dm thin: implement thin_merge

Introduce thin_merge so that any additional constraints from the data
volume may be taken into account when determing the maximum number of
sectors that can be issued relative to the specified logical offset.

This is particularly important if/when the data volume is layered ontop
of a more sophisticated device (e.g. dm-raid or some other DM target).

Reviewed-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index de55ae9d4926eb8c650b72b6c9e243fce98de400..0686078286914183d3eba95d8bc8d22f2aa6bc1a 100644 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3307,7 +3307,7 @@ static struct target_type pool_target = {
        .name = "thin-pool",
        .features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
                    DM_TARGET_IMMUTABLE,
-       .version = {1, 13, 0},
+       .version = {1, 14, 0},
        .module = THIS_MODULE,
        .ctr = pool_ctr,
        .dtr = pool_dtr,
@@ -3634,6 +3634,21 @@ err:
        DMEMIT("Error");
 }
 
+static int thin_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
+                     struct bio_vec *biovec, int max_size)
+{
+       struct thin_c *tc = ti->private;
+       struct request_queue *q = bdev_get_queue(tc->pool_dev->bdev);
+
+       if (!q->merge_bvec_fn)
+               return max_size;
+
+       bvm->bi_bdev = tc->pool_dev->bdev;
+       bvm->bi_sector = dm_target_offset(ti, bvm->bi_sector);
+
+       return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
+}
+
 static int thin_iterate_devices(struct dm_target *ti,
                                iterate_devices_callout_fn fn, void *data)
 {
@@ -3658,7 +3673,7 @@ static int thin_iterate_devices(struct dm_target *ti,
 
 static struct target_type thin_target = {
        .name = "thin",
-       .version = {1, 13, 0},
+       .version = {1, 14, 0},
        .module = THIS_MODULE,
        .ctr = thin_ctr,
        .dtr = thin_dtr,
@@ -3668,6 +3683,7 @@ static struct target_type thin_target = {
        .presuspend = thin_presuspend,
        .postsuspend = thin_postsuspend,
        .status = thin_status,
+       .merge = thin_merge,
        .iterate_devices = thin_iterate_devices,
 };