dm: introduce merge_bvec_fn

[karo-tx-linux.git] / drivers / md / dm.c

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index efe9690749282d3cc3ae19a2139c2b81e9ce61f7..bca448e118786a78a5e07b54f3cb3a7e3aca85d5 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -829,6 +829,49 @@ static int __split_bio(struct mapped_device *md, struct bio *bio)
  * CRUD END
  *---------------------------------------------------------------*/
 
+static int dm_merge_bvec(struct request_queue *q,
+                        struct bvec_merge_data *bvm,
+                        struct bio_vec *biovec)
+{
+       struct mapped_device *md = q->queuedata;
+       struct dm_table *map = dm_get_table(md);
+       struct dm_target *ti;
+       sector_t max_sectors;
+       int max_size;
+
+       if (unlikely(!map))
+               return 0;
+
+       ti = dm_table_find_target(map, bvm->bi_sector);
+
+       /*
+        * Find maximum amount of I/O that won't need splitting
+        */
+       max_sectors = min(max_io_len(md, bvm->bi_sector, ti),
+                         (sector_t) BIO_MAX_SECTORS);
+       max_size = (max_sectors << SECTOR_SHIFT) - bvm->bi_size;
+       if (max_size < 0)
+               max_size = 0;
+
+       /*
+        * merge_bvec_fn() returns number of bytes
+        * it can accept at this offset
+        * max is precomputed maximal io size
+        */
+       if (max_size && ti->type->merge)
+               max_size = ti->type->merge(ti, bvm, biovec, max_size);
+
+       /*
+        * Always allow an entire first page
+        */
+       if (max_size <= biovec->bv_len && !(bvm->bi_size >> SECTOR_SHIFT))
+               max_size = biovec->bv_len;
+
+       dm_table_put(map);
+
+       return max_size;
+}
+
 /*
  * The request function that just remaps the bio built up by
  * dm_merge_bvec.
@@ -1032,6 +1075,7 @@ static struct mapped_device *alloc_dev(int minor)
        blk_queue_make_request(md->queue, dm_request);
        blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
        md->queue->unplug_fn = dm_unplug_all;
+       blk_queue_merge_bvec(md->queue, dm_merge_bvec);
 
        md->io_pool = mempool_create_slab_pool(MIN_IOS, _io_cache);
        if (!md->io_pool)