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linear.c

/*
   linear.c : Multiple Devices driver for Linux
            Copyright (C) 1994-96 Marc ZYNGIER
            <zyngier@ufr-info-p7.ibp.fr> or
            <maz@gloups.fdn.fr>

   Linear mode management functions.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.
   
   You should have received a copy of the GNU General Public License
   (for example /usr/src/linux/COPYING); if not, write to the Free
   Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  
*/

#include <linux/module.h>

#include <linux/raid/md.h>
#include <linux/slab.h>
#include <linux/raid/linear.h>

#define MAJOR_NR MD_MAJOR
#define MD_DRIVER
#define MD_PERSONALITY

/*
 * find which device holds a particular offset 
 */
static inline dev_info_t *which_dev(mddev_t *mddev, sector_t sector)
{
      dev_info_t *hash;
      linear_conf_t *conf = mddev_to_conf(mddev);
      sector_t block = sector >> 1;

      /*
       * sector_div(a,b) returns the remainer and sets a to a/b
       */
      block >>= conf->preshift;
      (void)sector_div(block, conf->hash_spacing);
      hash = conf->hash_table[block];

      while ((sector>>1) >= (hash->size + hash->offset))
            hash++;
      return hash;
}

/**
 *    linear_mergeable_bvec -- tell bio layer if 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 take at this offset
 */
static int linear_mergeable_bvec(struct request_queue *q, struct bio *bio, struct bio_vec *biovec)
{
      mddev_t *mddev = q->queuedata;
      dev_info_t *dev0;
      unsigned long maxsectors, bio_sectors = bio->bi_size >> 9;
      sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);

      dev0 = which_dev(mddev, sector);
      maxsectors = (dev0->size << 1) - (sector - (dev0->offset<<1));

      if (maxsectors < bio_sectors)
            maxsectors = 0;
      else
            maxsectors -= bio_sectors;

      if (maxsectors <= (PAGE_SIZE >> 9 ) && bio_sectors == 0)
            return biovec->bv_len;
      /* The bytes available at this offset could be really big,
       * so we cap at 2^31 to avoid overflow */
      if (maxsectors > (1 << (31-9)))
            return 1<<31;
      return maxsectors << 9;
}

static void linear_unplug(struct request_queue *q)
{
      mddev_t *mddev = q->queuedata;
      linear_conf_t *conf = mddev_to_conf(mddev);
      int i;

      for (i=0; i < mddev->raid_disks; i++) {
            struct request_queue *r_queue = bdev_get_queue(conf->disks[i].rdev->bdev);
            blk_unplug(r_queue);
      }
}

static int linear_congested(void *data, int bits)
{
      mddev_t *mddev = data;
      linear_conf_t *conf = mddev_to_conf(mddev);
      int i, ret = 0;

      for (i = 0; i < mddev->raid_disks && !ret ; i++) {
            struct request_queue *q = bdev_get_queue(conf->disks[i].rdev->bdev);
            ret |= bdi_congested(&q->backing_dev_info, bits);
      }
      return ret;
}

static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
{
      linear_conf_t *conf;
      dev_info_t **table;
      mdk_rdev_t *rdev;
      int i, nb_zone, cnt;
      sector_t min_spacing;
      sector_t curr_offset;
      struct list_head *tmp;

      conf = kzalloc (sizeof (*conf) + raid_disks*sizeof(dev_info_t),
                  GFP_KERNEL);
      if (!conf)
            return NULL;

      cnt = 0;
      conf->array_size = 0;

      ITERATE_RDEV(mddev,rdev,tmp) {
            int j = rdev->raid_disk;
            dev_info_t *disk = conf->disks + j;

            if (j < 0 || j > raid_disks || disk->rdev) {
                  printk("linear: disk numbering problem. Aborting!\n");
                  goto out;
            }

            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->size = rdev->size;
            conf->array_size += rdev->size;

            cnt++;
      }
      if (cnt != raid_disks) {
            printk("linear: not enough drives present. Aborting!\n");
            goto out;
      }

      min_spacing = conf->array_size;
      sector_div(min_spacing, PAGE_SIZE/sizeof(struct dev_info *));

      /* min_spacing is the minimum spacing that will fit the hash
       * table in one PAGE.  This may be much smaller than needed.
       * We find the smallest non-terminal set of consecutive devices
       * that is larger than min_spacing as use the size of that as
       * the actual spacing
       */
      conf->hash_spacing = conf->array_size;
      for (i=0; i < cnt-1 ; i++) {
            sector_t sz = 0;
            int j;
            for (j = i; j < cnt - 1 && sz < min_spacing; j++)
                  sz += conf->disks[j].size;
            if (sz >= min_spacing && sz < conf->hash_spacing)
                  conf->hash_spacing = sz;
      }

      /* hash_spacing may be too large for sector_div to work with,
       * so we might need to pre-shift
       */
      conf->preshift = 0;
      if (sizeof(sector_t) > sizeof(u32)) {
            sector_t space = conf->hash_spacing;
            while (space > (sector_t)(~(u32)0)) {
                  space >>= 1;
                  conf->preshift++;
            }
      }
      /*
       * This code was restructured to work around a gcc-2.95.3 internal
       * compiler error.  Alter it with care.
       */
      {
            sector_t sz;
            unsigned round;
            unsigned long base;

            sz = conf->array_size >> conf->preshift;
            sz += 1; /* force round-up */
            base = conf->hash_spacing >> conf->preshift;
            round = sector_div(sz, base);
            nb_zone = sz + (round ? 1 : 0);
      }
      BUG_ON(nb_zone > PAGE_SIZE / sizeof(struct dev_info *));

      conf->hash_table = kmalloc (sizeof (struct dev_info *) * nb_zone,
                              GFP_KERNEL);
      if (!conf->hash_table)
            goto out;

      /*
       * Here we generate the linear hash table
       * First calculate the device offsets.
       */
      conf->disks[0].offset = 0;
      for (i = 1; i < raid_disks; i++)
            conf->disks[i].offset =
                  conf->disks[i-1].offset +
                  conf->disks[i-1].size;

      table = conf->hash_table;
      curr_offset = 0;
      i = 0;
      for (curr_offset = 0;
           curr_offset < conf->array_size;
           curr_offset += conf->hash_spacing) {

            while (i < raid_disks-1 &&
                   curr_offset >= conf->disks[i+1].offset)
                  i++;

            *table ++ = conf->disks + i;
      }

      if (conf->preshift) {
            conf->hash_spacing >>= conf->preshift;
            /* round hash_spacing up so that when we divide by it,
             * we err on the side of "too-low", which is safest.
             */
            conf->hash_spacing++;
      }

      BUG_ON(table - conf->hash_table > nb_zone);

      return conf;

out:
      kfree(conf);
      return NULL;
}

static int linear_run (mddev_t *mddev)
{
      linear_conf_t *conf;

      conf = linear_conf(mddev, mddev->raid_disks);

      if (!conf)
            return 1;
      mddev->private = conf;
      mddev->array_size = conf->array_size;

      blk_queue_merge_bvec(mddev->queue, linear_mergeable_bvec);
      mddev->queue->unplug_fn = linear_unplug;
      mddev->queue->backing_dev_info.congested_fn = linear_congested;
      mddev->queue->backing_dev_info.congested_data = mddev;
      return 0;
}

static int linear_add(mddev_t *mddev, mdk_rdev_t *rdev)
{
      /* Adding a drive to a linear array allows the array to grow.
       * It is permitted if the new drive has a matching superblock
       * already on it, with raid_disk equal to raid_disks.
       * It is achieved by creating a new linear_private_data structure
       * and swapping it in in-place of the current one.
       * The current one is never freed until the array is stopped.
       * This avoids races.
       */
      linear_conf_t *newconf;

      if (rdev->saved_raid_disk != mddev->raid_disks)
            return -EINVAL;

      rdev->raid_disk = rdev->saved_raid_disk;

      newconf = linear_conf(mddev,mddev->raid_disks+1);

      if (!newconf)
            return -ENOMEM;

      newconf->prev = mddev_to_conf(mddev);
      mddev->private = newconf;
      mddev->raid_disks++;
      mddev->array_size = newconf->array_size;
      set_capacity(mddev->gendisk, mddev->array_size << 1);
      return 0;
}

static int linear_stop (mddev_t *mddev)
{
      linear_conf_t *conf = mddev_to_conf(mddev);
  
      blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
      do {
            linear_conf_t *t = conf->prev;
            kfree(conf->hash_table);
            kfree(conf);
            conf = t;
      } while (conf);

      return 0;
}

static int linear_make_request (struct request_queue *q, struct bio *bio)
{
      const int rw = bio_data_dir(bio);
      mddev_t *mddev = q->queuedata;
      dev_info_t *tmp_dev;
      sector_t block;

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

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

      tmp_dev = which_dev(mddev, bio->bi_sector);
      block = bio->bi_sector >> 1;
    
      if (unlikely(block >= (tmp_dev->size + tmp_dev->offset)
                 || block < tmp_dev->offset)) {
            char b[BDEVNAME_SIZE];

            printk("linear_make_request: Block %llu out of bounds on "
                  "dev %s size %llu offset %llu\n",
                  (unsigned long long)block,
                  bdevname(tmp_dev->rdev->bdev, b),
                  (unsigned long long)tmp_dev->size,
                    (unsigned long long)tmp_dev->offset);
            bio_io_error(bio);
            return 0;
      }
      if (unlikely(bio->bi_sector + (bio->bi_size >> 9) >
                 (tmp_dev->offset + tmp_dev->size)<<1)) {
            /* This bio crosses a device boundary, so we have to
             * split it.
             */
            struct bio_pair *bp;
            bp = bio_split(bio, bio_split_pool,
                         ((tmp_dev->offset + tmp_dev->size)<<1) - bio->bi_sector);
            if (linear_make_request(q, &bp->bio1))
                  generic_make_request(&bp->bio1);
            if (linear_make_request(q, &bp->bio2))
                  generic_make_request(&bp->bio2);
            bio_pair_release(bp);
            return 0;
      }
                
      bio->bi_bdev = tmp_dev->rdev->bdev;
      bio->bi_sector = bio->bi_sector - (tmp_dev->offset << 1) + tmp_dev->rdev->data_offset;

      return 1;
}

static void linear_status (struct seq_file *seq, mddev_t *mddev)
{

#undef MD_DEBUG
#ifdef MD_DEBUG
      int j;
      linear_conf_t *conf = mddev_to_conf(mddev);
      sector_t s = 0;
  
      seq_printf(seq, "      ");
      for (j = 0; j < mddev->raid_disks; j++)
      {
            char b[BDEVNAME_SIZE];
            s += conf->smallest_size;
            seq_printf(seq, "[%s",
                     bdevname(conf->hash_table[j][0].rdev->bdev,b));

            while (s > conf->hash_table[j][0].offset +
                       conf->hash_table[j][0].size)
                  seq_printf(seq, "/%s] ",
                           bdevname(conf->hash_table[j][1].rdev->bdev,b));
            else
                  seq_printf(seq, "] ");
      }
      seq_printf(seq, "\n");
#endif
      seq_printf(seq, " %dk rounding", mddev->chunk_size/1024);
}


static struct mdk_personality linear_personality =
{
      .name       = "linear",
      .level            = LEVEL_LINEAR,
      .owner            = THIS_MODULE,
      .make_request     = linear_make_request,
      .run        = linear_run,
      .stop       = linear_stop,
      .status           = linear_status,
      .hot_add_disk     = linear_add,
};

static int __init linear_init (void)
{
      return register_md_personality (&linear_personality);
}

static void linear_exit (void)
{
      unregister_md_personality (&linear_personality);
}


module_init(linear_init);
module_exit(linear_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS("md-personality-1"); /* LINEAR - deprecated*/
MODULE_ALIAS("md-linear");
MODULE_ALIAS("md-level--1");

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