1 files changed, 44 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index bc60ef77a0d8..f9fc07d7a4b9 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -54,6 +54,8 @@ struct dm_table {
         sector_t *highs;
         struct dm_target *targets;
 
+        unsigned discards_supported:1;
+
         /*
          * Indicates the rw permissions for the new logical
          * device.  This should be a combination of FMODE_READ
@@ -203,6 +205,7 @@ int dm_table_create(struct dm_table **result, fmode_t mode,
 
         INIT_LIST_HEAD(&t->devices);
         atomic_set(&t->holders, 0);
+        t->discards_supported = 1;
 
         if (!num_targets)
                 num_targets = KEYS_PER_NODE;
@@ -770,6 +773,9 @@ int dm_table_add_target(struct dm_table *t, const char *type,
 
         t->highs[t->num_targets++] = tgt->begin + tgt->len - 1;
 
+        if (!tgt->num_discard_requests)
+                t->discards_supported = 0;
+
         return 0;
 
  bad:
@@ -1135,6 +1141,11 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
         else
                 queue_flag_set_unlocked(QUEUE_FLAG_CLUSTER, q);
 
+        if (!dm_table_supports_discards(t))
+                queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, q);
+        else
+                queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
+
         dm_table_set_integrity(t);
 
         /*
@@ -1281,6 +1292,39 @@ struct mapped_device *dm_table_get_md(struct dm_table *t)
         return t->md;
 }
 
+static int device_discard_capable(struct dm_target *ti, struct dm_dev *dev,
+                                  sector_t start, sector_t len, void *data)
+{
+        struct request_queue *q = bdev_get_queue(dev->bdev);
+
+        return q && blk_queue_discard(q);
+}
+
+bool dm_table_supports_discards(struct dm_table *t)
+{
+        struct dm_target *ti;
+        unsigned i = 0;
+
+        if (!t->discards_supported)
+                return 0;
+
+        /*
+         * Ensure that at least one underlying device supports 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.
+         */
+        while (i < dm_table_get_num_targets(t)) {
+                ti = dm_table_get_target(t, i++);
+
+                if (ti->type->iterate_devices &&
+                    ti->type->iterate_devices(ti, device_discard_capable, NULL))
+                        return 1;
+        }
+
+        return 0;
+}
+
 EXPORT_SYMBOL(dm_vcalloc);
 EXPORT_SYMBOL(dm_get_device);
 EXPORT_SYMBOL(dm_put_device);