diff options
| -rw-r--r-- | Documentation/device-mapper/thin-provisioning.txt | 39 | ||||
| -rw-r--r-- | drivers/md/dm-thin.c | 85 |
2 files changed, 109 insertions, 15 deletions
diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt index a119fbd..310c120 100644 --- a/Documentation/device-mapper/thin-provisioning.txt +++ b/Documentation/device-mapper/thin-provisioning.txt @@ -169,6 +169,38 @@ 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 +thinly-provisioned volume. Any read to an unprovisioned area of the +thin device will be passed through to the origin. Writes trigger +the allocation of new blocks as usual. + +One use case for this is VM hosts that want to run guests on +thinly-provisioned 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 may write to the thin device and take internal snapshots +of the thin volume. + +i) Creating a snapshot of an external device + + This is the same as creating a thin device. + You don't mention the origin at this stage. + + dmsetup message /dev/mapper/pool 0 "create_thin 0" + +ii) Using a snapshot of an external device. + + Append an extra parameter to the thin target specifying the origin: + + dmsetup create snap --table "0 2097152 thin /dev/mapper/pool 0 /dev/image" + + N.B. All descendants (internal snapshots) of this snapshot require the + same extra origin parameter. + Deactivation ------------ @@ -254,7 +286,7 @@ iii) Messages i) Constructor - thin <pool dev> <dev id> + thin <pool dev> <dev id> [<external origin dev>] pool dev: the thin-pool device, e.g. /dev/mapper/my_pool or 253:0 @@ -263,6 +295,11 @@ i) Constructor the internal device identifier of the device to be activated. + external origin dev: + an optional block device outside the pool to be treated as a + read-only snapshot origin: reads to unprovisioned areas of the + thin target will be mapped to this device. + 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 2378ee8..2d9e755 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -549,6 +549,7 @@ struct pool_c { */ struct thin_c { struct dm_dev *pool_dev; + struct dm_dev *origin_dev; dm_thin_id dev_id; struct pool *pool; @@ -666,14 +667,16 @@ 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(). @@ -686,6 +689,19 @@ static void remap_and_issue(struct thin_c *tc, struct bio *bio, generic_make_request(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. @@ -932,7 +948,8 @@ 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; @@ -964,7 +981,7 @@ 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; @@ -982,6 +999,22 @@ 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) @@ -1128,8 +1161,8 @@ 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: @@ -1203,7 +1236,10 @@ 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: @@ -1254,7 +1290,11 @@ 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: @@ -2237,6 +2277,8 @@ 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); @@ -2245,21 +2287,22 @@ 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; @@ -2272,6 +2315,15 @@ 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"; @@ -2324,6 +2376,9 @@ 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); @@ -2382,6 +2437,8 @@ static int thin_status(struct dm_target *ti, status_type_t type, DMEMIT("%s %lu", format_dev_t(buf, tc->pool_dev->bdev->bd_dev), (unsigned long) tc->dev_id); + if (tc->origin_dev) + DMEMIT(" %s", format_dev_t(buf, tc->origin_dev->bdev->bd_dev)); break; } } @@ -2419,7 +2476,7 @@ static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits) static struct target_type thin_target = { .name = "thin", - .version = {1, 0, 0}, + .version = {1, 1, 0}, .module = THIS_MODULE, .ctr = thin_ctr, .dtr = thin_dtr, |
