dm table: allow targets to support discards internally

Permit a target to support discards regardless of whether or not all its
underlying devices do.

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

2 files changed, 11 insertions, 1 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index cb8380c9767f..215e112d153e 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1346,7 +1346,8 @@ bool dm_table_supports_discards(struct dm_table *t)
                 return 0;
 
         /*
-         * Ensure that at least one underlying device supports discards.
+         * Unless any target used by the table set discards_supported,
+         * require at least one underlying device to support discards.
          * t->devices includes internal dm devices such as mirror logs
          * so we need to use iterate_devices here, which targets
          * supporting discard must provide.
@@ -1354,6 +1355,9 @@ bool dm_table_supports_discards(struct dm_table *t)
         while (i < dm_table_get_num_targets(t)) {
                 ti = dm_table_get_target(t, i++);
 
+                if (ti->discards_supported)
+                        return 1;
+
                 if (ti->type->iterate_devices &&
                     ti->type->iterate_devices(ti, device_discard_capable, NULL))
                         return 1;
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 32a4423710f5..4427e0454051 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -191,6 +191,12 @@ struct dm_target {
 
         /* Used to provide an error string from the ctr */
         char *error;
+
+        /*
+         * Set if this target needs to receive discards regardless of
+         * whether or not its underlying devices have support.
+         */
+        unsigned discards_supported:1;
 };
 
 /* Each target can link one of these into the table */