Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755994AbZKTU14 (ORCPT ); Fri, 20 Nov 2009 15:27:56 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755481AbZKTU1y (ORCPT ); Fri, 20 Nov 2009 15:27:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:13595 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754870AbZKTU1v (ORCPT ); Fri, 20 Nov 2009 15:27:51 -0500 From: Mike Snitzer To: dm-devel@redhat.com Cc: linux-kernel@vger.kernel.org, Mikulas Patocka Subject: [PATCH v4 05/13] dm snapshot: add snapshot-merge target Date: Fri, 20 Nov 2009 15:27:45 -0500 Message-Id: <1258748873-24185-6-git-send-email-snitzer@redhat.com> In-Reply-To: <1258748873-24185-1-git-send-email-snitzer@redhat.com> References: <1258748873-24185-1-git-send-email-snitzer@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7388 Lines: 226 From: Mikulas Patocka The snapshot-merge target allows a snapshot to be merged back into the snapshot's origin device. One expected use of snapshot merging is the rollback of a root filesystem after system upgrades (e.g.: yum update). snapshot-merge enables "system rollback" support for any filesystem that is using the associated DM devices. Add snapshot-merge target management to both dm_snapshot_init() and dm_snapshot_exit(). As an initial place-holder, snapshot-merge is identical to the snapshot target. Add "snapshot-merge" to Documentation/device-mapper/snapshot.txt Signed-off-by: Mikulas Patocka Signed-off-by: Mike Snitzer --- Documentation/device-mapper/snapshot.txt | 52 +++++++++++++++++++++++++++--- drivers/md/dm-snap.c | 48 ++++++++++++++++++++------- 2 files changed, 83 insertions(+), 17 deletions(-) diff --git a/Documentation/device-mapper/snapshot.txt b/Documentation/device-mapper/snapshot.txt index a5009c8..ec6c883 100644 --- a/Documentation/device-mapper/snapshot.txt +++ b/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 +46,17 @@ 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. 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 . + + +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 +87,30 @@ 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 aid LVM2's cleanup of the merging snapshot after it +completes. The "snapshot" that hands over its COW device to the +"snapshot-merge" is generally deactivated; 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/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index ad95039..e8a1107 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -1664,6 +1664,21 @@ static struct target_type snapshot_target = { .iterate_devices = snapshot_iterate_devices, }; +static struct target_type merge_target = { + .name = "snapshot-merge", + .version = {1, 9, 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; @@ -1675,7 +1690,7 @@ 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; } @@ -1683,34 +1698,40 @@ 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"); @@ -1724,19 +1745,21 @@ 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; } @@ -1746,6 +1769,7 @@ 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); -- 1.6.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/