1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 04e5fd742c2c..ebaaf72cd822 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -38,6 +38,8 @@ struct dm_table {
         sector_t *highs;
         struct dm_target *targets;
 
+        unsigned barriers_supported:1;
+
         /*
          * Indicates the rw permissions for the new logical
          * device.  This should be a combination of FMODE_READ
@@ -227,6 +229,7 @@ int dm_table_create(struct dm_table **result, fmode_t mode,
 
         INIT_LIST_HEAD(&t->devices);
         atomic_set(&t->holders, 1);
+        t->barriers_supported = 1;
 
         if (!num_targets)
                 num_targets = KEYS_PER_NODE;
@@ -728,6 +731,10 @@ int dm_table_add_target(struct dm_table *t, const char *type,
         /* FIXME: the plan is to combine high here and then have
          * the merge fn apply the target level restrictions. */
         combine_restrictions_low(&t->limits, &tgt->limits);
+
+        if (!(tgt->type->features & DM_TARGET_SUPPORTS_BARRIERS))
+                t->barriers_supported = 0;
+
         return 0;
 
  bad:
@@ -772,6 +779,12 @@ int dm_table_complete(struct dm_table *t)
 
         check_for_valid_limits(&t->limits);
 
+        /*
+         * We only support barriers if there is exactly one underlying device.
+         */
+        if (!list_is_singular(&t->devices))
+                t->barriers_supported = 0;
+
         /* how many indexes will the btree have ? */
         leaf_nodes = dm_div_up(t->num_targets, KEYS_PER_NODE);
         t->depth = 1 + int_log(leaf_nodes, CHILDREN_PER_NODE);
@@ -986,6 +999,12 @@ struct mapped_device *dm_table_get_md(struct dm_table *t)
         return t->md;
 }
 
+int dm_table_barrier_ok(struct dm_table *t)
+{
+        return t->barriers_supported;
+}
+EXPORT_SYMBOL(dm_table_barrier_ok);
+
 EXPORT_SYMBOL(dm_vcalloc);
 EXPORT_SYMBOL(dm_get_device);
 EXPORT_SYMBOL(dm_put_device);