dm: add WRITE SAME support

WRITE SAME bios have a payload that contain a single page.  When
cloning WRITE SAME bios DM has no need to modify the bi_io_vec
attributes (and doing so would be detrimental).  DM need only alter the
start and end of the WRITE SAME bio accordingly.

Rather than duplicate __clone_and_map_discard, factor out a common
function that is also used by __clone_and_map_write_same.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 77e6eff..5401cdc 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1174,7 +1174,28 @@ static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti)
        ci->sector_count = 0;
 }
 
-static int __clone_and_map_discard(struct clone_info *ci)
+typedef unsigned (*get_num_requests_fn)(struct dm_target *ti);
+
+static unsigned get_num_discard_requests(struct dm_target *ti)
+{
+       return ti->num_discard_requests;
+}
+
+static unsigned get_num_write_same_requests(struct dm_target *ti)
+{
+       return ti->num_write_same_requests;
+}
+
+typedef bool (*is_split_required_fn)(struct dm_target *ti);
+
+static bool is_split_required_for_discard(struct dm_target *ti)
+{
+       return ti->split_discard_requests;
+}
+
+static int __clone_and_map_changing_extent_only(struct clone_info *ci,
+                                               get_num_requests_fn get_num_requests,
+                                               is_split_required_fn is_split_required)
 {
        struct dm_target *ti;
        sector_t len;
@@ -1185,15 +1206,15 @@ static int __clone_and_map_discard(struct clone_info *ci)
                        return -EIO;
 
                /*
-                * Even though the device advertised discard support,
-                * that does not mean every target supports it, and
+                * Even though the device advertised support for this type of
+                * request, that does not mean every target supports it, and
                 * reconfiguration might also have changed that since the
                 * check was performed.
                 */
-               if (!ti->num_discard_requests)
+               if (!get_num_requests || !get_num_requests(ti))
                        return -EOPNOTSUPP;
 
-               if (!ti->split_discard_requests)
+               if (is_split_required && !is_split_required(ti))
                        len = min(ci->sector_count, max_io_len_target_boundary(ci->sector, ti));
                else
                        len = min(ci->sector_count, max_io_len(ci->sector, ti));
@@ -1206,6 +1227,17 @@ static int __clone_and_map_discard(struct clone_info *ci)
        return 0;
 }
 
+static int __clone_and_map_discard(struct clone_info *ci)
+{
+       return __clone_and_map_changing_extent_only(ci, get_num_discard_requests,
+                                                   is_split_required_for_discard);
+}
+
+static int __clone_and_map_write_same(struct clone_info *ci)
+{
+       return __clone_and_map_changing_extent_only(ci, get_num_write_same_requests, NULL);
+}
+
 static int __clone_and_map(struct clone_info *ci)
 {
        struct bio *bio = ci->bio;
@@ -1215,6 +1247,8 @@ static int __clone_and_map(struct clone_info *ci)
 
        if (unlikely(bio->bi_rw & REQ_DISCARD))
                return __clone_and_map_discard(ci);
+       else if (unlikely(bio->bi_rw & REQ_WRITE_SAME))
+               return __clone_and_map_write_same(ci);
 
        ti = dm_table_find_target(ci->map, ci->sector);
        if (!dm_target_is_valid(ti))