From 8682f7f9688b3b2f0b957c1796cbca5dd8c29a8a Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Thu, 10 Dec 2009 23:52:30 +0000 Subject: [PATCH] --- yaml --- r: 176571 b: refs/heads/master c: d698aa4500aa3ca9559142060caf0f79da998744 h: refs/heads/master i: 176569: 44d0f13823792b7333c3e6120f16bc3e2a48e0b5 176567: 60baedf78d4c1f7b9cdc73c536b58b5ee9a1db03 v: v3 --- [refs] | 2 +- .../Documentation/device-mapper/snapshot.txt | 60 +++++++++++++++++-- trunk/drivers/md/dm-snap.c | 53 ++++++++++++---- 3 files changed, 97 insertions(+), 18 deletions(-) diff --git a/[refs] b/[refs] index 35f7ba05f382..1dfebcedd13b 100644 --- a/[refs] +++ b/[refs] @@ -1,2 +1,2 @@ --- -refs/heads/master: 4454a6216f75a9ef8c4bd0a65e34b101f725ef1e +refs/heads/master: d698aa4500aa3ca9559142060caf0f79da998744 diff --git a/trunk/Documentation/device-mapper/snapshot.txt b/trunk/Documentation/device-mapper/snapshot.txt index a5009c8300f3..e3a77b215135 100644 --- a/trunk/Documentation/device-mapper/snapshot.txt +++ b/trunk/Documentation/device-mapper/snapshot.txt @@ -8,13 +8,19 @@ the block device which are also writable without interfering with the original content; *) To create device "forks", i.e. multiple different versions of the same data stream. +*) To merge a snapshot of a block device back into the snapshot's origin +device. +In the first two cases, dm copies only the chunks of data that get +changed and uses a separate copy-on-write (COW) block device for +storage. -In both cases, dm copies only the chunks of data that get changed and -uses a separate copy-on-write (COW) block device for storage. +For snapshot merge the contents of the COW storage are merged back into +the origin device. -There are two dm targets available: snapshot and snapshot-origin. +There are three dm targets available: +snapshot, snapshot-origin, and snapshot-merge. *) snapshot-origin @@ -40,8 +46,25 @@ The difference is that for transient snapshots less metadata must be saved on disk - they can be kept in memory by the kernel. -How this is used by LVM2 -======================== +* snapshot-merge + +takes the same table arguments as the snapshot target except it only +works with persistent snapshots. This target assumes the role of the +"snapshot-origin" target and must not be loaded if the "snapshot-origin" +is still present for . + +Creates a merging snapshot that takes control of the changed chunks +stored in the of an existing snapshot, through a handover +procedure, and merges these chunks back into the . Once merging +has started (in the background) the may be opened and the merge +will continue while I/O is flowing to it. Changes to the are +deferred until the merging snapshot's corresponding chunk(s) have been +merged. Once merging has started the snapshot device, associated with +the "snapshot" target, will return -EIO when accessed. + + +How snapshot is used by LVM2 +============================ When you create the first LVM2 snapshot of a volume, four dm devices are used: 1) a device containing the original mapping table of the source volume; @@ -72,3 +95,30 @@ brw------- 1 root root 254, 12 29 ago 18:15 /dev/mapper/volumeGroup-snap-cow brw------- 1 root root 254, 13 29 ago 18:15 /dev/mapper/volumeGroup-snap brw------- 1 root root 254, 10 29 ago 18:14 /dev/mapper/volumeGroup-base + +How snapshot-merge is used by LVM2 +================================== +A merging snapshot assumes the role of the "snapshot-origin" while +merging. As such the "snapshot-origin" is replaced with +"snapshot-merge". The "-real" device is not changed and the "-cow" +device is renamed to -cow to aid LVM2's cleanup of the +merging snapshot after it completes. The "snapshot" that hands over its +COW device to the "snapshot-merge" is deactivated (unless using lvchange +--refresh); but if it is left active it will simply return I/O errors. + +A snapshot will merge into its origin with the following command: + +lvconvert --merge volumeGroup/snap + +we'll now have this situation: + +# dmsetup table|grep volumeGroup + +volumeGroup-base-real: 0 2097152 linear 8:19 384 +volumeGroup-base-cow: 0 204800 linear 8:19 2097536 +volumeGroup-base: 0 2097152 snapshot-merge 254:11 254:12 P 16 + +# ls -lL /dev/mapper/volumeGroup-* +brw------- 1 root root 254, 11 29 ago 18:15 /dev/mapper/volumeGroup-base-real +brw------- 1 root root 254, 12 29 ago 18:16 /dev/mapper/volumeGroup-base-cow +brw------- 1 root root 254, 10 29 ago 18:16 /dev/mapper/volumeGroup-base diff --git a/trunk/drivers/md/dm-snap.c b/trunk/drivers/md/dm-snap.c index 288994ee7142..446827f98236 100644 --- a/trunk/drivers/md/dm-snap.c +++ b/trunk/drivers/md/dm-snap.c @@ -25,6 +25,11 @@ #define DM_MSG_PREFIX "snapshots" +static const char dm_snapshot_merge_target_name[] = "snapshot-merge"; + +#define dm_target_is_snapshot_merge(ti) \ + ((ti)->type->name == dm_snapshot_merge_target_name) + /* * The percentage increment we will wake up users at */ @@ -1743,6 +1748,21 @@ static struct target_type snapshot_target = { .iterate_devices = snapshot_iterate_devices, }; +static struct target_type merge_target = { + .name = dm_snapshot_merge_target_name, + .version = {1, 0, 0}, + .module = THIS_MODULE, + .ctr = snapshot_ctr, + .dtr = snapshot_dtr, + .map = snapshot_map, + .end_io = snapshot_end_io, + .postsuspend = snapshot_postsuspend, + .preresume = snapshot_preresume, + .resume = snapshot_resume, + .status = snapshot_status, + .iterate_devices = snapshot_iterate_devices, +}; + static int __init dm_snapshot_init(void) { int r; @@ -1754,7 +1774,7 @@ static int __init dm_snapshot_init(void) } r = dm_register_target(&snapshot_target); - if (r) { + if (r < 0) { DMERR("snapshot target register failed %d", r); goto bad_register_snapshot_target; } @@ -1762,34 +1782,40 @@ static int __init dm_snapshot_init(void) r = dm_register_target(&origin_target); if (r < 0) { DMERR("Origin target register failed %d", r); - goto bad1; + goto bad_register_origin_target; + } + + r = dm_register_target(&merge_target); + if (r < 0) { + DMERR("Merge target register failed %d", r); + goto bad_register_merge_target; } r = init_origin_hash(); if (r) { DMERR("init_origin_hash failed."); - goto bad2; + goto bad_origin_hash; } exception_cache = KMEM_CACHE(dm_exception, 0); if (!exception_cache) { DMERR("Couldn't create exception cache."); r = -ENOMEM; - goto bad3; + goto bad_exception_cache; } pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0); if (!pending_cache) { DMERR("Couldn't create pending cache."); r = -ENOMEM; - goto bad4; + goto bad_pending_cache; } tracked_chunk_cache = KMEM_CACHE(dm_snap_tracked_chunk, 0); if (!tracked_chunk_cache) { DMERR("Couldn't create cache to track chunks in use."); r = -ENOMEM; - goto bad5; + goto bad_tracked_chunk_cache; } ksnapd = create_singlethread_workqueue("ksnapd"); @@ -1803,19 +1829,21 @@ static int __init dm_snapshot_init(void) bad_pending_pool: kmem_cache_destroy(tracked_chunk_cache); -bad5: +bad_tracked_chunk_cache: kmem_cache_destroy(pending_cache); -bad4: +bad_pending_cache: kmem_cache_destroy(exception_cache); -bad3: +bad_exception_cache: exit_origin_hash(); -bad2: +bad_origin_hash: + dm_unregister_target(&merge_target); +bad_register_merge_target: dm_unregister_target(&origin_target); -bad1: +bad_register_origin_target: dm_unregister_target(&snapshot_target); - bad_register_snapshot_target: dm_exception_store_exit(); + return r; } @@ -1825,6 +1853,7 @@ static void __exit dm_snapshot_exit(void) dm_unregister_target(&snapshot_target); dm_unregister_target(&origin_target); + dm_unregister_target(&merge_target); exit_origin_hash(); kmem_cache_destroy(pending_cache);