---
Documentation/device-mapper/thin-provisioning.txt | 38 ++++++++++-
drivers/md/dm-thin.c | 81 +++++++++++++++++----
2 files changed, 105 insertions(+), 14 deletions(-)
diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index 801d9d1..60fc5cf 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -167,6 +167,38 @@ ii) Using an internal snapshot.
dmsetup create snap --table "0 2097152 thin /dev/mapper/pool 1"
+External snapshots
+------------------
+
+You can use an external, _read only_, device as an origin for a thin
+device. Any read to an unprovisioned area of the thin device will be
+passed through to the origin. Writes trigger allocation of new blocks
+as usual.
+
+One possible use case for this would be VM hosts who want to run
+guests on thinp volumes, but have the base image on another device
+(possibly shared between many VMs).
+
+You must not write to the origin device if you use this technique! Of
+course you can write to the thin device, and take internal snapshots
+of the thin.
+
+i) Creating an external snapshot
+
+ Same as creating a thin device. You don't need to mention the
+ origin at this stage.
+
+ dmsetup message /dev/mapper/pool 0 "create_thin 0"
+
+ii) Using an external snapshot.
+
+ Add an extra parameter to the thin target specifying the origin:
+
+ dmsetup create snap --table "0 2097152 thin /dev/mapper/pool 0 /dev/image"
+
+ All descendants (internal snapshots) of an external snapshot will
+ need the extra origin argument.
+
Deactivation
------------
@@ -262,7 +294,7 @@ iii) Messages
i) Constructor
- thin <pool dev> <dev id>
+ thin <pool dev> <dev id> [external origin id]
pool dev:
the thin-pool device, e.g. /dev/mapper/my_pool or 253:0
@@ -271,6 +303,10 @@ i) Constructor
the internal device identifier of the device to be
activated.
+ external origin dev:
+ a block device; reads to unprovisioned areas of the thin target
+ will be mapped to here.
+
The pool doesn't store any size against the thin devices. If you
load a thin target that is smaller than you've been using previously,
then you'll have no access to blocks mapped beyond the end. If you
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 19de11a..922ebf2 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -537,6 +537,7 @@ struct pool_c {
*/
struct thin_c {
struct dm_dev *pool_dev;
+ struct dm_dev *origin_dev;
dm_thin_id dev_id;
struct pool *pool;
@@ -654,14 +655,16 @@ static void remap(struct thin_c *tc, struct bio *bio, dm_block_t block)
(bio->bi_sector & pool->offset_mask);
}
-static void remap_and_issue(struct thin_c *tc, struct bio *bio,
- dm_block_t block)
+static void remap_to_origin(struct thin_c *tc, struct bio *bio)
+{
+ bio->bi_bdev = tc->origin_dev->bdev;
+}
+
+static void issue(struct thin_c *tc, struct bio *bio)
{
struct pool *pool = tc->pool;
unsigned long flags;
- remap(tc, bio, block);
-
/*
* Batch together any FUA/FLUSH bios we find and then issue
* a single commit for them in process_deferred_bios().
@@ -676,6 +679,19 @@ static void remap_and_issue(struct thin_c *tc, struct bio *bio,
}
}
+static void remap_to_origin_and_issue(struct thin_c *tc, struct bio *bio)
+{
+ remap_to_origin(tc, bio);
+ issue(tc, bio);
+}
+
+static void remap_and_issue(struct thin_c *tc, struct bio *bio,
+ dm_block_t block)
+{
+ remap(tc, bio, block);
+ issue(tc, bio);
+}
+
/*
* wake_worker() is used when new work is queued and when pool_resume is
* ready to continue deferred IO processing.
@@ -927,7 +943,8 @@ static struct new_mapping *get_next_mapping(struct pool *pool)
}
static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
- dm_block_t data_origin, dm_block_t data_dest,
+ struct dm_dev *origin, dm_block_t data_origin,
+ dm_block_t data_dest,
struct cell *cell, struct bio *bio)
{
int r;
@@ -959,7 +976,7 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
} else {
struct dm_io_region from, to;
- from.bdev = tc->pool_dev->bdev;
+ from.bdev = origin->bdev;
from.sector = data_origin * pool->sectors_per_block;
from.count = pool->sectors_per_block;
@@ -977,6 +994,22 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
}
}
+static void schedule_internal_copy(struct thin_c *tc, dm_block_t virt_block,
+ dm_block_t data_origin, dm_block_t data_dest,
+ struct cell *cell, struct bio *bio)
+{
+ schedule_copy(tc, virt_block, tc->pool_dev,
+ data_origin, data_dest, cell, bio);
+}
+
+static void schedule_external_copy(struct thin_c *tc, dm_block_t virt_block,
+ dm_block_t data_dest,
+ struct cell *cell, struct bio *bio)
+{
+ schedule_copy(tc, virt_block, tc->origin_dev,
+ virt_block, data_dest, cell, bio);
+}
+
static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
dm_block_t data_block, struct cell *cell,
struct bio *bio)
@@ -1123,8 +1156,8 @@ static void break_sharing(struct thin_c *tc, struct bio *bio, dm_block_t block,
r = alloc_data_block(tc, &data_block);
switch (r) {
case 0:
- schedule_copy(tc, block, lookup_result->block,
- data_block, cell, bio);
+ schedule_internal_copy(tc, block, lookup_result->block,
+ data_block, cell, bio);
break;
case -ENOSPC:
@@ -1198,7 +1231,10 @@ static void provision_block(struct thin_c *tc, struct bio *bio, dm_block_t block
r = alloc_data_block(tc, &data_block);
switch (r) {
case 0:
- schedule_zero(tc, block, data_block, cell, bio);
+ if (tc->origin_dev)
+ schedule_external_copy(tc, block, data_block, cell, bio);
+ else
+ schedule_zero(tc, block, data_block, cell, bio);
break;
case -ENOSPC:
@@ -1249,7 +1285,11 @@ static void process_bio(struct thin_c *tc, struct bio *bio)
break;
case -ENODATA:
- provision_block(tc, bio, block, cell);
+ if (bio_data_dir(bio) == READ && tc->origin_dev) {
+ cell_release_singleton(cell, bio);
+ remap_to_origin_and_issue(tc, bio);
+ } else
+ provision_block(tc, bio, block, cell);
break;
default:
@@ -2235,6 +2275,8 @@ static void thin_dtr(struct dm_target *ti)
__pool_dec(tc->pool);
dm_pool_close_thin_device(tc->td);
dm_put_device(ti, tc->pool_dev);
+ if (tc->origin_dev)
+ dm_put_device(ti, tc->origin_dev);
kfree(tc);
mutex_unlock(&dm_thin_pool_table.mutex);
@@ -2243,21 +2285,22 @@ static void thin_dtr(struct dm_target *ti)
/*
* Thin target parameters:
*
- * <pool_dev> <dev_id>
+ * <pool_dev> <dev_id> [origin_dev]
*
* pool_dev: the path to the pool (eg, /dev/mapper/my_pool)
* dev_id: the internal device identifier
+ * origin_dev: a device external to the pool that should act as the origin
*/
static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
int r;
struct thin_c *tc;
- struct dm_dev *pool_dev;
+ struct dm_dev *pool_dev, *origin_dev;
struct mapped_device *pool_md;
mutex_lock(&dm_thin_pool_table.mutex);
- if (argc != 2) {
+ if (argc != 2 && argc != 3) {
ti->error = "Invalid argument count";
r = -EINVAL;
goto out_unlock;
@@ -2270,6 +2313,15 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
goto out_unlock;
}
+ if (argc == 3) {
+ r = dm_get_device(ti, argv[2], FMODE_READ, &origin_dev);
+ if (r) {
+ ti->error = "Error opening origin device";
+ goto bad_origin_dev;
+ }
+ tc->origin_dev = origin_dev;
+ }
+
r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &pool_dev);
if (r) {
ti->error = "Error opening pool device";
@@ -2322,6 +2374,9 @@ bad_pool_lookup:
bad_common:
dm_put_device(ti, tc->pool_dev);
bad_pool_dev:
+ if (tc->origin_dev)
+ dm_put_device(ti, tc->origin_dev);
+bad_origin_dev:
kfree(tc);
out_unlock:
mutex_unlock(&dm_thin_pool_table.mutex);
--
1.7.5.4
--
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