[PATCH] md: improve read speed to raid10 arrays using 'far copies'

[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 <linux/raid/raid10.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)
 *
 * 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 there 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.
 */

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

static void unplug_slaves(mddev_t *mddev);

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 = kmalloc(size, gfp_flags);
        if (r10_bio)
                memset(r10_bio, 0, size);
        else
                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--)
                __free_page(bio->bi_io_vec[i-1].bv_page);
        while (j--)
                for (i = 0; i < RESYNC_PAGES ; i++)
                        __free_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++) {
                                __free_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_put(*bio);
                *bio = NULL;
        }
}

static inline void free_r10bio(r10bio_t *r10_bio)
{
        unsigned long flags;

        conf_t *conf = mddev_to_conf(r10_bio->mddev);

        /*
         * Wake up any possible resync thread that waits for the device
         * to go idle.
         */
        spin_lock_irqsave(&conf->resync_lock, flags);
        if (!--conf->nr_pending) {
                wake_up(&conf->wait_idle);
                wake_up(&conf->wait_resume);
        }
        spin_unlock_irqrestore(&conf->resync_lock, flags);

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

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

        mempool_free(r10_bio, conf->r10buf_pool);

        spin_lock_irqsave(&conf->resync_lock, flags);
        if (!conf->barrier)
                BUG();
        --conf->barrier;
        wake_up(&conf->wait_resume);
        wake_up(&conf->wait_idle);

        if (!--conf->nr_pending) {
                wake_up(&conf->wait_idle);
                wake_up(&conf->wait_resume);
        }
        spin_unlock_irqrestore(&conf->resync_lock, flags);
}

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);
        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, bio->bi_size,
                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 int raid10_end_read_request(struct bio *bio, unsigned int bytes_done, 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);

        if (bio->bi_size)
                return 1;

        slot = r10_bio->read_slot;
        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);
        else
                /*
                 * 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);

        update_head_pos(slot, r10_bio);

        /*
         * we have only one bio on the read side
         */
        if (uptodate)
                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);
        return 0;
}

static int raid10_end_write_request(struct bio *bio, unsigned int bytes_done, 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);

        if (bio->bi_size)
                return 1;

        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);
        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)) {
                md_write_end(r10_bio->mddev);
                raid_end_bio_io(r10_bio);
        }

        rdev_dec_pending(conf->mirrors[dev].rdev, conf->mddev);
        return 0;
}


/*
 * 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. If a block isn't on a device,
 * that entry in the array is set to MaxSector.
 *
 * 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);

        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;

        while (sector > conf->stride) {
                sector -= conf->stride;
                if (dev < conf->near_copies)
                        dev += conf->raid_disks - conf->near_copies;
                else
                        dev -= conf->near_copies;
        }

        offset = sector & conf->chunk_mask;
        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(request_queue_t *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, 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 ||
                       !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 ||
               !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 ||
                    !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);
        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)) {
                        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 raid10_unplug(request_queue_t *q)
{
        unplug_slaves(q->queuedata);
}

static int raid10_issue_flush(request_queue_t *q, struct gendisk *disk,
                             sector_t *error_sector)
{
        mddev_t *mddev = q->queuedata;
        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 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;
}

/*
 * Throttle resync depth, so that we can both get proper overlapping of
 * requests, but are still able to handle normal requests quickly.
 */
#define RESYNC_DEPTH 32

static void device_barrier(conf_t *conf, sector_t sect)
{
        spin_lock_irq(&conf->resync_lock);
        wait_event_lock_irq(conf->wait_idle, !waitqueue_active(&conf->wait_resume),
                            conf->resync_lock, unplug_slaves(conf->mddev));

        if (!conf->barrier++) {
                wait_event_lock_irq(conf->wait_idle, !conf->nr_pending,
                                    conf->resync_lock, unplug_slaves(conf->mddev));
                if (conf->nr_pending)
                        BUG();
        }
        wait_event_lock_irq(conf->wait_resume, conf->barrier < RESYNC_DEPTH,
                            conf->resync_lock, unplug_slaves(conf->mddev));
        conf->next_resync = sect;
        spin_unlock_irq(&conf->resync_lock);
}

static int make_request(request_queue_t *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);

        if (unlikely(bio_barrier(bio))) {
                bio_endio(bio, bio->bi_size, -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, bio->bi_size);
                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.
         */
        spin_lock_irq(&conf->resync_lock);
        wait_event_lock_irq(conf->wait_resume, !conf->barrier, conf->resync_lock, );
        conf->nr_pending++;
        spin_unlock_irq(&conf->resync_lock);

        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;

        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;
                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;
        }
        rcu_read_unlock();

        atomic_set(&r10_bio->remaining, 1);

        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;
                mbio->bi_private = r10_bio;

                atomic_inc(&r10_bio->remaining);
                generic_make_request(mbio);
        }

        if (atomic_dec_and_test(&r10_bio->remaining)) {
                md_write_end(mddev);
                raid_end_bio_io(r10_bio);
        }

        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)
                seq_printf(seq, " %d far-copies", conf->far_copies);

        seq_printf(seq, " [%d/%d] [", conf->raid_disks,
                                                conf->working_disks);
        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->working_disks == 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_bit(In_sync, &rdev->flags)) {
                mddev->degraded++;
                conf->working_disks--;
                /*
                 * if recovery is running, make sure it aborts.
                 */
                set_bit(MD_RECOVERY_ERR, &mddev->recovery);
        }
        clear_bit(In_sync, &rdev->flags);
        set_bit(Faulty, &rdev->flags);
        mddev->sb_dirty = 1;
        printk(KERN_ALERT "raid10: Disk failure on %s, disabling device. \n"
                "       Operation continuing on %d devices\n",
                bdevname(rdev->bdev,b), conf->working_disks);
}

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->working_disks,
                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)
{
        spin_lock_irq(&conf->resync_lock);
        wait_event_lock_irq(conf->wait_resume, !conf->barrier,
                            conf->resync_lock,  unplug_slaves(conf->mddev));
        spin_unlock_irq(&conf->resync_lock);

        if (conf->barrier) BUG();
        if (waitqueue_active(&conf->wait_idle)) BUG();

        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_bit(In_sync, &tmp->rdev->flags)) {
                        conf->working_disks++;
                        mddev->degraded--;
                        set_bit(In_sync, &tmp->rdev->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;

        for (mirror=0; 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;
                        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 int end_sync_read(struct bio *bio, unsigned int bytes_done, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        r10bio_t * r10_bio = (r10bio_t *)(bio->bi_private);
        conf_t *conf = mddev_to_conf(r10_bio->mddev);
        int i,d;

        if (bio->bi_size)
                return 1;

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

static int end_sync_write(struct bio *bio, unsigned int bytes_done, 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;

        if (bio->bi_size)
                return 1;

        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);
        return 0;
}

/*
 * 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=first+1 ; i < conf->copies ; i++) {
                int vcnt, j, d;

                if (!test_bit(BIO_UPTODATE, &r10_bio->devs[i].bio->bi_flags))
                        continue;
                /* 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;
                 */
                tbio = r10_bio->devs[i].bio;
                vcnt = r10_bio->sectors >> (PAGE_SHIFT-9);
                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;
                /* 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);
        generic_make_request(wbio);
}


/*
 * 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 syncronising.
 */

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 (list_empty(head))
                        break;
                r10_bio = list_entry(head->prev, r10bio_t, retry_list);
                list_del(head->prev);
                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;
                        bio = r10_bio->devs[r10_bio->read_slot].bio;
                        r10_bio->devs[r10_bio->read_slot].bio = NULL;
                        bio_put(bio);
                        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);
                        } else {
                                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;
                                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;
        if (conf->r10buf_pool)
                BUG();
        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;

        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) {
                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 && waitqueue_active(&conf->wait_resume))
                msleep_interruptible(1000);
        device_barrier(conf, sector_nr + RESYNC_SECTORS);

        /* 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.
         */

        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)) {
                                /* want to reconstruct this device */
                                r10bio_t *rb2 = r10_bio;

                                r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
                                spin_lock_irq(&conf->resync_lock);
                                conf->nr_pending++;
                                if (rb2) conf->barrier++;
                                spin_unlock_irq(&conf->resync_lock);
                                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 = raid10_find_virt(conf, sector_nr, i);
                                raid10_find_phys(conf, r10_bio);
                                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 = 0;
                                                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;
                                                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 = 1;
                                                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;
                r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);

                spin_lock_irq(&conf->resync_lock);
                conf->nr_pending++;
                spin_unlock_irq(&conf->resync_lock);

                r10_bio->mddev = mddev;
                atomic_set(&r10_bio->remaining, 0);

                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;
                        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 = 0;
                        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;
        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;
        sector_t stride, size;

        if (mddev->level != 10) {
                printk(KERN_ERR "raid10: %s: raid level not set correctly... (%d)\n",
                       mdname(mddev), mddev->level);
                goto out;
        }
        nc = mddev->layout & 255;
        fc = (mddev->layout >> 8) & 255;
        if ((nc*fc) <2 || (nc*fc) > mddev->raid_disks ||
            (mddev->layout >> 16)) {
                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 = kmalloc(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;
        }
        memset(conf, 0, sizeof(*conf));
        conf->mirrors = kmalloc(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;
        }
        memset(conf->mirrors, 0, sizeof(struct mirror_info)*mddev->raid_disks);

        conf->near_copies = nc;
        conf->far_copies = fc;
        conf->copies = nc*fc;
        conf->chunk_mask = (sector_t)(mddev->chunk_size>>9)-1;
        conf->chunk_shift = ffz(~mddev->chunk_size) - 9;
        stride = mddev->size >> (conf->chunk_shift-1);
        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;
                if (!test_bit(Faulty, &rdev->flags) && test_bit(In_sync, &rdev->flags))
                        conf->working_disks++;
        }
        conf->raid_disks = mddev->raid_disks;
        conf->mddev = mddev;
        spin_lock_init(&conf->device_lock);
        INIT_LIST_HEAD(&conf->retry_list);

        spin_lock_init(&conf->resync_lock);
        init_waitqueue_head(&conf->wait_idle);
        init_waitqueue_head(&conf->wait_resume);

        /* 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) {
                        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
         */
        size = conf->stride * conf->raid_disks;
        sector_div(size, conf->near_copies);
        mddev->array_size = size/2;
        mddev->resync_max_sectors = size;

        mddev->queue->unplug_fn = raid10_unplug;
        mddev->queue->issue_flush_fn = raid10_issue_flush;

        /* 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_CACHE_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);
        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 mdk_personality_t raid10_personality =
{
        .name           = "raid10",
        .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,
};

static int __init raid_init(void)
{
        return register_md_personality(RAID10, &raid10_personality);
}

static void raid_exit(void)
{
        unregister_md_personality(RAID10);
}

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