path: root/drivers/md/dm-thin-metadata.h
diff options
authorJoe Thornber <ejt@redhat.com>2012-06-03 00:30:01 +0100
committerAlasdair G Kergon <agk@redhat.com>2012-06-03 00:30:01 +0100
commitcc8394d86f045b86ff303d3c9e4ce47d97148951 (patch)
treead37143c9709f523fb2ca9fc5ac9de75e9a011f9 /drivers/md/dm-thin-metadata.h
parenta24c25696b7133dd534d7a9436e576af79d9ce3b (diff)
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 <msnap root> <metadata dev> 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 <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'drivers/md/dm-thin-metadata.h')
1 files changed, 10 insertions, 3 deletions
diff --git a/drivers/md/dm-thin-metadata.h b/drivers/md/dm-thin-metadata.h
index ed4725e67c96..b88918ccdaf6 100644
--- a/drivers/md/dm-thin-metadata.h
+++ b/drivers/md/dm-thin-metadata.h
@@ -90,11 +90,18 @@ int dm_pool_get_metadata_transaction_id(struct dm_pool_metadata *pmd,
* Hold/get root for userspace transaction.
+ *
+ * The metadata snapshot is a copy of the current superblock (minus the
+ * space maps). Userland can access the data structures for READ
+ * operations only. A small performance hit is incurred by providing this
+ * copy of the metadata to userland due to extra copy-on-write operations
+ * on the metadata nodes. Release this as soon as you finish with it.
-int dm_pool_hold_metadata_root(struct dm_pool_metadata *pmd);
+int dm_pool_reserve_metadata_snap(struct dm_pool_metadata *pmd);
+int dm_pool_release_metadata_snap(struct dm_pool_metadata *pmd);
-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);
* Actions on a single virtual device.