dm zero: add discard support

Add zero_io_hints() and set discard limits so that the zero target
advertises support for discards.

The zero target will ignore discards.

This is useful when the user combines dm-zero with other
discard-supporting targets in the same table; without dm-zero support,
discards would be disabled for the whole combined device.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Tested-by: Milan Broz <gmazyland@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-zero.c b/drivers/md/dm-zero.c
index 2601cd5..6215d8e 100644 (file)
--- a/drivers/md/dm-zero.c
+++ b/drivers/md/dm-zero.c
@@ -27,6 +27,7 @@ static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
         * Silently drop discards, avoiding -EOPNOTSUPP.
         */
        ti->num_discard_bios = 1;
+       ti->discards_supported = true;
 
        return 0;
 }
@@ -45,6 +46,7 @@ static int zero_map(struct dm_target *ti, struct bio *bio)
                zero_fill_bio(bio);
                break;
        case REQ_OP_WRITE:
+       case REQ_OP_DISCARD:
                /* writes get silently dropped */
                break;
        default:
@@ -57,13 +59,21 @@ static int zero_map(struct dm_target *ti, struct bio *bio)
        return DM_MAPIO_SUBMITTED;
 }
 
+static void zero_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+       limits->max_discard_sectors = UINT_MAX;
+       limits->max_hw_discard_sectors = UINT_MAX;
+       limits->discard_granularity = 512;
+}
+
 static struct target_type zero_target = {
        .name   = "zero",
-       .version = {1, 1, 0},
+       .version = {1, 2, 0},
        .features = DM_TARGET_NOWAIT,
        .module = THIS_MODULE,
        .ctr    = zero_ctr,
        .map    = zero_map,
+       .io_hints = zero_io_hints,
 };
 
 static int __init dm_zero_init(void)