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>
diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index 79fb53e..bfa107f 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -142,6 +142,7 @@
.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 04e5fd7..ebaaf72 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -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);
@@ -986,6 +999,12 @@
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);
EXPORT_SYMBOL(dm_put_device);
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4882ce7..dd953b1 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -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);
@@ -919,15 +923,6 @@
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 0ade60c..5b5d08b 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -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.
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index c1ba76c..8209e08 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -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];
