Merge master.kernel.org:/pub/scm/linux/kernel/git/brodo/pcmcia-2.6

[linux-2.6] / drivers / md / raid1.c

/*
 * raid1.c : Multiple Devices driver for Linux
 *
 * Copyright (C) 1999, 2000, 2001 Ingo Molnar, Red Hat
 *
 * Copyright (C) 1996, 1997, 1998 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *
 * RAID-1 management functions.
 *
 * Better read-balancing code written by Mika Kuoppala <miku@iki.fi>, 2000
 *
 * Fixes to reconstruction by Jakob Østergaard" <jakob@ostenfeld.dk>
 * Various fixes by Neil Brown <neilb@cse.unsw.edu.au>
 *
 * Changes by Peter T. Breuer <ptb@it.uc3m.es> 31/1/2003 to support
 * bitmapped intelligence in resync:
 *
 *      - bitmap marked during normal i/o
 *      - bitmap used to skip nondirty blocks during sync
 *
 * Additions to bitmap code, (C) 2003-2004 Paul Clements, SteelEye Technology:
 * - persistent bitmap code
 *
 * 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/raid1.h>
#include <linux/raid/bitmap.h>

#define DEBUG 0
#if DEBUG
#define PRINTK(x...) printk(x)
#else
#define PRINTK(x...)
#endif

/*
 * Number of guaranteed r1bios in case of extreme VM load:
 */
#define NR_RAID1_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 * r1bio_pool_alloc(gfp_t gfp_flags, void *data)
{
        struct pool_info *pi = data;
        r1bio_t *r1_bio;
        int size = offsetof(r1bio_t, bios[pi->raid_disks]);

        /* allocate a r1bio with room for raid_disks entries in the bios array */
        r1_bio = kzalloc(size, gfp_flags);
        if (!r1_bio)
                unplug_slaves(pi->mddev);

        return r1_bio;
}

static void r1bio_pool_free(void *r1_bio, void *data)
{
        kfree(r1_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)

static void * r1buf_pool_alloc(gfp_t gfp_flags, void *data)
{
        struct pool_info *pi = data;
        struct page *page;
        r1bio_t *r1_bio;
        struct bio *bio;
        int i, j;

        r1_bio = r1bio_pool_alloc(gfp_flags, pi);
        if (!r1_bio) {
                unplug_slaves(pi->mddev);
                return NULL;
        }

        /*
         * Allocate bios : 1 for reading, n-1 for writing
         */
        for (j = pi->raid_disks ; j-- ; ) {
                bio = bio_alloc(gfp_flags, RESYNC_PAGES);
                if (!bio)
                        goto out_free_bio;
                r1_bio->bios[j] = bio;
        }
        /*
         * Allocate RESYNC_PAGES data pages and attach them to
         * the first bio.
         * If this is a user-requested check/repair, allocate
         * RESYNC_PAGES for each bio.
         */
        if (test_bit(MD_RECOVERY_REQUESTED, &pi->mddev->recovery))
                j = pi->raid_disks;
        else
                j = 1;
        while(j--) {
                bio = r1_bio->bios[j];
                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;
                }
        }
        /* If not user-requests, copy the page pointers to all bios */
        if (!test_bit(MD_RECOVERY_REQUESTED, &pi->mddev->recovery)) {
                for (i=0; i<RESYNC_PAGES ; i++)
                        for (j=1; j<pi->raid_disks; j++)
                                r1_bio->bios[j]->bi_io_vec[i].bv_page =
                                        r1_bio->bios[0]->bi_io_vec[i].bv_page;
        }

        r1_bio->master_bio = NULL;

        return r1_bio;

out_free_pages:
        for (i=0; i < RESYNC_PAGES ; i++)
                for (j=0 ; j < pi->raid_disks; j++)
                        safe_put_page(r1_bio->bios[j]->bi_io_vec[i].bv_page);
        j = -1;
out_free_bio:
        while ( ++j < pi->raid_disks )
                bio_put(r1_bio->bios[j]);
        r1bio_pool_free(r1_bio, data);
        return NULL;
}

static void r1buf_pool_free(void *__r1_bio, void *data)
{
        struct pool_info *pi = data;
        int i,j;
        r1bio_t *r1bio = __r1_bio;

        for (i = 0; i < RESYNC_PAGES; i++)
                for (j = pi->raid_disks; j-- ;) {
                        if (j == 0 ||
                            r1bio->bios[j]->bi_io_vec[i].bv_page !=
                            r1bio->bios[0]->bi_io_vec[i].bv_page)
                                safe_put_page(r1bio->bios[j]->bi_io_vec[i].bv_page);
                }
        for (i=0 ; i < pi->raid_disks; i++)
                bio_put(r1bio->bios[i]);

        r1bio_pool_free(r1bio, data);
}

static void put_all_bios(conf_t *conf, r1bio_t *r1_bio)
{
        int i;

        for (i = 0; i < conf->raid_disks; i++) {
                struct bio **bio = r1_bio->bios + i;
                if (*bio && *bio != IO_BLOCKED)
                        bio_put(*bio);
                *bio = NULL;
        }
}

static void free_r1bio(r1bio_t *r1_bio)
{
        conf_t *conf = mddev_to_conf(r1_bio->mddev);

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

        put_all_bios(conf, r1_bio);
        mempool_free(r1_bio, conf->r1bio_pool);
}

static void put_buf(r1bio_t *r1_bio)
{
        conf_t *conf = mddev_to_conf(r1_bio->mddev);
        int i;

        for (i=0; i<conf->raid_disks; i++) {
                struct bio *bio = r1_bio->bios[i];
                if (bio->bi_end_io)
                        rdev_dec_pending(conf->mirrors[i].rdev, r1_bio->mddev);
        }

        mempool_free(r1_bio, conf->r1buf_pool);

        lower_barrier(conf);
}

static void reschedule_retry(r1bio_t *r1_bio)
{
        unsigned long flags;
        mddev_t *mddev = r1_bio->mddev;
        conf_t *conf = mddev_to_conf(mddev);

        spin_lock_irqsave(&conf->device_lock, flags);
        list_add(&r1_bio->retry_list, &conf->retry_list);
        conf->nr_queued ++;
        spin_unlock_irqrestore(&conf->device_lock, flags);

        wake_up(&conf->wait_barrier);
        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(r1bio_t *r1_bio)
{
        struct bio *bio = r1_bio->master_bio;

        /* if nobody has done the final endio yet, do it now */
        if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
                PRINTK(KERN_DEBUG "raid1: sync end %s on sectors %llu-%llu\n",
                        (bio_data_dir(bio) == WRITE) ? "write" : "read",
                        (unsigned long long) bio->bi_sector,
                        (unsigned long long) bio->bi_sector +
                                (bio->bi_size >> 9) - 1);

                bio_endio(bio, bio->bi_size,
                        test_bit(R1BIO_Uptodate, &r1_bio->state) ? 0 : -EIO);
        }
        free_r1bio(r1_bio);
}

/*
 * Update disk head position estimator based on IRQ completion info.
 */
static inline void update_head_pos(int disk, r1bio_t *r1_bio)
{
        conf_t *conf = mddev_to_conf(r1_bio->mddev);

        conf->mirrors[disk].head_position =
                r1_bio->sector + (r1_bio->sectors);
}

static int raid1_end_read_request(struct bio *bio, unsigned int bytes_done, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        r1bio_t * r1_bio = (r1bio_t *)(bio->bi_private);
        int mirror;
        conf_t *conf = mddev_to_conf(r1_bio->mddev);

        if (bio->bi_size)
                return 1;
        
        mirror = r1_bio->read_disk;
        /*
         * this branch is our 'one mirror IO has finished' event handler:
         */
        update_head_pos(mirror, r1_bio);

        if (uptodate || conf->working_disks <= 1) {
                /*
                 * Set R1BIO_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.
                 */
                if (uptodate)
                        set_bit(R1BIO_Uptodate, &r1_bio->state);

                raid_end_bio_io(r1_bio);
        } else {
                /*
                 * oops, read error:
                 */
                char b[BDEVNAME_SIZE];
                if (printk_ratelimit())
                        printk(KERN_ERR "raid1: %s: rescheduling sector %llu\n",
                               bdevname(conf->mirrors[mirror].rdev->bdev,b), (unsigned long long)r1_bio->sector);
                reschedule_retry(r1_bio);
        }

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

static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        r1bio_t * r1_bio = (r1bio_t *)(bio->bi_private);
        int mirror, behind = test_bit(R1BIO_BehindIO, &r1_bio->state);
        conf_t *conf = mddev_to_conf(r1_bio->mddev);
        struct bio *to_put = NULL;

        if (bio->bi_size)
                return 1;

        for (mirror = 0; mirror < conf->raid_disks; mirror++)
                if (r1_bio->bios[mirror] == bio)
                        break;

        if (error == -ENOTSUPP && test_bit(R1BIO_Barrier, &r1_bio->state)) {
                set_bit(BarriersNotsupp, &conf->mirrors[mirror].rdev->flags);
                set_bit(R1BIO_BarrierRetry, &r1_bio->state);
                r1_bio->mddev->barriers_work = 0;
        } else {
                /*
                 * this branch is our 'one mirror IO has finished' event handler:
                 */
                r1_bio->bios[mirror] = NULL;
                to_put = bio;
                if (!uptodate) {
                        md_error(r1_bio->mddev, conf->mirrors[mirror].rdev);
                        /* an I/O failed, we can't clear the bitmap */
                        set_bit(R1BIO_Degraded, &r1_bio->state);
                } else
                        /*
                         * Set R1BIO_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(R1BIO_Uptodate, &r1_bio->state);

                update_head_pos(mirror, r1_bio);

                if (behind) {
                        if (test_bit(WriteMostly, &conf->mirrors[mirror].rdev->flags))
                                atomic_dec(&r1_bio->behind_remaining);

                        /* In behind mode, we ACK the master bio once the I/O has safely
                         * reached all non-writemostly disks. Setting the Returned bit
                         * ensures that this gets done only once -- we don't ever want to
                         * return -EIO here, instead we'll wait */

                        if (atomic_read(&r1_bio->behind_remaining) >= (atomic_read(&r1_bio->remaining)-1) &&
                            test_bit(R1BIO_Uptodate, &r1_bio->state)) {
                                /* Maybe we can return now */
                                if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
                                        struct bio *mbio = r1_bio->master_bio;
                                        PRINTK(KERN_DEBUG "raid1: behind end write sectors %llu-%llu\n",
                                               (unsigned long long) mbio->bi_sector,
                                               (unsigned long long) mbio->bi_sector +
                                               (mbio->bi_size >> 9) - 1);
                                        bio_endio(mbio, mbio->bi_size, 0);
                                }
                        }
                }
        }
        /*
         *
         * Let's see if all mirrored write operations have finished
         * already.
         */
        if (atomic_dec_and_test(&r1_bio->remaining)) {
                if (test_bit(R1BIO_BarrierRetry, &r1_bio->state)) {
                        reschedule_retry(r1_bio);
                        /* Don't dec_pending yet, we want to hold
                         * the reference over the retry
                         */
                        goto out;
                }
                if (test_bit(R1BIO_BehindIO, &r1_bio->state)) {
                        /* free extra copy of the data pages */
                        int i = bio->bi_vcnt;
                        while (i--)
                                safe_put_page(bio->bi_io_vec[i].bv_page);
                }
                /* clear the bitmap if all writes complete successfully */
                bitmap_endwrite(r1_bio->mddev->bitmap, r1_bio->sector,
                                r1_bio->sectors,
                                !test_bit(R1BIO_Degraded, &r1_bio->state),
                                behind);
                md_write_end(r1_bio->mddev);
                raid_end_bio_io(r1_bio);
        }

        rdev_dec_pending(conf->mirrors[mirror].rdev, conf->mddev);
 out:
        if (to_put)
                bio_put(to_put);

        return 0;
}


/*
 * 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.
 */
static int read_balance(conf_t *conf, r1bio_t *r1_bio)
{
        const unsigned long this_sector = r1_bio->sector;
        int new_disk = conf->last_used, disk = new_disk;
        int wonly_disk = -1;
        const int sectors = r1_bio->sectors;
        sector_t new_distance, current_distance;
        mdk_rdev_t *rdev;

        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.
         */
 retry:
        if (conf->mddev->recovery_cp < MaxSector &&
            (this_sector + sectors >= conf->next_resync)) {
                /* Choose the first operation device, for consistancy */
                new_disk = 0;

                for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
                     r1_bio->bios[new_disk] == IO_BLOCKED ||
                     !rdev || !test_bit(In_sync, &rdev->flags)
                             || test_bit(WriteMostly, &rdev->flags);
                     rdev = rcu_dereference(conf->mirrors[++new_disk].rdev)) {

                        if (rdev && test_bit(In_sync, &rdev->flags) &&
                                r1_bio->bios[new_disk] != IO_BLOCKED)
                                wonly_disk = new_disk;

                        if (new_disk == conf->raid_disks - 1) {
                                new_disk = wonly_disk;
                                break;
                        }
                }
                goto rb_out;
        }


        /* make sure the disk is operational */
        for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
             r1_bio->bios[new_disk] == IO_BLOCKED ||
             !rdev || !test_bit(In_sync, &rdev->flags) ||
                     test_bit(WriteMostly, &rdev->flags);
             rdev = rcu_dereference(conf->mirrors[new_disk].rdev)) {

                if (rdev && test_bit(In_sync, &rdev->flags) &&
                    r1_bio->bios[new_disk] != IO_BLOCKED)
                        wonly_disk = new_disk;

                if (new_disk <= 0)
                        new_disk = conf->raid_disks;
                new_disk--;
                if (new_disk == disk) {
                        new_disk = wonly_disk;
                        break;
                }
        }

        if (new_disk < 0)
                goto rb_out;

        disk = new_disk;
        /* now disk == new_disk == starting point for search */

        /*
         * Don't change to another disk for sequential reads:
         */
        if (conf->next_seq_sect == this_sector)
                goto rb_out;
        if (this_sector == conf->mirrors[new_disk].head_position)
                goto rb_out;

        current_distance = abs(this_sector - conf->mirrors[disk].head_position);

        /* Find the disk whose head is closest */

        do {
                if (disk <= 0)
                        disk = conf->raid_disks;
                disk--;

                rdev = rcu_dereference(conf->mirrors[disk].rdev);

                if (!rdev || r1_bio->bios[disk] == IO_BLOCKED ||
                    !test_bit(In_sync, &rdev->flags) ||
                    test_bit(WriteMostly, &rdev->flags))
                        continue;

                if (!atomic_read(&rdev->nr_pending)) {
                        new_disk = disk;
                        break;
                }
                new_distance = abs(this_sector - conf->mirrors[disk].head_position);
                if (new_distance < current_distance) {
                        current_distance = new_distance;
                        new_disk = disk;
                }
        } while (disk != conf->last_used);

 rb_out:


        if (new_disk >= 0) {
                rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
                if (!rdev)
                        goto retry;
                atomic_inc(&rdev->nr_pending);
                if (!test_bit(In_sync, &rdev->flags)) {
                        /* cannot risk returning a device that failed
                         * before we inc'ed nr_pending
                         */
                        rdev_dec_pending(rdev, conf->mddev);
                        goto retry;
                }
                conf->next_seq_sect = this_sector + sectors;
                conf->last_used = new_disk;
        }
        rcu_read_unlock();

        return new_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 raid1_unplug(request_queue_t *q)
{
        mddev_t *mddev = q->queuedata;

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

static int raid1_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;
}

/* 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)
{
        spin_lock_irq(&conf->resync_lock);

        /* Wait until no block IO is waiting */
        wait_event_lock_irq(conf->wait_barrier, !conf->nr_waiting,
                            conf->resync_lock,
                            raid1_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,
                            raid1_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,
                                    raid1_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 quite.
         * 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,
                            raid1_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);
}


/* duplicate the data pages for behind I/O */
static struct page **alloc_behind_pages(struct bio *bio)
{
        int i;
        struct bio_vec *bvec;
        struct page **pages = kzalloc(bio->bi_vcnt * sizeof(struct page *),
                                        GFP_NOIO);
        if (unlikely(!pages))
                goto do_sync_io;

        bio_for_each_segment(bvec, bio, i) {
                pages[i] = alloc_page(GFP_NOIO);
                if (unlikely(!pages[i]))
                        goto do_sync_io;
                memcpy(kmap(pages[i]) + bvec->bv_offset,
                        kmap(bvec->bv_page) + bvec->bv_offset, bvec->bv_len);
                kunmap(pages[i]);
                kunmap(bvec->bv_page);
        }

        return pages;

do_sync_io:
        if (pages)
                for (i = 0; i < bio->bi_vcnt && pages[i]; i++)
                        put_page(pages[i]);
        kfree(pages);
        PRINTK("%dB behind alloc failed, doing sync I/O\n", bio->bi_size);
        return NULL;
}

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;
        r1bio_t *r1_bio;
        struct bio *read_bio;
        int i, targets = 0, disks;
        mdk_rdev_t *rdev;
        struct bitmap *bitmap = mddev->bitmap;
        unsigned long flags;
        struct bio_list bl;
        struct page **behind_pages = NULL;
        const int rw = bio_data_dir(bio);
        int do_barriers;

        if (unlikely(!mddev->barriers_work && bio_barrier(bio))) {
                bio_endio(bio, bio->bi_size, -EOPNOTSUPP);
                return 0;
        }

        /*
         * 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.
         */
        md_write_start(mddev, bio); /* wait on superblock update early */

        wait_barrier(conf);

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

        /*
         * make_request() can abort the operation when READA is being
         * used and no empty request is available.
         *
         */
        r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);

        r1_bio->master_bio = bio;
        r1_bio->sectors = bio->bi_size >> 9;
        r1_bio->state = 0;
        r1_bio->mddev = mddev;
        r1_bio->sector = bio->bi_sector;

        if (rw == READ) {
                /*
                 * read balancing logic:
                 */
                int rdisk = read_balance(conf, r1_bio);

                if (rdisk < 0) {
                        /* couldn't find anywhere to read from */
                        raid_end_bio_io(r1_bio);
                        return 0;
                }
                mirror = conf->mirrors + rdisk;

                r1_bio->read_disk = rdisk;

                read_bio = bio_clone(bio, GFP_NOIO);

                r1_bio->bios[rdisk] = read_bio;

                read_bio->bi_sector = r1_bio->sector + mirror->rdev->data_offset;
                read_bio->bi_bdev = mirror->rdev->bdev;
                read_bio->bi_end_io = raid1_end_read_request;
                read_bio->bi_rw = READ;
                read_bio->bi_private = r1_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
         */
        disks = conf->raid_disks;
#if 0
        { static int first=1;
        if (first) printk("First Write sector %llu disks %d\n",
                          (unsigned long long)r1_bio->sector, disks);
        first = 0;
        }
#endif
        rcu_read_lock();
        for (i = 0;  i < disks; i++) {
                if ((rdev=rcu_dereference(conf->mirrors[i].rdev)) != NULL &&
                    !test_bit(Faulty, &rdev->flags)) {
                        atomic_inc(&rdev->nr_pending);
                        if (test_bit(Faulty, &rdev->flags)) {
                                rdev_dec_pending(rdev, mddev);
                                r1_bio->bios[i] = NULL;
                        } else
                                r1_bio->bios[i] = bio;
                        targets++;
                } else
                        r1_bio->bios[i] = NULL;
        }
        rcu_read_unlock();

        BUG_ON(targets == 0); /* we never fail the last device */

        if (targets < conf->raid_disks) {
                /* array is degraded, we will not clear the bitmap
                 * on I/O completion (see raid1_end_write_request) */
                set_bit(R1BIO_Degraded, &r1_bio->state);
        }

        /* do behind I/O ? */
        if (bitmap &&
            atomic_read(&bitmap->behind_writes) < bitmap->max_write_behind &&
            (behind_pages = alloc_behind_pages(bio)) != NULL)
                set_bit(R1BIO_BehindIO, &r1_bio->state);

        atomic_set(&r1_bio->remaining, 0);
        atomic_set(&r1_bio->behind_remaining, 0);

        do_barriers = bio_barrier(bio);
        if (do_barriers)
                set_bit(R1BIO_Barrier, &r1_bio->state);

        bio_list_init(&bl);
        for (i = 0; i < disks; i++) {
                struct bio *mbio;
                if (!r1_bio->bios[i])
                        continue;

                mbio = bio_clone(bio, GFP_NOIO);
                r1_bio->bios[i] = mbio;

                mbio->bi_sector = r1_bio->sector + conf->mirrors[i].rdev->data_offset;
                mbio->bi_bdev = conf->mirrors[i].rdev->bdev;
                mbio->bi_end_io = raid1_end_write_request;
                mbio->bi_rw = WRITE | do_barriers;
                mbio->bi_private = r1_bio;

                if (behind_pages) {
                        struct bio_vec *bvec;
                        int j;

                        /* Yes, I really want the '__' version so that
                         * we clear any unused pointer in the io_vec, rather
                         * than leave them unchanged.  This is important
                         * because when we come to free the pages, we won't
                         * know the originial bi_idx, so we just free
                         * them all
                         */
                        __bio_for_each_segment(bvec, mbio, j, 0)
                                bvec->bv_page = behind_pages[j];
                        if (test_bit(WriteMostly, &conf->mirrors[i].rdev->flags))
                                atomic_inc(&r1_bio->behind_remaining);
                }

                atomic_inc(&r1_bio->remaining);

                bio_list_add(&bl, mbio);
        }
        kfree(behind_pages); /* the behind pages are attached to the bios now */

        bitmap_startwrite(bitmap, bio->bi_sector, r1_bio->sectors,
                                test_bit(R1BIO_BehindIO, &r1_bio->state));
        spin_lock_irqsave(&conf->device_lock, flags);
        bio_list_merge(&conf->pending_bio_list, &bl);
        bio_list_init(&bl);

        blk_plug_device(mddev->queue);
        spin_unlock_irqrestore(&conf->device_lock, flags);

#if 0
        while ((bio = bio_list_pop(&bl)) != NULL)
                generic_make_request(bio);
#endif

        return 0;
}

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

        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, act as though we were just a
                 * normal single drive
                 */
                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 "raid1: 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("RAID1 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)
{
        wait_barrier(conf);
        allow_barrier(conf);

        mempool_destroy(conf->r1buf_pool);
        conf->r1buf_pool = NULL;
}

static int raid1_spare_active(mddev_t *mddev)
{
        int i;
        conf_t *conf = mddev->private;
        mirror_info_t *tmp;

        /*
         * Find all failed disks within the RAID1 configuration 
         * and mark them readable
         */
        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 raid1_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
{
        conf_t *conf = mddev->private;
        int found = 0;
        int mirror = 0;
        mirror_info_t *p;

        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))
                                blk_queue_max_sectors(mddev->queue, PAGE_SIZE>>9);

                        p->head_position = 0;
                        rdev->raid_disk = mirror;
                        found = 1;
                        /* As all devices are equivalent, we don't need a full recovery
                         * if this was recently any drive of the array
                         */
                        if (rdev->saved_raid_disk < 0)
                                conf->fullsync = 1;
                        rcu_assign_pointer(p->rdev, rdev);
                        break;
                }

        print_conf(conf);
        return found;
}

static int raid1_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)
{
        r1bio_t * r1_bio = (r1bio_t *)(bio->bi_private);
        int i;

        if (bio->bi_size)
                return 1;

        for (i=r1_bio->mddev->raid_disks; i--; )
                if (r1_bio->bios[i] == bio)
                        break;
        BUG_ON(i < 0);
        update_head_pos(i, r1_bio);
        /*
         * we have read a block, now it needs to be re-written,
         * or re-read if the read failed.
         * We don't do much here, just schedule handling by raid1d
         */
        if (test_bit(BIO_UPTODATE, &bio->bi_flags))
                set_bit(R1BIO_Uptodate, &r1_bio->state);

        if (atomic_dec_and_test(&r1_bio->remaining))
                reschedule_retry(r1_bio);
        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);
        r1bio_t * r1_bio = (r1bio_t *)(bio->bi_private);
        mddev_t *mddev = r1_bio->mddev;
        conf_t *conf = mddev_to_conf(mddev);
        int i;
        int mirror=0;

        if (bio->bi_size)
                return 1;

        for (i = 0; i < conf->raid_disks; i++)
                if (r1_bio->bios[i] == bio) {
                        mirror = i;
                        break;
                }
        if (!uptodate) {
                int sync_blocks = 0;
                sector_t s = r1_bio->sector;
                long sectors_to_go = r1_bio->sectors;
                /* make sure these bits doesn't get cleared. */
                do {
                        bitmap_end_sync(mddev->bitmap, r1_bio->sector,
                                        &sync_blocks, 1);
                        s += sync_blocks;
                        sectors_to_go -= sync_blocks;
                } while (sectors_to_go > 0);
                md_error(mddev, conf->mirrors[mirror].rdev);
        }

        update_head_pos(mirror, r1_bio);

        if (atomic_dec_and_test(&r1_bio->remaining)) {
                md_done_sync(mddev, r1_bio->sectors, uptodate);
                put_buf(r1_bio);
        }
        return 0;
}

static void sync_request_write(mddev_t *mddev, r1bio_t *r1_bio)
{
        conf_t *conf = mddev_to_conf(mddev);
        int i;
        int disks = conf->raid_disks;
        struct bio *bio, *wbio;

        bio = r1_bio->bios[r1_bio->read_disk];


        if (test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery)) {
                /* We have read all readable devices.  If we haven't
                 * got the block, then there is no hope left.
                 * If we have, then we want to do a comparison
                 * and skip the write if everything is the same.
                 * If any blocks failed to read, then we need to
                 * attempt an over-write
                 */
                int primary;
                if (!test_bit(R1BIO_Uptodate, &r1_bio->state)) {
                        for (i=0; i<mddev->raid_disks; i++)
                                if (r1_bio->bios[i]->bi_end_io == end_sync_read)
                                        md_error(mddev, conf->mirrors[i].rdev);

                        md_done_sync(mddev, r1_bio->sectors, 1);
                        put_buf(r1_bio);
                        return;
                }
                for (primary=0; primary<mddev->raid_disks; primary++)
                        if (r1_bio->bios[primary]->bi_end_io == end_sync_read &&
                            test_bit(BIO_UPTODATE, &r1_bio->bios[primary]->bi_flags)) {
                                r1_bio->bios[primary]->bi_end_io = NULL;
                                rdev_dec_pending(conf->mirrors[primary].rdev, mddev);
                                break;
                        }
                r1_bio->read_disk = primary;
                for (i=0; i<mddev->raid_disks; i++)
                        if (r1_bio->bios[i]->bi_end_io == end_sync_read &&
                            test_bit(BIO_UPTODATE, &r1_bio->bios[i]->bi_flags)) {
                                int j;
                                int vcnt = r1_bio->sectors >> (PAGE_SHIFT- 9);
                                struct bio *pbio = r1_bio->bios[primary];
                                struct bio *sbio = r1_bio->bios[i];
                                for (j = vcnt; j-- ; )
                                        if (memcmp(page_address(pbio->bi_io_vec[j].bv_page),
                                                   page_address(sbio->bi_io_vec[j].bv_page),
                                                   PAGE_SIZE))
                                                break;
                                if (j >= 0)
                                        mddev->resync_mismatches += r1_bio->sectors;
                                if (j < 0 || test_bit(MD_RECOVERY_CHECK, &mddev->recovery)) {
                                        sbio->bi_end_io = NULL;
                                        rdev_dec_pending(conf->mirrors[i].rdev, mddev);
                                } else {
                                        /* fixup the bio for reuse */
                                        sbio->bi_vcnt = vcnt;
                                        sbio->bi_size = r1_bio->sectors << 9;
                                        sbio->bi_idx = 0;
                                        sbio->bi_phys_segments = 0;
                                        sbio->bi_hw_segments = 0;
                                        sbio->bi_hw_front_size = 0;
                                        sbio->bi_hw_back_size = 0;
                                        sbio->bi_flags &= ~(BIO_POOL_MASK - 1);
                                        sbio->bi_flags |= 1 << BIO_UPTODATE;
                                        sbio->bi_next = NULL;
                                        sbio->bi_sector = r1_bio->sector +
                                                conf->mirrors[i].rdev->data_offset;
                                        sbio->bi_bdev = conf->mirrors[i].rdev->bdev;
                                }
                        }
        }
        if (!test_bit(R1BIO_Uptodate, &r1_bio->state)) {
                /* ouch - failed to read all of that.
                 * Try some synchronous reads of other devices to get
                 * good data, much like with normal read errors.  Only
                 * read into the pages we already have so they we don't
                 * need to re-issue the read request.
                 * We don't need to freeze the array, because being in an
                 * active sync request, there is no normal IO, and
                 * no overlapping syncs.
                 */
                sector_t sect = r1_bio->sector;
                int sectors = r1_bio->sectors;
                int idx = 0;

                while(sectors) {
                        int s = sectors;
                        int d = r1_bio->read_disk;
                        int success = 0;
                        mdk_rdev_t *rdev;

                        if (s > (PAGE_SIZE>>9))
                                s = PAGE_SIZE >> 9;
                        do {
                                if (r1_bio->bios[d]->bi_end_io == end_sync_read) {
                                        rdev = conf->mirrors[d].rdev;
                                        if (sync_page_io(rdev->bdev,
                                                         sect + rdev->data_offset,
                                                         s<<9,
                                                         bio->bi_io_vec[idx].bv_page,
                                                         READ)) {
                                                success = 1;
                                                break;
                                        }
                                }
                                d++;
                                if (d == conf->raid_disks)
                                        d = 0;
                        } while (!success && d != r1_bio->read_disk);

                        if (success) {
                                int start = d;
                                /* write it back and re-read */
                                set_bit(R1BIO_Uptodate, &r1_bio->state);
                                while (d != r1_bio->read_disk) {
                                        if (d == 0)
                                                d = conf->raid_disks;
                                        d--;
                                        if (r1_bio->bios[d]->bi_end_io != end_sync_read)
                                                continue;
                                        rdev = conf->mirrors[d].rdev;
                                        atomic_add(s, &rdev->corrected_errors);
                                        if (sync_page_io(rdev->bdev,
                                                         sect + rdev->data_offset,
                                                         s<<9,
                                                         bio->bi_io_vec[idx].bv_page,
                                                         WRITE) == 0)
                                                md_error(mddev, rdev);
                                }
                                d = start;
                                while (d != r1_bio->read_disk) {
                                        if (d == 0)
                                                d = conf->raid_disks;
                                        d--;
                                        if (r1_bio->bios[d]->bi_end_io != end_sync_read)
                                                continue;
                                        rdev = conf->mirrors[d].rdev;
                                        if (sync_page_io(rdev->bdev,
                                                         sect + rdev->data_offset,
                                                         s<<9,
                                                         bio->bi_io_vec[idx].bv_page,
                                                         READ) == 0)
                                                md_error(mddev, rdev);
                                }
                        } else {
                                char b[BDEVNAME_SIZE];
                                /* Cannot read from anywhere, array is toast */
                                md_error(mddev, conf->mirrors[r1_bio->read_disk].rdev);
                                printk(KERN_ALERT "raid1: %s: unrecoverable I/O read error"
                                       " for block %llu\n",
                                       bdevname(bio->bi_bdev,b),
                                       (unsigned long long)r1_bio->sector);
                                md_done_sync(mddev, r1_bio->sectors, 0);
                                put_buf(r1_bio);
                                return;
                        }
                        sectors -= s;
                        sect += s;
                        idx ++;
                }
        }

        /*
         * schedule writes
         */
        atomic_set(&r1_bio->remaining, 1);
        for (i = 0; i < disks ; i++) {
                wbio = r1_bio->bios[i];
                if (wbio->bi_end_io == NULL ||
                    (wbio->bi_end_io == end_sync_read &&
                     (i == r1_bio->read_disk ||
                      !test_bit(MD_RECOVERY_SYNC, &mddev->recovery))))
                        continue;

                wbio->bi_rw = WRITE;
                wbio->bi_end_io = end_sync_write;
                atomic_inc(&r1_bio->remaining);
                md_sync_acct(conf->mirrors[i].rdev->bdev, wbio->bi_size >> 9);

                generic_make_request(wbio);
        }

        if (atomic_dec_and_test(&r1_bio->remaining)) {
                /* if we're here, all write(s) have completed, so clean up */
                md_done_sync(mddev, r1_bio->sectors, 1);
                put_buf(r1_bio);
        }
}

/*
 * 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 raid1d(mddev_t *mddev)
{
        r1bio_t *r1_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 */
                        if (bitmap_unplug(mddev->bitmap) != 0)
                                printk("%s: bitmap file write failed!\n", mdname(mddev));

                        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;
                r1_bio = list_entry(head->prev, r1bio_t, retry_list);
                list_del(head->prev);
                conf->nr_queued--;
                spin_unlock_irqrestore(&conf->device_lock, flags);

                mddev = r1_bio->mddev;
                conf = mddev_to_conf(mddev);
                if (test_bit(R1BIO_IsSync, &r1_bio->state)) {
                        sync_request_write(mddev, r1_bio);
                        unplug = 1;
                } else if (test_bit(R1BIO_BarrierRetry, &r1_bio->state)) {
                        /* some requests in the r1bio were BIO_RW_BARRIER
                         * requests which failed with -ENOTSUPP.  Hohumm..
                         * Better resubmit without the barrier.
                         * We know which devices to resubmit for, because
                         * all others have had their bios[] entry cleared.
                         */
                        int i;
                        clear_bit(R1BIO_BarrierRetry, &r1_bio->state);
                        clear_bit(R1BIO_Barrier, &r1_bio->state);
                        for (i=0; i < conf->raid_disks; i++)
                                if (r1_bio->bios[i])
                                        atomic_inc(&r1_bio->remaining);
                        for (i=0; i < conf->raid_disks; i++)
                                if (r1_bio->bios[i]) {
                                        struct bio_vec *bvec;
                                        int j;

                                        bio = bio_clone(r1_bio->master_bio, GFP_NOIO);
                                        /* copy pages from the failed bio, as
                                         * this might be a write-behind device */
                                        __bio_for_each_segment(bvec, bio, j, 0)
                                                bvec->bv_page = bio_iovec_idx(r1_bio->bios[i], j)->bv_page;
                                        bio_put(r1_bio->bios[i]);
                                        bio->bi_sector = r1_bio->sector +
                                                conf->mirrors[i].rdev->data_offset;
                                        bio->bi_bdev = conf->mirrors[i].rdev->bdev;
                                        bio->bi_end_io = raid1_end_write_request;
                                        bio->bi_rw = WRITE;
                                        bio->bi_private = r1_bio;
                                        r1_bio->bios[i] = bio;
                                        generic_make_request(bio);
                                }
                } else {
                        int disk;

                        /* 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
                         */
                        sector_t sect = r1_bio->sector;
                        int sectors = r1_bio->sectors;
                        freeze_array(conf);
                        if (mddev->ro == 0) while(sectors) {
                                int s = sectors;
                                int d = r1_bio->read_disk;
                                int success = 0;

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

                                do {
                                        rdev = conf->mirrors[d].rdev;
                                        if (rdev &&
                                            test_bit(In_sync, &rdev->flags) &&
                                            sync_page_io(rdev->bdev,
                                                         sect + rdev->data_offset,
                                                         s<<9,
                                                         conf->tmppage, READ))
                                                success = 1;
                                        else {
                                                d++;
                                                if (d == conf->raid_disks)
                                                        d = 0;
                                        }
                                } while (!success && d != r1_bio->read_disk);

                                if (success) {
                                        /* write it back and re-read */
                                        int start = d;
                                        while (d != r1_bio->read_disk) {
                                                if (d==0)
                                                        d = conf->raid_disks;
                                                d--;
                                                rdev = conf->mirrors[d].rdev;
                                                atomic_add(s, &rdev->corrected_errors);
                                                if (rdev &&
                                                    test_bit(In_sync, &rdev->flags)) {
                                                        if (sync_page_io(rdev->bdev,
                                                                         sect + rdev->data_offset,
                                                                         s<<9, conf->tmppage, WRITE) == 0)
                                                                /* Well, this device is dead */
                                                                md_error(mddev, rdev);
                                                }
                                        }
                                        d = start;
                                        while (d != r1_bio->read_disk) {
                                                if (d==0)
                                                        d = conf->raid_disks;
                                                d--;
                                                rdev = conf->mirrors[d].rdev;
                                                if (rdev &&
                                                    test_bit(In_sync, &rdev->flags)) {
                                                        if (sync_page_io(rdev->bdev,
                                                                         sect + rdev->data_offset,
                                                                         s<<9, conf->tmppage, READ) == 0)
                                                                /* Well, this device is dead */
                                                                md_error(mddev, rdev);
                                                }
                                        }
                                } else {
                                        /* Cannot read from anywhere -- bye bye array */
                                        md_error(mddev, conf->mirrors[r1_bio->read_disk].rdev);
                                        break;
                                }
                                sectors -= s;
                                sect += s;
                        }

                        unfreeze_array(conf);

                        bio = r1_bio->bios[r1_bio->read_disk];
                        if ((disk=read_balance(conf, r1_bio)) == -1) {
                                printk(KERN_ALERT "raid1: %s: unrecoverable I/O"
                                       " read error for block %llu\n",
                                       bdevname(bio->bi_bdev,b),
                                       (unsigned long long)r1_bio->sector);
                                raid_end_bio_io(r1_bio);
                        } else {
                                r1_bio->bios[r1_bio->read_disk] =
                                        mddev->ro ? IO_BLOCKED : NULL;
                                r1_bio->read_disk = disk;
                                bio_put(bio);
                                bio = bio_clone(r1_bio->master_bio, GFP_NOIO);
                                r1_bio->bios[r1_bio->read_disk] = bio;
                                rdev = conf->mirrors[disk].rdev;
                                if (printk_ratelimit())
                                        printk(KERN_ERR "raid1: %s: redirecting sector %llu to"
                                               " another mirror\n",
                                               bdevname(rdev->bdev,b),
                                               (unsigned long long)r1_bio->sector);
                                bio->bi_sector = r1_bio->sector + rdev->data_offset;
                                bio->bi_bdev = rdev->bdev;
                                bio->bi_end_io = raid1_end_read_request;
                                bio->bi_rw = READ;
                                bio->bi_private = r1_bio;
                                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->r1buf_pool)
                BUG();
        conf->r1buf_pool = mempool_create(buffs, r1buf_pool_alloc, r1buf_pool_free,
                                          conf->poolinfo);
        if (!conf->r1buf_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.
 */

static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, int go_faster)
{
        conf_t *conf = mddev_to_conf(mddev);
        r1bio_t *r1_bio;
        struct bio *bio;
        sector_t max_sector, nr_sectors;
        int disk = -1;
        int i;
        int wonly = -1;
        int write_targets = 0, read_targets = 0;
        int sync_blocks;
        int still_degraded = 0;

        if (!conf->r1buf_pool)
        {
/*
                printk("sync start - bitmap %p\n", mddev->bitmap);
*/
                if (init_resync(conf))
                        return 0;
        }

        max_sector = mddev->size << 1;
        if (sector_nr >= max_sector) {
                /* If we aborted, we need to abort the
                 * sync on the 'current' bitmap chunk (there will
                 * only be one in raid1 resync.
                 * We can find the current addess in mddev->curr_resync
                 */
                if (mddev->curr_resync < max_sector) /* aborted */
                        bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
                                                &sync_blocks, 1);
                else /* completed sync */
                        conf->fullsync = 0;

                bitmap_close_sync(mddev->bitmap);
                close_sync(conf);
                return 0;
        }

        /* before building a request, check if we can skip these blocks..
         * This call the bitmap_start_sync doesn't actually record anything
         */
        if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
            !conf->fullsync && !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery)) {
                /* We can skip this block, and probably several more */
                *skipped = 1;
                return sync_blocks;
        }
        /*
         * If there is non-resync activity waiting for a turn,
         * and resync is going fast enough,
         * then let it though before starting on this new sync request.
         */
        if (!go_faster && conf->nr_waiting)
                msleep_interruptible(1000);

        raise_barrier(conf);

        conf->next_resync = sector_nr;

        r1_bio = mempool_alloc(conf->r1buf_pool, GFP_NOIO);
        rcu_read_lock();
        /*
         * If we get a correctably read error during resync or recovery,
         * we might want to read from a different device.  So we
         * flag all drives that could conceivably be read from for READ,
         * and any others (which will be non-In_sync devices) for WRITE.
         * If a read fails, we try reading from something else for which READ
         * is OK.
         */

        r1_bio->mddev = mddev;
        r1_bio->sector = sector_nr;
        r1_bio->state = 0;
        set_bit(R1BIO_IsSync, &r1_bio->state);

        for (i=0; i < conf->raid_disks; i++) {
                mdk_rdev_t *rdev;
                bio = r1_bio->bios[i];

                /* take from bio_init */
                bio->bi_next = NULL;
                bio->bi_flags |= 1 << BIO_UPTODATE;
                bio->bi_rw = 0;
                bio->bi_vcnt = 0;
                bio->bi_idx = 0;
                bio->bi_phys_segments = 0;
                bio->bi_hw_segments = 0;
                bio->bi_size = 0;
                bio->bi_end_io = NULL;
                bio->bi_private = NULL;

                rdev = rcu_dereference(conf->mirrors[i].rdev);
                if (rdev == NULL ||
                           test_bit(Faulty, &rdev->flags)) {
                        still_degraded = 1;
                        continue;
                } else if (!test_bit(In_sync, &rdev->flags)) {
                        bio->bi_rw = WRITE;
                        bio->bi_end_io = end_sync_write;
                        write_targets ++;
                } else {
                        /* may need to read from here */
                        bio->bi_rw = READ;
                        bio->bi_end_io = end_sync_read;
                        if (test_bit(WriteMostly, &rdev->flags)) {
                                if (wonly < 0)
                                        wonly = i;
                        } else {
                                if (disk < 0)
                                        disk = i;
                        }
                        read_targets++;
                }
                atomic_inc(&rdev->nr_pending);
                bio->bi_sector = sector_nr + rdev->data_offset;
                bio->bi_bdev = rdev->bdev;
                bio->bi_private = r1_bio;
        }
        rcu_read_unlock();
        if (disk < 0)
                disk = wonly;
        r1_bio->read_disk = disk;

        if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) && read_targets > 0)
                /* extra read targets are also write targets */
                write_targets += read_targets-1;

        if (write_targets == 0 || read_targets == 0) {
                /* There is nowhere to write, so all non-sync
                 * drives must be failed - so we are finished
                 */
                sector_t rv = max_sector - sector_nr;
                *skipped = 1;
                put_buf(r1_bio);
                return rv;
        }

        nr_sectors = 0;
        sync_blocks = 0;
        do {
                struct page *page;
                int len = PAGE_SIZE;
                if (sector_nr + (len>>9) > max_sector)
                        len = (max_sector - sector_nr) << 9;
                if (len == 0)
                        break;
                if (sync_blocks == 0) {
                        if (!bitmap_start_sync(mddev->bitmap, sector_nr,
                                               &sync_blocks, still_degraded) &&
                            !conf->fullsync &&
                            !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery))
                                break;
                        if (sync_blocks < (PAGE_SIZE>>9))
                                BUG();
                        if (len > (sync_blocks<<9))
                                len = sync_blocks<<9;
                }

                for (i=0 ; i < conf->raid_disks; i++) {
                        bio = r1_bio->bios[i];
                        if (bio->bi_end_io) {
                                page = bio->bi_io_vec[bio->bi_vcnt].bv_page;
                                if (bio_add_page(bio, page, len, 0) == 0) {
                                        /* stop here */
                                        bio->bi_io_vec[bio->bi_vcnt].bv_page = page;
                                        while (i > 0) {
                                                i--;
                                                bio = r1_bio->bios[i];
                                                if (bio->bi_end_io==NULL)
                                                        continue;
                                                /* remove last page from this bio */
                                                bio->bi_vcnt--;
                                                bio->bi_size -= len;
                                                bio->bi_flags &= ~(1<< BIO_SEG_VALID);
                                        }
                                        goto bio_full;
                                }
                        }
                }
                nr_sectors += len>>9;
                sector_nr += len>>9;
                sync_blocks -= (len>>9);
        } while (r1_bio->bios[disk]->bi_vcnt < RESYNC_PAGES);
 bio_full:
        r1_bio->sectors = nr_sectors;

        /* For a user-requested sync, we read all readable devices and do a
         * compare
         */
        if (test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery)) {
                atomic_set(&r1_bio->remaining, read_targets);
                for (i=0; i<conf->raid_disks; i++) {
                        bio = r1_bio->bios[i];
                        if (bio->bi_end_io == end_sync_read) {
                                md_sync_acct(conf->mirrors[i].rdev->bdev, nr_sectors);
                                generic_make_request(bio);
                        }
                }
        } else {
                atomic_set(&r1_bio->remaining, 1);
                bio = r1_bio->bios[r1_bio->read_disk];
                md_sync_acct(conf->mirrors[r1_bio->read_disk].rdev->bdev,
                             nr_sectors);
                generic_make_request(bio);

        }

        return nr_sectors;
}

static int run(mddev_t *mddev)
{
        conf_t *conf;
        int i, j, disk_idx;
        mirror_info_t *disk;
        mdk_rdev_t *rdev;
        struct list_head *tmp;

        if (mddev->level != 1) {
                printk("raid1: %s: raid level not set to mirroring (%d)\n",
                       mdname(mddev), mddev->level);
                goto out;
        }
        if (mddev->reshape_position != MaxSector) {
                printk("raid1: %s: reshape_position set but not supported\n",
                       mdname(mddev));
                goto out;
        }
        /*
         * copy the already verified devices into our private RAID1
         * bookkeeping area. [whatever we allocate in run(),
         * should be freed in stop()]
         */
        conf = kzalloc(sizeof(conf_t), GFP_KERNEL);
        mddev->private = conf;
        if (!conf)
                goto out_no_mem;

        conf->mirrors = kzalloc(sizeof(struct mirror_info)*mddev->raid_disks,
                                 GFP_KERNEL);
        if (!conf->mirrors)
                goto out_no_mem;

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

        conf->poolinfo = kmalloc(sizeof(*conf->poolinfo), GFP_KERNEL);
        if (!conf->poolinfo)
                goto out_no_mem;
        conf->poolinfo->mddev = mddev;
        conf->poolinfo->raid_disks = mddev->raid_disks;
        conf->r1bio_pool = mempool_create(NR_RAID1_BIOS, r1bio_pool_alloc,
                                          r1bio_pool_free,
                                          conf->poolinfo);
        if (!conf->r1bio_pool)
                goto out_no_mem;

        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))
                        blk_queue_max_sectors(mddev->queue, 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);
        if (conf->working_disks == 1)
                mddev->recovery_cp = MaxSector;

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

        bio_list_init(&conf->pending_bio_list);
        bio_list_init(&conf->flushing_bio_list);

        if (!conf->working_disks) {
                printk(KERN_ERR "raid1: no 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++;
                }
        }

        /*
         * find the first working one and use it as a starting point
         * to read balancing.
         */
        for (j = 0; j < conf->raid_disks &&
                     (!conf->mirrors[j].rdev ||
                      !test_bit(In_sync, &conf->mirrors[j].rdev->flags)) ; j++)
                /* nothing */;
        conf->last_used = j;


        mddev->thread = md_register_thread(raid1d, mddev, "%s_raid1");
        if (!mddev->thread) {
                printk(KERN_ERR
                       "raid1: couldn't allocate thread for %s\n",
                       mdname(mddev));
                goto out_free_conf;
        }

        printk(KERN_INFO 
                "raid1: raid set %s active with %d out of %d mirrors\n",
                mdname(mddev), mddev->raid_disks - mddev->degraded, 
                mddev->raid_disks);
        /*
         * Ok, everything is just fine now
         */
        mddev->array_size = mddev->size;

        mddev->queue->unplug_fn = raid1_unplug;
        mddev->queue->issue_flush_fn = raid1_issue_flush;

        return 0;

out_no_mem:
        printk(KERN_ERR "raid1: couldn't allocate memory for %s\n",
               mdname(mddev));

out_free_conf:
        if (conf) {
                if (conf->r1bio_pool)
                        mempool_destroy(conf->r1bio_pool);
                kfree(conf->mirrors);
                safe_put_page(conf->tmppage);
                kfree(conf->poolinfo);
                kfree(conf);
                mddev->private = NULL;
        }
out:
        return -EIO;
}

static int stop(mddev_t *mddev)
{
        conf_t *conf = mddev_to_conf(mddev);
        struct bitmap *bitmap = mddev->bitmap;
        int behind_wait = 0;

        /* wait for behind writes to complete */
        while (bitmap && atomic_read(&bitmap->behind_writes) > 0) {
                behind_wait++;
                printk(KERN_INFO "raid1: behind writes in progress on device %s, waiting to stop (%d)\n", mdname(mddev), behind_wait);
                set_current_state(TASK_UNINTERRUPTIBLE);
                schedule_timeout(HZ); /* wait a second */
                /* need to kick something here to make sure I/O goes? */
        }

        md_unregister_thread(mddev->thread);
        mddev->thread = NULL;
        blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
        if (conf->r1bio_pool)
                mempool_destroy(conf->r1bio_pool);
        kfree(conf->mirrors);
        kfree(conf->poolinfo);
        kfree(conf);
        mddev->private = NULL;
        return 0;
}

static int raid1_resize(mddev_t *mddev, sector_t sectors)
{
        /* no resync is happening, and there is enough space
         * on all devices, so we can resize.
         * We need to make sure resync covers any new space.
         * If the array is shrinking we should possibly wait until
         * any io in the removed space completes, but it hardly seems
         * worth it.
         */
        mddev->array_size = sectors>>1;
        set_capacity(mddev->gendisk, mddev->array_size << 1);
        mddev->changed = 1;
        if (mddev->array_size > mddev->size && mddev->recovery_cp == MaxSector) {
                mddev->recovery_cp = mddev->size << 1;
                set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
        }
        mddev->size = mddev->array_size;
        mddev->resync_max_sectors = sectors;
        return 0;
}

static int raid1_reshape(mddev_t *mddev)
{
        /* We need to:
         * 1/ resize the r1bio_pool
         * 2/ resize conf->mirrors
         *
         * We allocate a new r1bio_pool if we can.
         * Then raise a device barrier and wait until all IO stops.
         * Then resize conf->mirrors and swap in the new r1bio pool.
         *
         * At the same time, we "pack" the devices so that all the missing
         * devices have the higher raid_disk numbers.
         */
        mempool_t *newpool, *oldpool;
        struct pool_info *newpoolinfo;
        mirror_info_t *newmirrors;
        conf_t *conf = mddev_to_conf(mddev);
        int cnt, raid_disks;

        int d, d2;

        /* Cannot change chunk_size, layout, or level */
        if (mddev->chunk_size != mddev->new_chunk ||
            mddev->layout != mddev->new_layout ||
            mddev->level != mddev->new_level) {
                mddev->new_chunk = mddev->chunk_size;
                mddev->new_layout = mddev->layout;
                mddev->new_level = mddev->level;
                return -EINVAL;
        }

        raid_disks = mddev->raid_disks + mddev->delta_disks;

        if (raid_disks < conf->raid_disks) {
                cnt=0;
                for (d= 0; d < conf->raid_disks; d++)
                        if (conf->mirrors[d].rdev)
                                cnt++;
                if (cnt > raid_disks)
                        return -EBUSY;
        }

        newpoolinfo = kmalloc(sizeof(*newpoolinfo), GFP_KERNEL);
        if (!newpoolinfo)
                return -ENOMEM;
        newpoolinfo->mddev = mddev;
        newpoolinfo->raid_disks = raid_disks;

        newpool = mempool_create(NR_RAID1_BIOS, r1bio_pool_alloc,
                                 r1bio_pool_free, newpoolinfo);
        if (!newpool) {
                kfree(newpoolinfo);
                return -ENOMEM;
        }
        newmirrors = kzalloc(sizeof(struct mirror_info) * raid_disks, GFP_KERNEL);
        if (!newmirrors) {
                kfree(newpoolinfo);
                mempool_destroy(newpool);
                return -ENOMEM;
        }

        raise_barrier(conf);

        /* ok, everything is stopped */
        oldpool = conf->r1bio_pool;
        conf->r1bio_pool = newpool;

        for (d=d2=0; d < conf->raid_disks; d++)
                if (conf->mirrors[d].rdev) {
                        conf->mirrors[d].rdev->raid_disk = d2;
                        newmirrors[d2++].rdev = conf->mirrors[d].rdev;
                }
        kfree(conf->mirrors);
        conf->mirrors = newmirrors;
        kfree(conf->poolinfo);
        conf->poolinfo = newpoolinfo;

        mddev->degraded += (raid_disks - conf->raid_disks);
        conf->raid_disks = mddev->raid_disks = raid_disks;
        mddev->delta_disks = 0;

        conf->last_used = 0; /* just make sure it is in-range */
        lower_barrier(conf);

        set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
        md_wakeup_thread(mddev->thread);

        mempool_destroy(oldpool);
        return 0;
}

static void raid1_quiesce(mddev_t *mddev, int state)
{
        conf_t *conf = mddev_to_conf(mddev);

        switch(state) {
        case 1:
                raise_barrier(conf);
                break;
        case 0:
                lower_barrier(conf);
                break;
        }
}


static struct mdk_personality raid1_personality =
{
        .name           = "raid1",
        .level          = 1,
        .owner          = THIS_MODULE,
        .make_request   = make_request,
        .run            = run,
        .stop           = stop,
        .status         = status,
        .error_handler  = error,
        .hot_add_disk   = raid1_add_disk,
        .hot_remove_disk= raid1_remove_disk,
        .spare_active   = raid1_spare_active,
        .sync_request   = sync_request,
        .resize         = raid1_resize,
        .check_reshape  = raid1_reshape,
        .quiesce        = raid1_quiesce,
};

static int __init raid_init(void)
{
        return register_md_personality(&raid1_personality);
}

static void raid_exit(void)
{
        unregister_md_personality(&raid1_personality);
}

module_init(raid_init);
module_exit(raid_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS("md-personality-3"); /* RAID1 */
MODULE_ALIAS("md-raid1");
MODULE_ALIAS("md-level-1");