dm: support barriers on simple devices

Implement barrier support for single device DM devices This patch implements barrier support in DM for the common case of dm linear just remapping a single underlying device. In this case we can safely pass the barrier through because there can be no reordering between devices. NB. Any DM device might cease to support barriers if it gets reconfigured so code must continue to allow for a possible -EOPNOTSUPP on every barrier bio submitted. - agk Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>

dm: support barriers on simple devices
Implement barrier support for single device DM devices This patch implements barrier support in DM for the common case of dm linear just remapping a single underlying device. In this case we can safely pass the barrier through because there can be no reordering between devices. NB. Any DM device might cease to support barriers if it gets reconfigured so code must continue to allow for a possible -EOPNOTSUPP on every barrier bio submitted. - agk Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Andi Kleen · Alasdair G Kergon
1 parent 7d76345da6
Showing 5 changed files with 33 additions and 10 deletions Side-by-side Diff
drivers/md/dm-linear.c
drivers/md/dm-table.c
drivers/md/dm.c
drivers/md/dm.h
include/linux/device-mapper.h
@@ -142,6 +142,7 @@
 	.status = linear_status,
 	.ioctl  = linear_ioctl,
 	.merge  = linear_merge,
+	.features = DM_TARGET_SUPPORTS_BARRIERS,
 };
  
 int __init dm_linear_init(void)
@@ -38,6 +38,8 @@
 	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 @@
  
 	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 @@
 	/* 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 @@
  
 	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);
@@ -985,6 +998,12 @@
  
 	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);
@@ -835,7 +835,11 @@
 	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);
@@ -918,15 +922,6 @@
 	int rw = bio_data_dir(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);
  
@@ -51,6 +51,7 @@
  * 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.
@@ -112,7 +112,14 @@
 /*
  * 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];
...	...	@@ -142,6 +142,7 @@
142	142	.status = linear_status,
143	143	.ioctl = linear_ioctl,
144	144	.merge = linear_merge,
	145	+ .features = DM_TARGET_SUPPORTS_BARRIERS,
145	146	};
146	147
147	148	int __init dm_linear_init(void)
...	...	@@ -38,6 +38,8 @@
38	38	sector_t *highs;
39	39	struct dm_target *targets;
40	40
	41	+ unsigned barriers_supported:1;
	42	+
41	43	/*
42	44	* Indicates the rw permissions for the new logical
43	45	* device. This should be a combination of FMODE_READ
...	...	@@ -227,6 +229,7 @@
227	229
228	230	INIT_LIST_HEAD(&t->devices);
229	231	atomic_set(&t->holders, 1);
	232	+ t->barriers_supported = 1;
230	233
231	234	if (!num_targets)
232	235	num_targets = KEYS_PER_NODE;
...	...	@@ -728,6 +731,10 @@
728	731	/* FIXME: the plan is to combine high here and then have
729	732	* the merge fn apply the target level restrictions. */
730	733	combine_restrictions_low(&t->limits, &tgt->limits);
	734	+
	735	+ if (!(tgt->type->features & DM_TARGET_SUPPORTS_BARRIERS))
	736	+ t->barriers_supported = 0;
	737	+
731	738	return 0;
732	739
733	740	bad:
...	...	@@ -772,6 +779,12 @@
772	779
773	780	check_for_valid_limits(&t->limits);
774	781
	782	+ /*
	783	+ * We only support barriers if there is exactly one underlying device.
	784	+ */
	785	+ if (!list_is_singular(&t->devices))
	786	+ t->barriers_supported = 0;
	787	+
775	788	/* how many indexes will the btree have ? */
776	789	leaf_nodes = dm_div_up(t->num_targets, KEYS_PER_NODE);
777	790	t->depth = 1 + int_log(leaf_nodes, CHILDREN_PER_NODE);
...	...	@@ -985,6 +998,12 @@
985	998
986	999	return t->md;
987	1000	}
	1001	+
	1002	+int dm_table_barrier_ok(struct dm_table *t)
	1003	+{
	1004	+ return t->barriers_supported;
	1005	+}
	1006	+EXPORT_SYMBOL(dm_table_barrier_ok);
988	1007
989	1008	EXPORT_SYMBOL(dm_vcalloc);
990	1009	EXPORT_SYMBOL(dm_get_device);
...	...	@@ -835,7 +835,11 @@
835	835	ci.map = dm_get_table(md);
836	836	if (unlikely(!ci.map))
837	837	return -EIO;
838		-
	838	+ if (unlikely(bio_barrier(bio) && !dm_table_barrier_ok(ci.map))) {
	839	+ dm_table_put(ci.map);
	840	+ bio_endio(bio, -EOPNOTSUPP);
	841	+ return 0;
	842	+ }
839	843	ci.md = md;
840	844	ci.bio = bio;
841	845	ci.io = alloc_io(md);
...	...	@@ -918,15 +922,6 @@
918	922	int rw = bio_data_dir(bio);
919	923	struct mapped_device *md = q->queuedata;
920	924	int cpu;
921		-
922		- /*
923		- * There is no use in forwarding any barrier request since we can't
924		- * guarantee it is (or can be) handled by the targets correctly.
925		- */
926		- if (unlikely(bio_barrier(bio))) {
927		- bio_endio(bio, -EOPNOTSUPP);
928		- return 0;
929		- }
930	925
931	926	down_read(&md->io_lock);
932	927
...	...	@@ -51,6 +51,7 @@
51	51	* To check the return value from dm_table_find_target().
52	52	*/
53	53	#define dm_target_is_valid(t) ((t)->table)
	54	+int dm_table_barrier_ok(struct dm_table *t);
54	55
55	56	/*-----------------------------------------------------------------
56	57	* A registry of target types.
...	...	@@ -112,7 +112,14 @@
112	112	/*
113	113	* Information about a target type
114	114	*/
	115	+
	116	+/*
	117	+ * Target features
	118	+ */
	119	+#define DM_TARGET_SUPPORTS_BARRIERS 0x00000001
	120	+
115	121	struct target_type {
	122	+ uint64_t features;
116	123	const char *name;
117	124	struct module *module;
118	125	unsigned version[3];