From cc8394d86f045b86ff303d3c9e4ce47d97148951 Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Sun, 3 Jun 2012 00:30:01 +0100 Subject: dm thin: provide userspace access to pool metadata This patch implements two new messages that can be sent to the thin pool target allowing it to take a snapshot of the _metadata_. This, read-only snapshot can be accessed by userland, concurrently with the live target. Only one metadata snapshot can be held at a time. The pool's status line will give the block location for the current msnap. Since version 0.1.5 of the userland thin provisioning tools, the thin_dump program displays the msnap as follows: thin_dump -m Available here: https://github.com/jthornber/thin-provisioning-tools Now that userland can access the metadata we can do various things that have traditionally been kernel side tasks: i) Incremental backups. By using metadata snapshots we can work out what blocks have changed over time. Combined with data snapshots we can ensure the data doesn't change while we back it up. A short proof of concept script can be found here: https://github.com/jthornber/thinp-test-suite/blob/master/incremental_backup_example.rb ii) Migration of thin devices from one pool to another. iii) Merging snapshots back into an external origin. iv) Asyncronous replication. Signed-off-by: Joe Thornber Signed-off-by: Alasdair G Kergon --- drivers/md/dm-thin-metadata.c | 136 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 130 insertions(+), 6 deletions(-) (limited to 'drivers/md/dm-thin-metadata.c') diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c index 737d388..3e2907f 100644 --- a/drivers/md/dm-thin-metadata.c +++ b/drivers/md/dm-thin-metadata.c @@ -1082,12 +1082,89 @@ int dm_pool_get_metadata_transaction_id(struct dm_pool_metadata *pmd, return 0; } -static int __get_held_metadata_root(struct dm_pool_metadata *pmd, - dm_block_t *result) +static int __reserve_metadata_snap(struct dm_pool_metadata *pmd) +{ + int r, inc; + struct thin_disk_superblock *disk_super; + struct dm_block *copy, *sblock; + dm_block_t held_root; + + /* + * Copy the superblock. + */ + dm_sm_inc_block(pmd->metadata_sm, THIN_SUPERBLOCK_LOCATION); + r = dm_tm_shadow_block(pmd->tm, THIN_SUPERBLOCK_LOCATION, + &sb_validator, ©, &inc); + if (r) + return r; + + BUG_ON(!inc); + + held_root = dm_block_location(copy); + disk_super = dm_block_data(copy); + + if (le64_to_cpu(disk_super->held_root)) { + DMWARN("Pool metadata snapshot already exists: release this before taking another."); + + dm_tm_dec(pmd->tm, held_root); + dm_tm_unlock(pmd->tm, copy); + pmd->need_commit = 1; + + return -EBUSY; + } + + /* + * Wipe the spacemap since we're not publishing this. + */ + memset(&disk_super->data_space_map_root, 0, + sizeof(disk_super->data_space_map_root)); + memset(&disk_super->metadata_space_map_root, 0, + sizeof(disk_super->metadata_space_map_root)); + + /* + * Increment the data structures that need to be preserved. + */ + dm_tm_inc(pmd->tm, le64_to_cpu(disk_super->data_mapping_root)); + dm_tm_inc(pmd->tm, le64_to_cpu(disk_super->device_details_root)); + dm_tm_unlock(pmd->tm, copy); + + /* + * Write the held root into the superblock. + */ + r = dm_bm_write_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION, + &sb_validator, &sblock); + if (r) { + dm_tm_dec(pmd->tm, held_root); + pmd->need_commit = 1; + return r; + } + + disk_super = dm_block_data(sblock); + disk_super->held_root = cpu_to_le64(held_root); + dm_bm_unlock(sblock); + + pmd->need_commit = 1; + + return 0; +} + +int dm_pool_reserve_metadata_snap(struct dm_pool_metadata *pmd) +{ + int r; + + down_write(&pmd->root_lock); + r = __reserve_metadata_snap(pmd); + up_write(&pmd->root_lock); + + return r; +} + +static int __release_metadata_snap(struct dm_pool_metadata *pmd) { int r; struct thin_disk_superblock *disk_super; - struct dm_block *sblock; + struct dm_block *sblock, *copy; + dm_block_t held_root; r = dm_bm_write_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION, &sb_validator, &sblock); @@ -1095,18 +1172,65 @@ static int __get_held_metadata_root(struct dm_pool_metadata *pmd, return r; disk_super = dm_block_data(sblock); + held_root = le64_to_cpu(disk_super->held_root); + disk_super->held_root = cpu_to_le64(0); + pmd->need_commit = 1; + + dm_bm_unlock(sblock); + + if (!held_root) { + DMWARN("No pool metadata snapshot found: nothing to release."); + return -EINVAL; + } + + r = dm_tm_read_lock(pmd->tm, held_root, &sb_validator, ©); + if (r) + return r; + + disk_super = dm_block_data(copy); + dm_sm_dec_block(pmd->metadata_sm, le64_to_cpu(disk_super->data_mapping_root)); + dm_sm_dec_block(pmd->metadata_sm, le64_to_cpu(disk_super->device_details_root)); + dm_sm_dec_block(pmd->metadata_sm, held_root); + + return dm_tm_unlock(pmd->tm, copy); +} + +int dm_pool_release_metadata_snap(struct dm_pool_metadata *pmd) +{ + int r; + + down_write(&pmd->root_lock); + r = __release_metadata_snap(pmd); + up_write(&pmd->root_lock); + + return r; +} + +static int __get_metadata_snap(struct dm_pool_metadata *pmd, + dm_block_t *result) +{ + int r; + struct thin_disk_superblock *disk_super; + struct dm_block *sblock; + + r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION, + &sb_validator, &sblock); + if (r) + return r; + + disk_super = dm_block_data(sblock); *result = le64_to_cpu(disk_super->held_root); return dm_bm_unlock(sblock); } -int dm_pool_get_held_metadata_root(struct dm_pool_metadata *pmd, - dm_block_t *result) +int dm_pool_get_metadata_snap(struct dm_pool_metadata *pmd, + dm_block_t *result) { int r; down_read(&pmd->root_lock); - r = __get_held_metadata_root(pmd, result); + r = __get_metadata_snap(pmd, result); up_read(&pmd->root_lock); return r; -- cgit v1.1