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| author | Nikolay Borisov <nborisov@suse.com> | 2020-08-12 17:04:36 +0300 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2020-10-07 12:06:58 +0200 |
| commit | 427c8fddb1296dd013d8af5a4957d9d88fb8ab4e (patch) | |
| tree | d2317468e6d0c47eac77755f30754ccf8d363e0f /fs/btrfs/volumes.c | |
| parent | 944d3f9fac61e24e13a056b25974df3831994f29 (diff) | |
| download | linux-427c8fddb1296dd013d8af5a4957d9d88fb8ab4e.tar.bz2 | |
btrfs: document some invariants of seed code
Without good understanding of how seed devices works it's hard to grok
some of what the code in open_seed_devices or btrfs_prepare_sprout does.
Add comments hopefully reducing some of the cognitive load.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/volumes.c')
| -rw-r--r-- | fs/btrfs/volumes.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 2d7c845b8e67..7a39f3aebc53 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -2357,10 +2357,20 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) if (!fs_devices->seeding) return -EINVAL; + /* + * Private copy of the seed devices, anchored at + * fs_info->fs_devices->seed_list + */ seed_devices = alloc_fs_devices(NULL, NULL); if (IS_ERR(seed_devices)) return PTR_ERR(seed_devices); + /* + * It's necessary to retain a copy of the original seed fs_devices in + * fs_uuids so that filesystems which have been seeded can successfully + * reference the seed device from open_seed_devices. This also supports + * multiple fs seed. + */ old_devices = clone_fs_devices(fs_devices); if (IS_ERR(old_devices)) { kfree(seed_devices); @@ -6720,6 +6730,7 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info, lockdep_assert_held(&uuid_mutex); ASSERT(fsid); + /* This will match only for multi-device seed fs */ list_for_each_entry(fs_devices, &fs_info->fs_devices->seed_list, seed_list) if (!memcmp(fs_devices->fsid, fsid, BTRFS_FSID_SIZE)) return fs_devices; @@ -6739,6 +6750,10 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info, return fs_devices; } + /* + * Upon first call for a seed fs fsid, just create a private copy of the + * respective fs_devices and anchor it at fs_info->fs_devices->seed_list + */ fs_devices = clone_fs_devices(fs_devices); if (IS_ERR(fs_devices)) return fs_devices; |