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raid10.c

/*
 * raid10.c : Multiple Devices driver for Linux
 *
 * Copyright (C) 2000-2004 Neil Brown
 *
 * RAID-10 support for md.
 *
 * Base on code in raid1.c.  See raid1.c for futher copyright information.
 *
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include "dm-bio-list.h"
#include <linux/raid/raid10.h>
#include <linux/raid/bitmap.h>

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

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

static void unplug_slaves(mddev_t *mddev);

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

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

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

      return r10_bio;
}

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

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

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

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

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

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

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

      return r10_bio;

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

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

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

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

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

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

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

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

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

      mempool_free(r10_bio, conf->r10buf_pool);

      lower_barrier(conf);
}

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

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

      md_wakeup_thread(mddev->thread);
}

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

      bio_endio(bio, 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:
       */
      update_head_pos(slot, r10_bio);

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

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

      update_head_pos(slot, r10_bio);

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

      rdev_dec_pending(conf->mirrors[dev].rdev, conf->mddev);
      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.
 *
 * raid10_find_virt does the reverse mapping, from a device and a
 * sector offset to a virtual address
 */

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

      int slot = 0;

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

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

      sector += stripe << conf->chunk_shift;

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

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

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

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

/**
 *    raid10_mergeable_bvec -- tell bio layer if a two requests can be merged
 *    @q: request queue
 *    @bio: the buffer head that's been built up so far
 *    @biovec: the request that could be merged to it.
 *
 *    Return amount of bytes we can accept at this offset
 *      If near_copies == raid_disk, there are no striping issues,
 *      but in that case, the function isn't called at all.
 */
static int raid10_mergeable_bvec(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 (recovery is ok), or below
       * the resync window. We take the first readable disk when
       * above the resync window.
       */
      if (conf->mddev->recovery_cp < MaxSector
          && (this_sector + sectors >= conf->next_resync)) {
            /* make sure that disk is operational */
            slot = 0;
            disk = r10_bio->devs[slot].devnum;

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


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


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

      /* Find the disk whose head is closest */

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


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

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

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

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

      return disk;
}

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

      rcu_read_lock();
      for (i=0; i<mddev->raid_disks; i++) {
            mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[i].rdev);
            if (rdev && !test_bit(Faulty, &rdev->flags) && atomic_read(&rdev->nr_pending)) {
                  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)
{
      mddev_t *mddev = q->queuedata;

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

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;
}

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

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

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

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

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

      spin_unlock_irq(&conf->resync_lock);
}

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

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

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

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

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

static int make_request(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);
      struct bio_list bl;
      unsigned long flags;

      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.
       */
      wait_barrier(conf);

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

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

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

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

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

            read_bio = bio_clone(bio, GFP_NOIO);

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

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

            generic_make_request(read_bio);
            return 0;
      }

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

      atomic_set(&r10_bio->remaining, 0);

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

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

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

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

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

      return 0;
}

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

      if (conf->near_copies < conf->raid_disks)
            seq_printf(seq, " %dK chunks", mddev->chunk_size/1024);
      if (conf->near_copies > 1)
            seq_printf(seq, " %d near-copies", conf->near_copies);
      if (conf->far_copies > 1) {
            if (conf->far_offset)
                  seq_printf(seq, " %d offset-copies", conf->far_copies);
            else
                  seq_printf(seq, " %d far-copies", conf->far_copies);
      }
      seq_printf(seq, " [%d/%d] [", conf->raid_disks,
                                    conf->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)
{
      wait_barrier(conf);
      allow_barrier(conf);

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

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

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

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

      /*
       * Find all non-in_sync disks within the RAID10 configuration
       * and mark them in_sync
       */
      for (i = 0; i < conf->raid_disks; i++) {
            tmp = conf->mirrors + i;
            if (tmp->rdev
                && !test_bit(Faulty, &tmp->rdev->flags)
                && !test_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;

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

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

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

      print_conf(conf);
      return found;
}

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

      print_conf(conf);
      rdev = p->rdev;
      if (rdev) {
            if (test_bit(In_sync, &rdev->flags) ||
                atomic_read(&rdev->nr_pending)) {
                  err = -EBUSY;
                  goto abort;
            }
            p->rdev = NULL;
            synchronize_rcu();
            if (atomic_read(&rdev->nr_pending)) {
                  /* lost the race, try later */
                  err = -EBUSY;
                  p->rdev = rdev;
            }
      }
abort:

      print_conf(conf);
      return err;
}


static int end_sync_read(struct bio *bio, unsigned int bytes_done, int error)
{
      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;
      BUG_ON(i == conf->copies);
      update_head_pos(i, r10_bio);
      d = r10_bio->devs[i].devnum;

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

      /* for reconstruct, we always reschedule after a read.
       * for resync, only after all reads
       */
      if (test_bit(R10BIO_IsRecover, &r10_bio->state) ||
          atomic_dec_and_test(&r10_bio->remaining)) {
            /* we have read all the blocks,
             * do the comparison in process context in raid10d
             */
            reschedule_retry(r10_bio);
      }
      rdev_dec_pending(conf->mirrors[d].rdev, conf->mddev);
      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=0 ; i < conf->copies ; i++) {
            int  j, d;
            int vcnt = r10_bio->sectors >> (PAGE_SHIFT-9);

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

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

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

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

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

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

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

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

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


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

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


/*
 * This is a kernel thread which:
 *
 *    1.    Retries failed read operations on working mirrors.
 *    2.    Updates the raid superblock when problems encounter.
 *    3.    Performs writes following reads for array 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 (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;
            r10_bio = list_entry(head->prev, r10bio_t, retry_list);
            list_del(head->prev);
            conf->nr_queued--;
            spin_unlock_irqrestore(&conf->device_lock, flags);

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

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

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

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

                                          rdev_dec_pending(rdev, mddev);
                                          rcu_read_lock();
                                    }
                              }
                              rcu_read_unlock();
                        } else {
                              /* Cannot read from anywhere -- bye bye array */
                              md_error(mddev, conf->mirrors[r10_bio->devs[r10_bio->read_slot].devnum].rdev);
                              break;
                        }
                        sectors -= s;
                        sect += s;
                  }

                  unfreeze_array(conf);

                  bio = r10_bio->devs[r10_bio->read_slot].bio;
                  r10_bio->devs[r10_bio->read_slot].bio =
                        mddev->ro ? IO_BLOCKED : NULL;
                  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;
      BUG_ON(conf->r10buf_pool);
      conf->r10buf_pool = mempool_create(buffs, r10buf_pool_alloc, r10buf_pool_free, conf);
      if (!conf->r10buf_pool)
            return -ENOMEM;
      conf->next_resync = 0;
      return 0;
}

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

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

      sector_t sectors_skipped = 0;
      int chunks_skipped = 0;

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

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

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

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

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

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

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

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

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

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

                        for (j=0; j<conf->copies;j++) {
                              int d = r10_bio->devs[j].devnum;
                              if (conf->mirrors[d].rdev &&
                                  test_bit(In_sync, &conf->mirrors[d].rdev->flags)) {
                                    /* This is where we read from */
                                    bio = r10_bio->devs[0].bio;
                                    bio->bi_next = biolist;
                                    biolist = bio;
                                    bio->bi_private = r10_bio;
                                    bio->bi_end_io = end_sync_read;
                                    bio->bi_rw = 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;

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

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

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

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

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

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

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

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

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

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

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

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

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

      conf->near_copies = nc;
      conf->far_copies = fc;
      conf->copies = nc*fc;
      conf->far_offset = fo;
      conf->chunk_mask = (sector_t)(mddev->chunk_size>>9)-1;
      conf->chunk_shift = ffz(~mddev->chunk_size) - 9;
      if (fo)
            conf->stride = 1 << conf->chunk_shift;
      else {
            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_barrier);

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

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

            disk = conf->mirrors + i;

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


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

      printk(KERN_INFO
            "raid10: raid set %s active with %d out of %d devices\n",
            mdname(mddev), mddev->raid_disks - mddev->degraded,
            mddev->raid_disks);
      /*
       * Ok, everything is just fine now
       */
      if (conf->far_offset) {
            size = mddev->size >> (conf->chunk_shift-1);
            size *= conf->raid_disks;
            size <<= conf->chunk_shift;
            sector_div(size, conf->far_copies);
      } else
            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_SIZE);
            stripe /= conf->near_copies;
            if (mddev->queue->backing_dev_info.ra_pages < 2* stripe)
                  mddev->queue->backing_dev_info.ra_pages = 2* stripe;
      }

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

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

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

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

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

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

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

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

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

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

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