dm: remove limited barrier support

Prepare for full barrier implementation: first remove the restricted support.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-linear.c

@@ -142,7 +142,6 @@ 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)

drivers/md/dm-table.c

@@ -52,8 +52,6 @@ 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
@@ -243,7 +241,6 @@ int dm_table_create(struct dm_table **result, fmode_t mode,
 
 	INIT_LIST_HEAD(&t->devices);
 	atomic_set(&t->holders, 0);
-	t->barriers_supported = 1;
 
 	if (!num_targets)
 		num_targets = KEYS_PER_NODE;
@@ -751,10 +748,6 @@ 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:
@@ -799,12 +792,6 @@ 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);
@@ -1059,12 +1046,6 @@ 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);

drivers/md/dm.c

@@ -851,11 +851,7 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
 		bio_io_error(bio);
 		return;
 	}
-	if (unlikely(bio_barrier(bio) && !dm_table_barrier_ok(ci.map))) {
-		dm_table_put(ci.map);
-		bio_endio(bio, -EOPNOTSUPP);
-		return;
-	}
+
 	ci.md = md;
 	ci.bio = bio;
 	ci.io = alloc_io(md);
@@ -937,6 +933,15 @@ 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();

drivers/md/dm.h

@@ -52,7 +52,6 @@ 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.

include/linux/device-mapper.h

@@ -116,7 +116,6 @@ void dm_put_device(struct dm_target *ti, struct dm_dev *d);
 /*
  * Target features
  */
-#define DM_TARGET_SUPPORTS_BARRIERS 0x00000001
 
 struct target_type {
 	uint64_t features;