5 files changed, 33 insertions, 10 deletions

diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index 79fb53e51c70..bfa107f59d96 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -142,6 +142,7 @@ static struct target_type linear_target = {
         .status = linear_status,
         .ioctl  = linear_ioctl,
         .merge  = linear_merge,
+        .features = DM_TARGET_SUPPORTS_BARRIERS,
 };
 
 int __init dm_linear_init(void)
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);
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4882ce7e88a3..dd953b189f45 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -835,7 +835,11 @@ static int __split_bio(struct mapped_device *md, struct bio *bio)
         ci.map = dm_get_table(md);
         if (unlikely(!ci.map))
                 return -EIO;
-
+        if (unlikely(bio_barrier(bio) && !dm_table_barrier_ok(ci.map))) {
+                dm_table_put(ci.map);
+                bio_endio(bio, -EOPNOTSUPP);
+                return 0;
+        }
         ci.md = md;
         ci.bio = bio;
         ci.io = alloc_io(md);
@@ -919,15 +923,6 @@ static int dm_request(struct request_queue *q, struct bio *bio)
         struct mapped_device *md = q->queuedata;
         int cpu;
 
-        /*
-         * There is no use in forwarding any barrier request since we can't
-         * guarantee it is (or can be) handled by the targets correctly.
-         */
-        if (unlikely(bio_barrier(bio))) {
-                bio_endio(bio, -EOPNOTSUPP);
-                return 0;
-        }
-
         down_read(&md->io_lock);
 
         cpu = part_stat_lock();
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 0ade60cdef42..5b5d08ba9e92 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -51,6 +51,7 @@ int dm_table_any_congested(struct dm_table *t, int bdi_bits);
  * To check the return value from dm_table_find_target().
  */
 #define dm_target_is_valid(t) ((t)->table)
+int dm_table_barrier_ok(struct dm_table *t);
 
 /*-----------------------------------------------------------------
  * A registry of target types.
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index c1ba76c7c0e5..8209e08969f9 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -112,7 +112,14 @@ void dm_put_device(struct dm_target *ti, struct dm_dev *d);
 /*
  * Information about a target type
  */
+
+/*
+ * Target features
+ */
+#define DM_TARGET_SUPPORTS_BARRIERS 0x00000001
+
 struct target_type {
+        uint64_t features;
         const char *name;
         struct module *module;
         unsigned version[3];