dm stripe: support discards

The DM core will submit a discard bio to the stripe target for each
stripe in a striped DM device.  The stripe target will determine
stripe-specific portions of the supplied bio to be remapped into
individual (at most 'num_discard_requests' extents).  If a given
stripe-specific discard bio doesn't touch a particular stripe the bio
will be dropped.

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

1 files changed, 39 insertions, 0 deletions

diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
index 1559fdfd2073..c297f6da91ea 100644
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -176,6 +176,7 @@ static int stripe_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
         ti->split_io = chunk_size;
         ti->num_flush_requests = stripes;
+        ti->num_discard_requests = stripes;
 
         sc->chunk_shift = ffs(chunk_size) - 1;
         sc->chunk_mask = ((sector_t) chunk_size) - 1;
@@ -230,6 +231,39 @@ static void stripe_map_sector(struct stripe_c *sc, sector_t sector,
         *result = (chunk << sc->chunk_shift) | (offset & sc->chunk_mask);
 }
 
+static void stripe_map_range_sector(struct stripe_c *sc, sector_t sector,
+                                    uint32_t target_stripe, sector_t *result)
+{
+        uint32_t stripe;
+
+        stripe_map_sector(sc, sector, &stripe, result);
+        if (stripe == target_stripe)
+                return;
+        *result &= ~sc->chunk_mask;                     /* round down */
+        if (target_stripe < stripe)
+                *result += sc->chunk_mask + 1;          /* next chunk */
+}
+
+static int stripe_map_discard(struct stripe_c *sc, struct bio *bio,
+                              uint32_t target_stripe)
+{
+        sector_t begin, end;
+
+        stripe_map_range_sector(sc, bio->bi_sector, target_stripe, &begin);
+        stripe_map_range_sector(sc, bio->bi_sector + bio_sectors(bio),
+                                target_stripe, &end);
+        if (begin < end) {
+                bio->bi_bdev = sc->stripe[target_stripe].dev->bdev;
+                bio->bi_sector = begin + sc->stripe[target_stripe].physical_start;
+                bio->bi_size = to_bytes(end - begin);
+                return DM_MAPIO_REMAPPED;
+        } else {
+                /* The range doesn't map to the target stripe */
+                bio_endio(bio, 0);
+                return DM_MAPIO_SUBMITTED;
+        }
+}
+
 static int stripe_map(struct dm_target *ti, struct bio *bio,
                       union map_info *map_context)
 {
@@ -243,6 +277,11 @@ static int stripe_map(struct dm_target *ti, struct bio *bio,
                 bio->bi_bdev = sc->stripe[target_request_nr].dev->bdev;
                 return DM_MAPIO_REMAPPED;
         }
+        if (unlikely(bio->bi_rw & REQ_DISCARD)) {
+                target_request_nr = map_context->target_request_nr;
+                BUG_ON(target_request_nr >= sc->stripes);
+                return stripe_map_discard(sc, bio, target_request_nr);
+        }
 
         stripe_map_sector(sc, bio->bi_sector, &stripe, &bio->bi_sector);