                dev -= fc * conf->near_copies;
                if (dev < 0)
                        dev += conf->raid_disks;
        } else {
                while (sector >= conf->stride) {
                        sector -= conf->stride;
                        if (dev < conf->near_copies)
                                dev += conf->raid_disks - conf->near_copies;
                        else
                                dev -= conf->near_copies;
                }
                chunk = sector >> conf->chunk_shift;
        }
        vchunk = chunk * conf->raid_disks + dev;
        sector_div(vchunk, conf->near_copies);
        return (vchunk << conf->chunk_shift) + offset;
}

/**
 *      raid10_mergeable_bvec -- tell bio layer if a two requests can be merged
 *      @q: request queue
 *      @bio: the buffer head that's been built up so far
 *      @biovec: the request that could be merged to it.
 *
 *      Return amount of bytes we can accept at this offset
 *      If near_copies == raid_disk, there are no striping issues,
 *      but in that case, the function isn't called at all.
 */
static int raid10_mergeable_bvec(struct request_queue *q, struct bio *bio,
                                struct bio_vec *bio_vec)
{
        mddev_t *mddev = q->queuedata;
        sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);
        int max;
        unsigned int chunk_sectors = mddev->chunk_size >> 9;
        unsigned int bio_sectors = bio->bi_size >> 9;

        max =  (chunk_sectors - ((sector & (chunk_sectors - 1)) + bio_sectors)) << 9;
        if (max < 0) max = 0; /* bio_add cannot handle a negative return */
        if (max <= bio_vec->bv_len && bio_sectors == 0)
                return bio_vec->bv_len;
        else
                return max;
}

/*
 * This routine returns the disk from which the requested read should
 * be done. There is a per-array 'next expected sequential IO' sector
 * number - if this matches on the next IO then we use the last disk.
 * There is also a per-disk 'last know head position' sector that is
 * maintained from IRQ contexts, both the normal and the resync IO
 * completion handlers update this position correctly. If there is no
 * perfect sequential match then we pick the disk whose head is closest.
 *
 * If there are 2 mirrors in the same 2 devices, performance degrades
 * because position is mirror, not device based.
 *
 * The rdev for the device selected will have nr_pending incremented.
 */

/*
 * FIXME: possibly should rethink readbalancing and do it differently
 * depending on near_copies / far_copies geometry.
 */
static int read_balance(conf_t *conf, r10bio_t *r10_bio)
{
        const unsigned long this_sector = r10_bio->sector;
        int disk, slot, nslot;
        const int sectors = r10_bio->sectors;
        sector_t new_distance, current_distance;
        mdk_rdev_t *rdev;

        raid10_find_phys(conf, r10_bio);
        rcu_read_lock();
        /*
         * Check if we can balance. We can balance on the whole
         * device if no resync is going on (recovery is ok), or below
         * the resync window. We take the first readable disk when
         * above the resync window.
         */
        if (conf->mddev->recovery_cp < MaxSector
            && (this_sector + sectors >= conf->next_resync)) {
                /* make sure that disk is operational */
                slot = 0;
                disk = r10_bio->devs[slot].devnum;

                while ((rdev = rcu_dereference(conf->mirrors[disk].rdev)) == NULL ||
                       r10_bio->devs[slot].bio == IO_BLOCKED ||
                       !test_bit(In_sync, &rdev->flags)) {
                        slot++;
                        if (slot == conf->copies) {
                                slot = 0;
                                disk = -1;
                                break;
                        }
                        disk = r10_bio->devs[slot].devnum;
                }
                goto rb_out;
        }


        /* make sure the disk is operational */
        slot = 0;
        disk = r10_bio->devs[slot].devnum;
        while ((rdev=rcu_dereference(conf->mirrors[disk].rdev)) == NULL ||
               r10_bio->devs[slot].bio == IO_BLOCKED ||
               !test_bit(In_sync, &rdev->flags)) {
                slot ++;
                if (slot == conf->copies) {
                        disk = -1;
                        goto rb_out;
                }
                disk = r10_bio->devs[slot].devnum;
        }


        current_distance = abs(r10_bio->devs[slot].addr -
                               conf->mirrors[disk].head_position);

        /* Find the disk whose head is closest */

        for (nslot = slot; nslot < conf->copies; nslot++) {
                int ndisk = r10_bio->devs[nslot].devnum;


                if ((rdev=rcu_dereference(conf->mirrors[ndisk].rdev)) == NULL ||
                    r10_bio->devs[nslot].bio == IO_BLOCKED ||
                    !test_bit(In_sync, &rdev->flags))
                        continue;

                /* This optimisation is debatable, and completely destroys
                 * sequential read speed for 'far copies' arrays.  So only
                 * keep it for 'near' arrays, and review those later.
                 */
                if (conf->near_copies > 1 && !atomic_read(&rdev->nr_pending)) {
                        disk = ndisk;
                        slot = nslot;
                        break;
                }
                new_distance = abs(r10_bio->devs[nslot].addr -
                                   conf->mirrors[ndisk].head_position);
                if (new_distance < current_distance) {
                        current_distance = new_distance;
                        disk = ndisk;
                        slot = nslot;
                }
        }

rb_out:
        r10_bio->read_slot = slot;
/*      conf->next_seq_sect = this_sector + sectors;*/

        if (disk >= 0 && (rdev=rcu_dereference(conf->mirrors[disk].rdev))!= NULL)
                atomic_inc(&conf->mirrors[disk].rdev->nr_pending);
        else
                disk = -1;
        rcu_read_unlock();

        return disk;
}

static void unplug_slaves(mddev_t *mddev)
{
        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->mirrors[i].rdev);
                if (rdev && !test_bit(Faulty, &rdev->flags) && atomic_read(&rdev->nr_pending)) {
                        struct request_queue *r_queue = bdev_get_queue(rdev->bdev);

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

                        blk_unplug(r_queue);

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

static void raid10_unplug(struct request_queue *q)
{
        mddev_t *mddev = q->queuedata;

        unplug_slaves(q->queuedata);
        md_wakeup_thread(mddev->thread);
}

static int raid10_congested(void *data, int bits)
{
        mddev_t *mddev = data;
        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->mirrors[i].rdev);
                if (rdev && !test_bit(Faulty, &rdev->flags)) {
                        struct request_queue *q = bdev_get_queue(rdev->bdev);

                        ret |= bdi_congested(&q->backing_dev_info, bits);
                }
        }
        rcu_read_unlock();
        return ret;
}


/* Barriers....
 * Sometimes we need to suspend IO while we do something else,
 * either some resync/recovery, or reconfigure the array.
 * To do this we raise a 'barrier'.
 * The 'barrier' is a counter that can be raised multiple times
 * to count how many activities are happening which preclude
 * normal IO.
 * We can only raise the barrier if there is no pending IO.
 * i.e. if nr_pending == 0.
 * We choose only to raise the barrier if no-one is waiting for the
 * barrier to go down.  This means that as soon as an IO request
 * is ready, no other operations which require a barrier will start
 * until the IO request has had a chance.
 *
 * So: regular IO calls 'wait_barrier'.  When that returns there
 *    is no backgroup IO happening,  It must arrange to call
 *    allow_barrier when it has finished its IO.
 * backgroup IO calls must call raise_barrier.  Once that returns
 *    there is no normal IO happeing.  It must arrange to call
 *    lower_barrier when the particular background IO completes.
 */
#define RESYNC_DEPTH 32

static void raise_barrier(conf_t *conf, int force)
{
        BUG_ON(force && !conf->barrier);
        spin_lock_irq(&conf->resync_lock);

        /* Wait until no block IO is waiting (unless 'force') */
        wait_event_lock_irq(conf->wait_barrier, force || !conf->nr_waiting,
                            conf->resync_lock,
                            raid10_unplug(conf->mddev->queue));

        /* block any new IO from starting */
        conf->barrier++;

        /* No wait for all pending IO to complete */
        wait_event_lock_irq(conf->wait_barrier,
                            !conf->nr_pending && conf->barrier < RESYNC_DEPTH,
                            conf->resync_lock,
                            raid10_unplug(conf->mddev->queue));

        spin_unlock_irq(&conf->resync_lock);
}

static void lower_barrier(conf_t *conf)
{
        unsigned long flags;
        spin_lock_irqsave(&conf->resync_lock, flags);
        conf->barrier--;
        spin_unlock_irqrestore(&conf->resync_lock, flags);
        wake_up(&conf->wait_barrier);
}

static void wait_barrier(conf_t *conf)
{
        spin_lock_irq(&conf->resync_lock);
        if (conf->barrier) {
                conf->nr_waiting++;
                wait_event_lock_irq(conf->wait_barrier, !conf->barrier,
                                    conf->resync_lock,
                                    raid10_unplug(conf->mddev->queue));
                conf->nr_waiting--;
        }
        conf->nr_pending++;
        spin_unlock_irq(&conf->resync_lock);
}

static void allow_barrier(conf_t *conf)
{
        unsigned long flags;
        spin_lock_irqsave(&conf->resync_lock, flags);
        conf->nr_pending--;
        spin_unlock_irqrestore(&conf->resync_lock, flags);
        wake_up(&conf->wait_barrier);
}

static void freeze_array(conf_t *conf)
{
        /* stop syncio and normal IO and wait for everything to
         * go quiet.
         * We increment barrier and nr_waiting, and then
         * wait until barrier+nr_pending match nr_queued+2
         */
        spin_lock_irq(&conf->resync_lock);
        conf->barrier++;
        conf->nr_waiting++;
        wait_event_lock_irq(conf->wait_barrier,
                            conf->barrier+conf->nr_pending == conf->nr_queued+2,
                            conf->resync_lock,
                            raid10_unplug(conf->mddev->queue));
        spin_unlock_irq(&conf->resync_lock);
}

static void unfreeze_array(conf_t *conf)
{
        /* reverse the effect of the freeze */
        spin_lock_irq(&conf->resync_lock);
        conf->barrier--;
        conf->nr_waiting--;
        wake_up(&conf->wait_barrier);
        spin_unlock_irq(&conf->resync_lock);
}

static int make_request(struct request_queue *q, struct bio * bio)
{
        mddev_t *mddev = q->queuedata;
        conf_t *conf = mddev_to_conf(mddev);
        mirror_info_t *mirror;
        r10bio_t *r10_bio;
        struct bio *read_bio;
        int i;
        int chunk_sects = conf->chunk_mask + 1;
        const int rw = bio_data_dir(bio);
        const int do_sync = bio_sync(bio);
        struct bio_list bl;
        unsigned long flags;

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

        /* If this request crosses a chunk boundary, we need to
         * split it.  This will only happen for 1 PAGE (or less) requests.
         */
        if (unlikely( (bio->bi_sector & conf->chunk_mask) + (bio->bi_size >> 9)
                      > chunk_sects &&
                    conf->near_copies < conf->raid_disks)) {
                struct bio_pair *bp;
                /* Sanity check -- queue functions should prevent this happening */
                if (bio->bi_vcnt != 1 ||
                    bio->bi_idx != 0)
                        goto bad_map;
                /* This is a one page bio that upper layers
                 * refuse to split for us, so we need to split it.
                 */
                bp = bio_split(bio, bio_split_pool,
                               chunk_sects - (bio->bi_sector & (chunk_sects - 1)) );
                if (make_request(q, &bp->bio1))
                        generic_make_request(&bp->bio1);
                if (make_request(q, &bp->bio2))
                        generic_make_request(&bp->bio2);

                bio_pair_release(bp);
                return 0;
        bad_map:
                printk("raid10_make_request bug: can't convert block across chunks"
                       " or bigger than %dk %llu %d\n", chunk_sects/2,
                       (unsigned long long)bio->bi_sector, bio->bi_size >> 10);

                bio_io_error(bio);
                return 0;
        }

        md_write_start(mddev, bio);

        /*
         * Register the new request and wait if the reconstruction
         * thread has put up a bar for new requests.
         * Continue immediately if no resync is active currently.
         */
        wait_barrier(conf);

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

        r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);

        r10_bio->master_bio = bio;
        r10_bio->sectors = bio->bi_size >> 9;

        r10_bio->mddev = mddev;
        r10_bio->sector = bio->bi_sector;
        r10_bio->state = 0;

        if (rw == READ) {
                /*
                 * read balancing logic:
                 */
                int disk = read_balance(conf, r10_bio);
                int slot = r10_bio->read_slot;
                if (disk < 0) {
                        raid_end_bio_io(r10_bio);
                        return 0;
                }
                mirror = conf->mirrors + disk;

                read_bio = bio_clone(bio, GFP_NOIO);

                r10_bio->devs[slot].bio = read_bio;

                read_bio->bi_sector = r10_bio->devs[slot].addr +
                        mirror->rdev->data_offset;
                read_bio->bi_bdev = mirror->rdev->bdev;
                read_bio->bi_end_io = raid10_end_read_request;
                read_bio->bi_rw = READ | do_sync;
                read_bio->bi_private = r10_bio;

                generic_make_request(read_bio);
                return 0;
        }

        /*
         * WRITE:
         */
        /* first select target devices under spinlock and
         * inc refcount on their rdev.  Record them by setting
         * bios[x] to bio
         */
        raid10_find_phys(conf, r10_bio);
        rcu_read_lock();
        for (i = 0;  i < conf->copies; i++) {
                int d = r10_bio->devs[i].devnum;
                mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[d].rdev);
                if (rdev &&
                    !test_bit(Faulty, &rdev->flags)) {
                        atomic_inc(&rdev->nr_pending);
                        r10_bio->devs[i].bio = bio;
                } else {
                        r10_bio->devs[i].bio = NULL;
                        set_bit(R10BIO_Degraded, &r10_bio->state);
                }
        }
        rcu_read_unlock();

        atomic_set(&r10_bio->remaining, 0);

        bio_list_init(&bl);
        for (i = 0; i < conf->copies; i++) {
                struct bio *mbio;
                int d = r10_bio->devs[i].devnum;
                if (!r10_bio->devs[i].bio)
                        continue;

                mbio = bio_clone(bio, GFP_NOIO);
                r10_bio->devs[i].bio = mbio;

                mbio->bi_sector = r10_bio->devs[i].addr+
                        conf->mirrors[d].rdev->data_offset;
                mbio->bi_bdev = conf->mirrors[d].rdev->bdev;
                mbio->bi_end_io = raid10_end_write_request;
                mbio->bi_rw = WRITE | do_sync;
                mbio->bi_private = r10_bio;

                atomic_inc(&r10_bio->remaining);
                bio_list_add(&bl, mbio);
        }

        if (unlikely(!atomic_read(&r10_bio->remaining))) {
                /* the array is dead */
                md_write_end(mddev);
                raid_end_bio_io(r10_bio);
                return 0;
        }

        bitmap_startwrite(mddev->bitmap, bio->bi_sector, r10_bio->sectors, 0);
        spin_lock_irqsave(&conf->device_lock, flags);
        bio_list_merge(&conf->pending_bio_list, &bl);
        blk_plug_device(mddev->queue);
        spin_unlock_irqrestore(&conf->device_lock, flags);

        if (do_sync)
                md_wakeup_thread(mddev->thread);

        return 0;
}

static void status(struct seq_file *seq, mddev_t *mddev)
{
        conf_t *conf = mddev_to_conf(mddev);
        int i;

        if (conf->near_copies < conf->raid_disks)
                seq_printf(seq, " %dK chunks", mddev->chunk_size/1024);
        if (conf->near_copies > 1)
                seq_printf(seq, " %d near-copies", conf->near_copies);
        if (conf->far_copies > 1) {
                if (conf->far_offset)
                        seq_printf(seq, " %d offset-copies", conf->far_copies);
                else
                        seq_printf(seq, " %d far-copies", conf->far_copies);
        }
        seq_printf(seq, " [%d/%d] [", conf->raid_disks,
                                        conf->raid_disks - mddev->degraded);
        for (i = 0; i < conf->raid_disks; i++)
                seq_printf(seq, "%s",
                              conf->mirrors[i].rdev &&
                              test_bit(In_sync, &conf->mirrors[i].rdev->flags) ? "U" : "_");
        seq_printf(seq, "]");
}

static void error(mddev_t *mddev, mdk_rdev_t *rdev)
{
        char b[BDEVNAME_SIZE];
        conf_t *conf = mddev_to_conf(mddev);

        /*
         * If it is not operational, then we have already marked it as dead
         * else if it is the last working disks, ignore the error, let the
         * next level up know.
         * else mark the drive as failed
         */
        if (test_bit(In_sync, &rdev->flags)
            && conf->raid_disks-mddev->degraded == 1)
                /*
                 * Don't fail the drive, just return an IO error.
                 * The test should really be more sophisticated than
                 * "working_disks == 1", but it isn't critical, and
                 * can wait until we do more sophisticated "is the drive
                 * really dead" tests...
                 */
                return;
        if (test_and_clear_bit(In_sync, &rdev->flags)) {
                unsigned long flags;
                spin_lock_irqsave(&conf->device_lock, flags);
                mddev->degraded++;
                spin_unlock_irqrestore(&conf->device_lock, flags);
                /*
                 * if recovery is running, make sure it aborts.
                 */
                set_bit(MD_RECOVERY_ERR, &mddev->recovery);
        }
        set_bit(Faulty, &rdev->flags);
        set_bit(MD_CHANGE_DEVS, &mddev->flags);
        printk(KERN_ALERT "raid10: Disk failure on %s, disabling device. \n"
                "       Operation continuing on %d devices\n",
                bdevname(rdev->bdev,b), conf->raid_disks - mddev->degraded);
}

static void print_conf(conf_t *conf)
{
        int i;
        mirror_info_t *tmp;

        printk("RAID10 conf printout:\n");
        if (!conf) {
                printk("(!conf)\n");
                return;
        }
        printk(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
                conf->raid_disks);

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

static void close_sync(conf_t *conf)
{
        wait_barrier(conf);
        allow_barrier(conf);

        mempool_destroy(conf->r10buf_pool);
        conf->r10buf_pool = NULL;
}

/* check if there are enough drives for
 * every block to appear on atleast one
 */
static int enough(conf_t *conf)
{
        int first = 0;

        do {
                int n = conf->copies;
                int cnt = 0;
                while (n--) {
                        if (conf->mirrors[first].rdev)
                                cnt++;
                        first = (first+1) % conf->raid_disks;
                }
                if (cnt == 0)
                        return 0;
        } while (first != 0);
        return 1;
}

static int raid10_spare_active(mddev_t *mddev)
{
        int i;
        conf_t *conf = mddev->private;
        mirror_info_t *tmp;

        /*
         * Find all non-in_sync disks within the RAID10 configuration
         * and mark them in_sync
         */
        for (i = 0; i < conf->raid_disks; i++) {
                tmp = conf->mirrors + i;
                if (tmp->rdev
                    && !test_bit(Faulty, &tmp->rdev->flags)
                    && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
                        unsigned long flags;
                        spin_lock_irqsave(&conf->device_lock, flags);
                        mddev->degraded--;
                        spin_unlock_irqrestore(&conf->device_lock, flags);
                }
        }

        print_conf(conf);
        return 0;
}


static int raid10_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
{
        conf_t *conf = mddev->private;
        int found = 0;
        int mirror;
        mirror_info_t *p;

        if (mddev->recovery_cp < MaxSector)
                /* only hot-add to in-sync arrays, as recovery is
                 * very different from resync
                 */
                return 0;
        if (!enough(conf))
                return 0;

        if (rdev->saved_raid_disk >= 0 &&
            conf->mirrors[rdev->saved_raid_disk].rdev == NULL)
                mirror = rdev->saved_raid_disk;
        else
                mirror = 0;
        for ( ; mirror < mddev->raid_disks; mirror++)
                if ( !(p=conf->mirrors+mirror)->rdev) {

                        blk_queue_stack_limits(mddev->queue,
                                               rdev->bdev->bd_disk->queue);
                        /* as we don't honour merge_bvec_fn, we must never risk
                         * violating it, so limit ->max_sector to one PAGE, as
                         * a one page request is never in violation.
                         */
                        if (rdev->bdev->bd_disk->queue->merge_bvec_fn &&
                            mddev->queue->max_sectors > (PAGE_SIZE>>9))
                                mddev->queue->max_sectors = (PAGE_SIZE>>9);

                        p->head_position = 0;
                        rdev->raid_disk = mirror;
                        found = 1;
                        if (rdev->saved_raid_disk != mirror)
                                conf->fullsync = 1;
                        rcu_assign_pointer(p->rdev, rdev);
                        break;
                }

        print_conf(conf);
        return found;
}

static int raid10_remove_disk(mddev_t *mddev, int number)
{
        conf_t *conf = mddev->private;
        int err = 0;
        mdk_rdev_t *rdev;
        mirror_info_t *p = conf->mirrors+ number;

        print_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_conf(conf);
        return err;
}


static void end_sync_read(struct bio *bio, int error)
{
        r10bio_t * r10_bio = (r10bio_t *)(bio->bi_private);
        conf_t *conf = mddev_to_conf(r10_bio->mddev);
        int i,d;

        for (i=0; i<conf->copies; i++)
                if (r10_bio->devs[i].bio == bio)
                        break;
        BUG_ON(i == conf->copies);
        update_head_pos(i, r10_bio);
        d = r10_bio->devs[i].devnum;

        if (test_bit(BIO_UPTODATE, &bio->bi_flags))
                set_bit(R10BIO_Uptodate, &r10_bio->state);
        else {
                atomic_add(r10_bio->sectors,
                           &conf->mirrors[d].rdev->corrected_errors);
                if (!test_bit(MD_RECOVERY_SYNC, &conf->mddev->recovery))
                        md_error(r10_bio->mddev,
                                 conf->mirrors[d].rdev);
        }

        /* for reconstruct, we always reschedule after a read.
         * for resync, only after all reads
         */
        if (test_bit(R10BIO_IsRecover, &r10_bio->state) ||
            atomic_dec_and_test(&r10_bio->remaining)) {
                /* we have read all the blocks,
                 * do the comparison in process context in raid10d
                 */
                reschedule_retry(r10_bio);
        }
        rdev_dec_pending(conf->mirrors[d].rdev, conf->mddev);
}

static void end_sync_write(struct bio *bio, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        r10bio_t * r10_bio = (r10bio_t *)(bio->bi_private);
        mddev_t *mddev = r10_bio->mddev;
        conf_t *conf = mddev_to_conf(mddev);
        int i,d;

        for (i = 0; i < conf->copies; i++)
                if (r10_bio->devs[i].bio == bio)
                        break;
        d = r10_bio->devs[i].devnum;

        if (!uptodate)
                md_error(mddev, conf->mirrors[d].rdev);
        update_head_pos(i, r10_bio);

        while (atomic_dec_and_test(&r10_bio->remaining)) {
                if (r10_bio->master_bio == NULL) {
                        /* the primary of several recovery bios */
                        md_done_sync(mddev, r10_bio->sectors, 1);
                        put_buf(r10_bio);
                        break;
                } else {
                        r10bio_t *r10_bio2 = (r10bio_t *)r10_bio->master_bio;
                        put_buf(r10_bio);
                        r10_bio = r10_bio2;
                }
        }
        rdev_dec_pending(conf->mirrors[d].rdev, mddev);
}

/*
 * Note: sync and recover and handled very differently for raid10
 * This code is for resync.
 * For resync, we read through virtual addresses and read all blocks.
 * If there is any error, we schedule a write.  The lowest numbered
 * drive is authoritative.
 * However requests come for physical address, so we need to map.
 * For every physical address there are raid_disks/copies virtual addresses,
 * which is always are least one, but is not necessarly an integer.
 * This means that a physical address can span multiple chunks, so we may
 * have to submit multiple io requests for a single sync request.
 */
/*
 * We check if all blocks are in-sync and only write to blocks that
 * aren't in sync
 */
static void sync_request_write(mddev_t *mddev, r10bio_t *r10_bio)
{
        conf_t *conf = mddev_to_conf(mddev);
        int i, first;
        struct bio *tbio, *fbio;

        atomic_set(&r10_bio->remaining, 1);

        /* find the first device with a block */
        for (i=0; i<conf->copies; i++)
                if (test_bit(BIO_UPTODATE, &r10_bio->devs[i].bio->bi_flags))
                        break;

        if (i == conf->copies)
                goto done;

        first = i;
        fbio = r10_bio->devs[i].bio;

        /* now find blocks with errors */
        for (i=0 ; i < conf->copies ; i++) {
                int  j, d;
                int vcnt = r10_bio->sectors >> (PAGE_SHIFT-9);

                tbio = r10_bio->devs[i].bio;

                if (tbio->bi_end_io != end_sync_read)
                        continue;
                if (i == first)
                        continue;
                if (test_bit(BIO_UPTODATE, &r10_bio->devs[i].bio->bi_flags)) {
                        /* We know that the bi_io_vec layout is the same for
                         * both 'first' and 'i', so we just compare them.
                         * All vec entries are PAGE_SIZE;
                         */
                        for (j = 0; j < vcnt; j++)
                                if (memcmp(page_address(fbio->bi_io_vec[j].bv_page),
                                           page_address(tbio->bi_io_vec[j].bv_page),
                                           PAGE_SIZE))
                                        break;
                        if (j == vcnt)
                                continue;
                        mddev->resync_mismatches += r10_bio->sectors;
                }
                if (test_bit(MD_RECOVERY_CHECK, &mddev->recovery))
                        /* Don't fix anything. */
                        continue;
                /* Ok, we need to write this bio
                 * First we need to fixup bv_offset, bv_len and
                 * bi_vecs, as the read request might have corrupted these
                 */
                tbio->bi_vcnt = vcnt;
                tbio->bi_size = r10_bio->sectors << 9;
                tbio->bi_idx = 0;
                tbio->bi_phys_segments = 0;
                tbio->bi_hw_segments = 0;
                tbio->bi_hw_front_size = 0;
                tbio->bi_hw_back_size = 0;
                tbio->bi_flags &= ~(BIO_POOL_MASK - 1);
                tbio->bi_flags |= 1 << BIO_UPTODATE;
                tbio->bi_next = NULL;
                tbio->bi_rw = WRITE;
                tbio->bi_private = r10_bio;
                tbio->bi_sector = r10_bio->devs[i].addr;

                for (j=0; j < vcnt ; j++) {
                        tbio->bi_io_vec[j].bv_offset = 0;
                        tbio->bi_io_vec[j].bv_len = PAGE_SIZE;

                        memcpy(page_address(tbio->bi_io_vec[j].bv_page),
                               page_address(fbio->bi_io_vec[j].bv_page),
                               PAGE_SIZE);
                }
                tbio->bi_end_io = end_sync_write;

                d = r10_bio->devs[i].devnum;
                atomic_inc(&conf->mirrors[d].rdev->nr_pending);
                atomic_inc(&r10_bio->remaining);
                md_sync_acct(conf->mirrors[d].rdev->bdev, tbio->bi_size >> 9);

                tbio->bi_sector += conf->mirrors[d].rdev->data_offset;
                tbio->bi_bdev = conf->mirrors[d].rdev->bdev;
                generic_make_request(tbio);
        }

done:
        if (atomic_dec_and_test(&r10_bio->remaining)) {
                md_done_sync(mddev, r10_bio->sectors, 1);
                put_buf(r10_bio);
        }
}

/*
 * Now for the recovery code.
 * Recovery happens across physical sectors.
 * We recover all non-is_sync drives by finding the virtual address of
 * each, and then choose a working drive that also has that virt address.
 * There is a separate r10_bio for each non-in_sync drive.
 * Only the first two slots are in use. The first for reading,
 * The second for writing.
 *
 */

static void recovery_request_write(mddev_t *mddev, r10bio_t *r10_bio)
{
        conf_t *conf = mddev_to_conf(mddev);
        int i, d;
        struct bio *bio, *wbio;


        /* move the pages across to the second bio
         * and submit the write request
         */
        bio = r10_bio->devs[0].bio;
        wbio = r10_bio->devs[1].bio;
        for (i=0; i < wbio->bi_vcnt; i++) {
                struct page *p = bio->bi_io_vec[i].bv_page;
                bio->bi_io_vec[i].bv_page = wbio->bi_io_vec[i].bv_page;
                wbio->bi_io_vec[i].bv_page = p;
        }
        d = r10_bio->devs[1].devnum;

        atomic_inc(&conf->mirrors[d].rdev->nr_pending);
        md_sync_acct(conf->mirrors[d].rdev->bdev, wbio->bi_size >> 9);
        if (test_bit(R10BIO_Uptodate, &r10_bio->state))
                generic_make_request(wbio);
        else
                bio_endio(wbio, -EIO);
}


/*
 * This is a kernel thread which:
 *
 *      1.      Retries failed read operations on working mirrors.
 *      2.      Updates the raid superblock when problems encounter.
 *      3.      Performs writes following reads for array synchronising.
 */

static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
{
        int sect = 0; /* Offset from r10_bio->sector */
        int sectors = r10_bio->sectors;
        mdk_rdev_t*rdev;
        while(sectors) {
                int s = sectors;
                int sl = r10_bio->read_slot;
                int success = 0;
                int start;

                if (s > (PAGE_SIZE>>9))
                        s = PAGE_SIZE >> 9;

                rcu_read_lock();
                do {
                        int d = r10_bio->devs[sl].devnum;
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (rdev &&
                            test_bit(In_sync, &rdev->flags)) {
                                atomic_inc(&rdev->nr_pending);
                                rcu_read_unlock();
                                success = sync_page_io(rdev->bdev,
                                                       r10_bio->devs[sl].addr +
                                                       sect + rdev->data_offset,
                                                       s<<9,
                                                       conf->tmppage, READ);
                                rdev_dec_pending(rdev, mddev);
                                rcu_read_lock();
                                if (success)
                                        break;
                        }
                        sl++;
                        if (sl == conf->copies)
                                sl = 0;
                } while (!success && sl != r10_bio->read_slot);
                rcu_read_unlock();

                if (!success) {
                        /* Cannot read from anywhere -- bye bye array */
                        int dn = r10_bio->devs[r10_bio->read_slot].devnum;
                        md_error(mddev, conf->mirrors[dn].rdev);
                        break;
                }

                start = sl;
                /* write it back and re-read */
                rcu_read_lock();
                while (sl != r10_bio->read_slot) {
                        int d;
                        if (sl==0)
                                sl = conf->copies;
                        sl--;
                        d = r10_bio->devs[sl].devnum;
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (rdev &&
                            test_bit(In_sync, &rdev->flags)) {
                                atomic_inc(&rdev->nr_pending);
                                rcu_read_unlock();
                                atomic_add(s, &rdev->corrected_errors);
                                if (sync_page_io(rdev->bdev,
                                                 r10_bio->devs[sl].addr +
                                                 sect + rdev->data_offset,
                                                 s<<9, conf->tmppage, WRITE)
                                    == 0)
                                        /* Well, this device is dead */
                                        md_error(mddev, rdev);
                                rdev_dec_pending(rdev, mddev);
                                rcu_read_lock();
                        }
                }
                sl = start;
                while (sl != r10_bio->read_slot) {
                        int d;
                        if (sl==0)
                                sl = conf->copies;
                        sl--;
                        d = r10_bio->devs[sl].devnum;
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (rdev &&
                            test_bit(In_sync, &rdev->flags)) {
                                char b[BDEVNAME_SIZE];
                                atomic_inc(&rdev->nr_pending);
                                rcu_read_unlock();
                                if (sync_page_io(rdev->bdev,
                                                 r10_bio->devs[sl].addr +
                                                 sect + rdev->data_offset,
                                                 s<<9, conf->tmppage, READ) == 0)
                                        /* Well, this device is dead */
                                        md_error(mddev, rdev);
                                else
                                        printk(KERN_INFO
                                               "raid10:%s: read error corrected"
                                               " (%d sectors at %llu on %s)\n",
                                               mdname(mddev), s,
                                               (unsigned long long)(sect+
                                                    rdev->data_offset),
                                               bdevname(rdev->bdev, b));

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

                sectors -= s;
                sect += s;
        }
}

static void raid10d(mddev_t *mddev)
{
        r10bio_t *r10_bio;
        struct bio *bio;
        unsigned long flags;
        conf_t *conf = mddev_to_conf(mddev);
        struct list_head *head = &conf->retry_list;
        int unplug=0;
        mdk_rdev_t *rdev;

        md_check_recovery(mddev);

        for (;;) {
                char b[BDEVNAME_SIZE];
                spin_lock_irqsave(&conf->device_lock, flags);

                if (conf->pending_bio_list.head) {
                        bio = bio_list_get(&conf->pending_bio_list);
                        blk_remove_plug(mddev->queue);
                        spin_unlock_irqrestore(&conf->device_lock, flags);
                        /* flush any pending bitmap writes to disk before proceeding w/ I/O */
                        bitmap_unplug(mddev->bitmap);

                        while (bio) { /* submit pending writes */
                                struct bio *next = bio->bi_next;
                                bio->bi_next = NULL;
                                generic_make_request(bio);
                                bio = next;
                        }
                        unplug = 1;

                        continue;
                }

                if (list_empty(head))
                        break;
                r10_bio = list_entry(head->prev, r10bio_t, retry_list);
                list_del(head->prev);
                conf->nr_queued--;
                spin_unlock_irqrestore(&conf->device_lock, flags);

                mddev = r10_bio->mddev;
                conf = mddev_to_conf(mddev);
                if (test_bit(R10BIO_IsSync, &r10_bio->state)) {
                        sync_request_write(mddev, r10_bio);
                        unplug = 1;
                } else  if (test_bit(R10BIO_IsRecover, &r10_bio->state)) {
                        recovery_request_write(mddev, r10_bio);
                        unplug = 1;
                } else {
                        int mirror;
                        /* we got a read error. Maybe the drive is bad.  Maybe just
                         * the block and we can fix it.
                         * We freeze all other IO, and try reading the block from
                         * other devices.  When we find one, we re-write
                         * and check it that fixes the read error.
                         * This is all done synchronously while the array is
                         * frozen.
                         */
                        if (mddev->ro == 0) {
                                freeze_array(conf);
                                fix_read_error(conf, mddev, r10_bio);
                                unfreeze_array(conf);
                        }

                        bio = r10_bio->devs[r10_bio->read_slot].bio;
                        r10_bio->devs[r10_bio->read_slot].bio =
                                mddev->ro ? IO_BLOCKED : NULL;
                        mirror = read_balance(conf, r10_bio);
                        if (mirror == -1) {
                                printk(KERN_ALERT "raid10: %s: unrecoverable I/O"
                                       " read error for block %llu\n",
                                       bdevname(bio->bi_bdev,b),
                                       (unsigned long long)r10_bio->sector);
                                raid_end_bio_io(r10_bio);
                                bio_put(bio);
                        } else {
                                const int do_sync = bio_sync(r10_bio->master_bio);
                                bio_put(bio);
                                rdev = conf->mirrors[mirror].rdev;
                                if (printk_ratelimit())
                                        printk(KERN_ERR "raid10: %s: redirecting sector %llu to"
                                               " another mirror\n",
                                               bdevname(rdev->bdev,b),
                                               (unsigned long long)r10_bio->sector);
                                bio = bio_clone(r10_bio->master_bio, GFP_NOIO);
                                r10_bio->devs[r10_bio->read_slot].bio = bio;
                                bio->bi_sector = r10_bio->devs[r10_bio->read_slot].addr
                                        + rdev->data_offset;
                                bio->bi_bdev = rdev->bdev;
                                bio->bi_rw = READ | do_sync;
                                bio->bi_private = r10_bio;
                                bio->bi_end_io = raid10_end_read_request;
                                unplug = 1;
                                generic_make_request(bio);
                        }
                }
        }
        spin_unlock_irqrestore(&conf->device_lock, flags);
        if (unplug)
                unplug_slaves(mddev);
}


static int init_resync(conf_t *conf)
{
        int buffs;

        buffs = RESYNC_WINDOW / RESYNC_BLOCK_SIZE;
        BUG_ON(conf->r10buf_pool);
        conf->r10buf_pool = mempool_create(buffs, r10buf_pool_alloc, r10buf_pool_free, conf);
        if (!conf->r10buf_pool)
                return -ENOMEM;
        conf->next_resync = 0;
        return 0;
}

/*
 * perform a "sync" on one "block"
 *
 * We need to make sure that no normal I/O request - particularly write
 * requests - conflict with active sync requests.
 *
 * This is achieved by tracking pending requests and a 'barrier' concept
 * that can be installed to exclude normal IO requests.
 *
 * Resync and recovery are handled very differently.
 * We differentiate by looking at MD_RECOVERY_SYNC in mddev->recovery.
 *
 * For resync, we iterate over virtual addresses, read all copies,
 * and update if there are differences.  If only one copy is live,
 * skip it.
 * For recovery, we iterate over physical addresses, read a good
 * value for each non-in_sync drive, and over-write.
 *
 * So, for recovery we may have several outstanding complex requests for a
 * given address, one for each out-of-sync device.  We model this by allocating
 * a number of r10_bio structures, one for each out-of-sync device.
 * As we setup these structures, we collect all bio's together into a list
 * which we then process collectively to add pages, and then process again
 * to pass to generic_make_request.
 *
 * The r10_bio structures are linked using a borrowed master_bio pointer.
 * This link is counted in ->remaining.  When the r10_bio that points to NULL
 * has its remaining count decremented to 0, the whole complex operation
 * is complete.
 *
 */

static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, int go_faster)
{
        conf_t *conf = mddev_to_conf(mddev);
        r10bio_t *r10_bio;
        struct bio *biolist = NULL, *bio;
        sector_t max_sector, nr_sectors;
        int disk;
        int i;
        int max_sync;
        int sync_blocks;

        sector_t sectors_skipped = 0;
        int chunks_skipped = 0;

        if (!conf->r10buf_pool)
                if (init_resync(conf))
                        return 0;

 skipped:
        max_sector = mddev->size << 1;
        if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
                max_sector = mddev->resync_max_sectors;
        if (sector_nr >= max_sector) {
                /* If we aborted, we need to abort the
                 * sync on the 'current' bitmap chucks (there can
                 * be several when recovering multiple devices).
                 * as we may have started syncing it but not finished.
                 * We can find the current address in
                 * mddev->curr_resync, but for recovery,
                 * we need to convert that to several
                 * virtual addresses.
                 */
                if (mddev->curr_resync < max_sector) { /* aborted */
                        if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
                                bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
                                                &sync_blocks, 1);
                        else for (i=0; i<conf->raid_disks; i++) {
                                sector_t sect =
                                        raid10_find_virt(conf, mddev->curr_resync, i);
                                bitmap_end_sync(mddev->bitmap, sect,
                                                &sync_blocks, 1);
                        }
                } else /* completed sync */
                        conf->fullsync = 0;

                bitmap_close_sync(mddev->bitmap);
                close_sync(conf);
                *skipped = 1;
                return sectors_skipped;
        }
        if (chunks_skipped >= conf->raid_disks) {
                /* if there has been nothing to do on any drive,
                 * then there is nothing to do at all..
                 */
                *skipped = 1;
                return (max_sector - sector_nr) + sectors_skipped;
        }

        /* make sure whole request will fit in a chunk - if chunks
         * are meaningful
         */
        if (conf->near_copies < conf->raid_disks &&
            max_sector > (sector_nr | conf->chunk_mask))
                max_sector = (sector_nr | conf->chunk_mask) + 1;
        /*
         * If there is non-resync activity waiting for us then
         * put in a delay to throttle resync.
         */
        if (!go_faster && conf->nr_waiting)
                msleep_interruptible(1000);

        /* Again, very different code for resync and recovery.
         * Both must result in an r10bio with a list of bios that
         * have bi_end_io, bi_sector, bi_bdev set,
         * and bi_private set to the r10bio.
         * For recovery, we may actually create several r10bios
         * with 2 bios in each, that correspond to the bios in the main one.
         * In this case, the subordinate r10bios link back through a
         * borrowed master_bio pointer, and the counter in the master
         * includes a ref from each subordinate.
         */
        /* First, we decide what to do and set ->bi_end_io
         * To end_sync_read if we want to read, and
         * end_sync_write if we will want to write.
         */

        max_sync = RESYNC_PAGES << (PAGE_SHIFT-9);
        if (!test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
                /* recovery... the complicated one */
                int i, j, k;
                r10_bio = NULL;

                for (i=0 ; i<conf->raid_disks; i++)
                        if (conf->mirrors[i].rdev &&
                            !test_bit(In_sync, &conf->mirrors[i].rdev->flags)) {
                                int still_degraded = 0;
                                /* want to reconstruct this device */
                                r10bio_t *rb2 = r10_bio;
                                sector_t sect = raid10_find_virt(conf, sector_nr, i);
                                int must_sync;
                                /* Unless we are doing a full sync, we only need
                                 * to recover the block if it is set in the bitmap
                                 */
                                must_sync = bitmap_start_sync(mddev->bitmap, sect,
                                                              &sync_blocks, 1);
                                if (sync_blocks < max_sync)
                                        max_sync = sync_blocks;
                                if (!must_sync &&
                                    !conf->fullsync) {
                                        /* yep, skip the sync_blocks here, but don't assume
                                         * that there will never be anything to do here
                                         */
                                        chunks_skipped = -1;
                                        continue;
                                }

                                r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
                                raise_barrier(conf, rb2 != NULL);
                                atomic_set(&r10_bio->remaining, 0);

                                r10_bio->master_bio = (struct bio*)rb2;
                                if (rb2)
                                        atomic_inc(&rb2->remaining);
                                r10_bio->mddev = mddev;
                                set_bit(R10BIO_IsRecover, &r10_bio->state);
                                r10_bio->sector = sect;

                                raid10_find_phys(conf, r10_bio);
                                /* Need to check if this section will still be
                                 * degraded
                                 */
                                for (j=0; j<conf->copies;j++) {
                                        int d = r10_bio->devs[j].devnum;
                                        if (conf->mirrors[d].rdev == NULL ||
                                            test_bit(Faulty, &conf->mirrors[d].rdev->flags)) {
                                                still_degraded = 1;
                                                break;
                                        }
                                }
                                must_sync = bitmap_start_sync(mddev->bitmap, sect,
                                                              &sync_blocks, still_degraded);

                                for (j=0; j<conf->copies;j++) {
                                        int d = r10_bio->devs[j].devnum;
                                        if (conf->mirrors[d].rdev &&
                                            test_bit(In_sync, &conf->mirrors[d].rdev->flags)) {
                                                /* This is where we read from */
                                                bio = r10_bio->devs[0].bio;
                                                bio->bi_next = biolist;
                                                biolist = bio;
                                                bio->bi_private = r10_bio;
                                                bio->bi_end_io = end_sync_read;
                                                bio->bi_rw = READ;
                                                bio->bi_sector = r10_bio->devs[j].addr +
                                                        conf->mirrors[d].rdev->data_offset;
                                                bio->bi_bdev = conf->mirrors[d].rdev->bdev;
                                                atomic_inc(&conf->mirrors[d].rdev->nr_pending);
                                                atomic_inc(&r10_bio->remaining);
                                                /* and we write to 'i' */

                                                for (k=0; k<conf->copies; k++)
                                                        if (r10_bio->devs[k].devnum == i)
                                                                break;
                                                BUG_ON(k == conf->copies);
                                                bio = r10_bio->devs[1].bio;
                                                bio->bi_next = biolist;
                                                biolist = bio;
                                                bio->bi_private = r10_bio;
                                                bio->bi_end_io = end_sync_write;
                                                bio->bi_rw = WRITE;
                                                bio->bi_sector = r10_bio->devs[k].addr +
                                                        conf->mirrors[i].rdev->data_offset;
                                                bio->bi_bdev = conf->mirrors[i].rdev->bdev;

                                                r10_bio->devs[0].devnum = d;
                                                r10_bio->devs[1].devnum = i;

                                                break;
                                        }
                                }
                                if (j == conf->copies) {
                                        /* Cannot recover, so abort the recovery */
                                        put_buf(r10_bio);
                                        r10_bio = rb2;
                                        if (!test_and_set_bit(MD_RECOVERY_ERR, &mddev->recovery))
                                                printk(KERN_INFO "raid10: %s: insufficient working devices for recovery.\n",
                                                       mdname(mddev));
                                        break;
                                }
                        }
                if (biolist == NULL) {
                        while (r10_bio) {
                                r10bio_t *rb2 = r10_bio;
                                r10_bio = (r10bio_t*) rb2->master_bio;
                                rb2->master_bio = NULL;
                                put_buf(rb2);
                        }
                        goto giveup;
                }
        } else {
                /* resync. Schedule a read for every block at this virt offset */
                int count = 0;

                if (!bitmap_start_sync(mddev->bitmap, sector_nr,
                                       &sync_blocks, mddev->degraded) &&
                    !conf->fullsync && !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery)) {
                        /* We can skip this block */
                        *skipped = 1;
                        return sync_blocks + sectors_skipped;
                }
                if (sync_blocks < max_sync)
                        max_sync = sync_blocks;
                r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);

                r10_bio->mddev = mddev;
                atomic_set(&r10_bio->remaining, 0);
                raise_barrier(conf, 0);
                conf->next_resync = sector_nr;

                r10_bio->master_bio = NULL;
                r10_bio->sector = sector_nr;
                set_bit(R10BIO_IsSync, &r10_bio->state);
                raid10_find_phys(conf, r10_bio);
                r10_bio->sectors = (sector_nr | conf->chunk_mask) - sector_nr +1;

                for (i=0; i<conf->copies; i++) {
                        int d = r10_bio->devs[i].devnum;
                        bio = r10_bio->devs[i].bio;
                        bio->bi_end_io = NULL;
                        clear_bit(BIO_UPTODATE, &bio->bi_flags);
                        if (conf->mirrors[d].rdev == NULL ||
                            test_bit(Faulty, &conf->mirrors[d].rdev->flags))
                                continue;
                        atomic_inc(&conf->mirrors[d].rdev->nr_pending);
                        atomic_inc(&r10_bio->remaining);
                        bio->bi_next = biolist;
                        biolist = bio;
                        bio->bi_private = r10_bio;
                        bio->bi_end_io = end_sync_read;
                        bio->bi_rw = READ;
                        bio->bi_sector = r10_bio->devs[i].addr +
                                conf->mirrors[d].rdev->data_offset;
                        bio->bi_bdev = conf->mirrors[d].rdev->bdev;
                        count++;
                }

                if (count < 2) {
                        for (i=0; i<conf->copies; i++) {
                                int d = r10_bio->devs[i].devnum;
                                if (r10_bio->devs[i].bio->bi_end_io)
                                        rdev_dec_pending(conf->mirrors[d].rdev, mddev);
                        }
                        put_buf(r10_bio);
                        biolist = NULL;
                        goto giveup;
                }
        }

        for (bio = biolist; bio ; bio=bio->bi_next) {

                bio->bi_flags &= ~(BIO_POOL_MASK - 1);
                if (bio->bi_end_io)
                        bio->bi_flags |= 1 << BIO_UPTODATE;
                bio->bi_vcnt = 0;
                bio->bi_idx = 0;
                bio->bi_phys_segments = 0;
                bio->bi_hw_segments = 0;
                bio->bi_size = 0;
        }

        nr_sectors = 0;
        if (sector_nr + max_sync < max_sector)
                max_sector = sector_nr + max_sync;
        do {
                struct page *page;
                int len = PAGE_SIZE;
                disk = 0;
                if (sector_nr + (len>>9) > max_sector)
                        len = (max_sector - sector_nr) << 9;
                if (len == 0)
                        break;
                for (bio= biolist ; bio ; bio=bio->bi_next) {
                        page = bio->bi_io_vec[bio->bi_vcnt].bv_page;
                        if (bio_add_page(bio, page, len, 0) == 0) {
                                /* stop here */
                                struct bio *bio2;
                                bio->bi_io_vec[bio->bi_vcnt].bv_page = page;
                                for (bio2 = biolist; bio2 && bio2 != bio; bio2 = bio2->bi_next) {
                                        /* remove last page from this bio */
                                        bio2->bi_vcnt--;
                                        bio2->bi_size -= len;
                                        bio2->bi_flags &= ~(1<< BIO_SEG_VALID);
                                }
                                goto bio_full;
                        }
                        disk = i;
                }
                nr_sectors += len>>9;
                sector_nr += len>>9;
        } while (biolist->bi_vcnt < RESYNC_PAGES);
 bio_full:
        r10_bio->sectors = nr_sectors;

        while (biolist) {
                bio = biolist;
                biolist = biolist->bi_next;

                bio->bi_next = NULL;
                r10_bio = bio->bi_private;
                r10_bio->sectors = nr_sectors;

                if (bio->bi_end_io == end_sync_read) {
                        md_sync_acct(bio->bi_bdev, nr_sectors);
                        generic_make_request(bio);
                }
        }

        if (sectors_skipped)
                /* pretend they weren't skipped, it makes
                 * no important difference in this case
                 */
                md_done_sync(mddev, sectors_skipped, 1);

        return sectors_skipped + nr_sectors;
 giveup:
        /* There is nowhere to write, so all non-sync
         * drives must be failed, so try the next chunk...
         */
        {
        sector_t sec = max_sector - sector_nr;
        sectors_skipped += sec;
        chunks_skipped ++;
        sector_nr = max_sector;
        goto skipped;
        }
}

static int run(mddev_t *mddev)
{
        conf_t *conf;
        int i, disk_idx;
        mirror_info_t *disk;
        mdk_rdev_t *rdev;
        struct list_head *tmp;
        int nc, fc, fo;
        sector_t stride, size;

        if (mddev->chunk_size == 0) {
                printk(KERN_ERR "md/raid10: non-zero chunk size required.\n");
                return -EINVAL;
        }

        nc = mddev->layout & 255;
        fc = (mddev->layout >> 8) & 255;
        fo = mddev->layout & (1<<16);
        if ((nc*fc) <2 || (nc*fc) > mddev->raid_disks ||
            (mddev->layout >> 17)) {
                printk(KERN_ERR "raid10: %s: unsupported raid10 layout: 0x%8x\n",
                       mdname(mddev), mddev->layout);
                goto out;
        }
        /*
         * copy the already verified devices into our private RAID10
         * bookkeeping area. [whatever we allocate in run(),
         * should be freed in stop()]
         */
        conf = kzalloc(sizeof(conf_t), GFP_KERNEL);
        mddev->private = conf;
        if (!conf) {
                printk(KERN_ERR "raid10: couldn't allocate memory for %s\n",
                        mdname(mddev));
                goto out;
        }
        conf->mirrors = kzalloc(sizeof(struct mirror_info)*mddev->raid_disks,
                                 GFP_KERNEL);
        if (!conf->mirrors) {
                printk(KERN_ERR "raid10: couldn't allocate memory for %s\n",
                       mdname(mddev));
                goto out_free_conf;
        }

        conf->tmppage = alloc_page(GFP_KERNEL);
        if (!conf->tmppage)
                goto out_free_conf;

        conf->mddev = mddev;
        conf->raid_disks = mddev->raid_disks;
        conf->near_copies = nc;
        conf->far_copies = fc;
        conf->copies = nc*fc;
        conf->far_offset = fo;
        conf->chunk_mask = (sector_t)(mddev->chunk_size>>9)-1;
        conf->chunk_shift = ffz(~mddev->chunk_size) - 9;
        size = mddev->size >> (conf->chunk_shift-1);
        sector_div(size, fc);
        size = size * conf->raid_disks;
        sector_div(size, nc);
        /* 'size' is now the number of chunks in the array */
        /* calculate "used chunks per device" in 'stride' */
        stride = size * conf->copies;

        /* We need to round up when dividing by raid_disks to
         * get the stride size.
         */
        stride += conf->raid_disks - 1;
        sector_div(stride, conf->raid_disks);
        mddev->size = stride  << (conf->chunk_shift-1);

        if (fo)
                stride = 1;
        else
                sector_div(stride, fc);
        conf->stride = stride << conf->chunk_shift;

        conf->r10bio_pool = mempool_create(NR_RAID10_BIOS, r10bio_pool_alloc,
                                                r10bio_pool_free, conf);
        if (!conf->r10bio_pool) {
                printk(KERN_ERR "raid10: couldn't allocate memory for %s\n",
                        mdname(mddev));
                goto out_free_conf;
        }

        ITERATE_RDEV(mddev, rdev, tmp) {
                disk_idx = rdev->raid_disk;
                if (disk_idx >= mddev->raid_disks
                    || disk_idx < 0)
                        continue;
                disk = conf->mirrors + disk_idx;

                disk->rdev = rdev;

                blk_queue_stack_limits(mddev->queue,
                                       rdev->bdev->bd_disk->queue);
                /* as we don't honour merge_bvec_fn, we must never risk
                 * violating it, so limit ->max_sector to one PAGE, as
                 * a one page request is never in violation.
                 */
                if (rdev->bdev->bd_disk->queue->merge_bvec_fn &&
                    mddev->queue->max_sectors > (PAGE_SIZE>>9))
                        mddev->queue->max_sectors = (PAGE_SIZE>>9);

                disk->head_position = 0;
        }
        spin_lock_init(&conf->device_lock);
        INIT_LIST_HEAD(&conf->retry_list);

        spin_lock_init(&conf->resync_lock);
        init_waitqueue_head(&conf->wait_barrier);

        /* need to check that every block has at least one working mirror */
        if (!enough(conf)) {
                printk(KERN_ERR "raid10: not enough operational mirrors for %s\n",
                       mdname(mddev));
                goto out_free_conf;
        }

        mddev->degraded = 0;
        for (i = 0; i < conf->raid_disks; i++) {

                disk = conf->mirrors + i;

                if (!disk->rdev ||
                    !test_bit(In_sync, &disk->rdev->flags)) {
                        disk->head_position = 0;
                        mddev->degraded++;
                }
        }


        mddev->thread = md_register_thread(raid10d, mddev, "%s_raid10");
        if (!mddev->thread) {
                printk(KERN_ERR
                       "raid10: couldn't allocate thread for %s\n",
                       mdname(mddev));
                goto out_free_conf;
        }

        printk(KERN_INFO
                "raid10: raid set %s active with %d out of %d devices\n",
                mdname(mddev), mddev->raid_disks - mddev->degraded,
                mddev->raid_disks);
        /*
         * Ok, everything is just fine now
         */
        mddev->array_size = size << (conf->chunk_shift-1);
        mddev->resync_max_sectors = size << conf->chunk_shift;

        mddev->queue->unplug_fn = raid10_unplug;
        mddev->queue->backing_dev_info.congested_fn = raid10_congested;
        mddev->queue->backing_dev_info.congested_data = mddev;

        /* Calculate max read-ahead size.
         * We need to readahead at least twice a whole stripe....
         * maybe...
         */
        {
                int stripe = conf->raid_disks * (mddev->chunk_size / PAGE_SIZE);
                stripe /= conf->near_copies;
                if (mddev->queue->backing_dev_info.ra_pages < 2* stripe)
                        mddev->queue->backing_dev_info.ra_pages = 2* stripe;
        }

        if (conf->near_copies < mddev->raid_disks)
                blk_queue_merge_bvec(mddev->queue, raid10_mergeable_bvec);
        return 0;

out_free_conf:
        if (conf->r10bio_pool)
                mempool_destroy(conf->r10bio_pool);
        safe_put_page(conf->tmppage);
        kfree(conf->mirrors);
        kfree(conf);
        mddev->private = NULL;
out:
        return -EIO;
}

static int stop(mddev_t *mddev)
{
        conf_t *conf = mddev_to_conf(mddev);

        md_unregister_thread(mddev->thread);
        mddev->thread = NULL;
        blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
        if (conf->r10bio_pool)
                mempool_destroy(conf->r10bio_pool);
        kfree(conf->mirrors);
        kfree(conf);
        mddev->private = NULL;
        return 0;
}

static void raid10_quiesce(mddev_t *mddev, int state)
{
        conf_t *conf = mddev_to_conf(mddev);

        switch(state) {
        case 1:
                raise_barrier(conf, 0);
                break;
        case 0:
                lower_barrier(conf);
                break;
        }
        if (mddev->thread) {
                if (mddev->bitmap)
                        mddev->thread->timeout = mddev->bitmap->daemon_sleep * HZ;
                else
                        mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
                md_wakeup_thread(mddev->thread);
        }
}

static struct mdk_personality raid10_personality =
{
        .name           = "raid10",
        .level          = 10,
        .owner          = THIS_MODULE,
        .make_request   = make_request,
        .run            = run,
        .stop           = stop,
        .status         = status,
        .error_handler  = error,
        .hot_add_disk   = raid10_add_disk,
        .hot_remove_disk= raid10_remove_disk,
        .spare_active   = raid10_spare_active,
        .sync_request   = sync_request,
        .quiesce        = raid10_quiesce,
};

static int __init raid_init(void)
{
        return register_md_personality(&raid10_personality);
}

static void raid_exit(void)
{
        unregister_md_personality(&raid10_personality);
}

module_init(raid_init);
module_exit(raid_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS("md-personality-9"); /* RAID10 */
MODULE_ALIAS("md-raid10");
MODULE_ALIAS("md-level-10");