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btrfs: reject devices with CHANGING_FSID_V2

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The BTRFS_SUPER_FLAG_CHANGING_FSID_V2 flag indicates a transient state
where the device in the userspace btrfstune -m|-M operation failed to
complete changing the fsid.

This flag makes the kernel to automatically determine the other
partner devices to which a given device can be associated, based on the
fsid, metadata_uuid and generation values.

btrfstune -m|M feature is especially useful in virtual cloud setups, where
compute instances (disk images) are quickly copied, fsid changed, and
launched. Given numerous disk images with the same metadata_uuid but
different fsid, there's no clear way a device can be correctly assembled
with the proper partners when the CHANGING_FSID_V2 flag is set. So, the
disk could be assembled incorrectly, as in the example below:

Before this patch:

Consider the following two filesystems:
   /dev/loop[2-3] are raw copies of /dev/loop[0-1] and the btrsftune -m
operation fails.

In this scenario, as the /dev/loop0's fsid change is interrupted, and the
CHANGING_FSID_V2 flag is set as shown below.

  $ p="device|devid|^metadata_uuid|^fsid|^incom|^generation|^flags"

  $ btrfs inspect dump-super /dev/loop0 | egrep '$p'
  superblock: bytenr=65536, device=/dev/loop0
  flags			0x1000000001
  fsid			7d4b4b93-2b27-4432-b4e4-4be1fbccbd45
  metadata_uuid		bb040a9f-233a-4de2-ad84-49aa5a28059b
  generation		9
  num_devices		2
  incompat_flags	0x741
  dev_item.devid	1

  $ btrfs inspect dump-super /dev/loop1 | egrep '$p'
  superblock: bytenr=65536, device=/dev/loop1
  flags			0x1
  fsid			11d2af4d-1b71-45a9-83f6-f2100766939d
  metadata_uuid		bb040a9f-233a-4de2-ad84-49aa5a28059b
  generation		10
  num_devices		2
  incompat_flags	0x741
  dev_item.devid	2

  $ btrfs inspect dump-super /dev/loop2 | egrep '$p'
  superblock: bytenr=65536, device=/dev/loop2
  flags			0x1
  fsid			7d4b4b93-2b27-4432-b4e4-4be1fbccbd45
  metadata_uuid		bb040a9f-233a-4de2-ad84-49aa5a28059b
  generation		8
  num_devices		2
  incompat_flags	0x741
  dev_item.devid	1

  $ btrfs inspect dump-super /dev/loop3 | egrep '$p'
  superblock: bytenr=65536, device=/dev/loop3
  flags			0x1
  fsid			7d4b4b93-2b27-4432-b4e4-4be1fbccbd45
  metadata_uuid		bb040a9f-233a-4de2-ad84-49aa5a28059b
  generation		8
  num_devices		2
  incompat_flags	0x741
  dev_item.devid	2

It is normal that some devices aren't instantly discovered during
system boot or iSCSI discovery. The controlled scan below demonstrates
this.

  $ btrfs device scan --forget
  $ btrfs device scan /dev/loop0
  Scanning for btrfs filesystems on '/dev/loop0'
  $ mount /dev/loop3 /btrfs
  $ btrfs filesystem show -m
  Label: none  uuid: 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45
	Total devices 2 FS bytes used 144.00KiB
	devid    1 size 300.00MiB used 48.00MiB path /dev/loop0
	devid    2 size 300.00MiB used 40.00MiB path /dev/loop3

/dev/loop0 and /dev/loop3 are incorrectly partnered.

This kernel patch removes functions and code connected to the
CHANGING_FSID_V2 flag.

With this patch, now devices with the CHANGING_FSID_V2 flag are rejected.
And its partner will fail to mount with the extra -o degraded option.
The check is removed from open_ctree(), devices are rejected during
scanning which in turn fails the mount.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Anand Jain 2023-09-21 05:51:13 +08:00 committed by David Sterba
parent ab7c8bbf3a
commit 197a9ecee6
2 changed files with 7 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/btrfs/disk-io.c
View File

@ -3172,7 +3172,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
u32 nodesize;
u32 stripesize;
u64 generation;
u64 features;
u16 csum_type;
struct btrfs_super_block *disk_super;
struct btrfs_fs_info *fs_info = btrfs_sb(sb);
@ -3254,15 +3253,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
disk_super = fs_info->super_copy;
features = btrfs_super_flags(disk_super);
if (features & BTRFS_SUPER_FLAG_CHANGING_FSID_V2) {
features &= ~BTRFS_SUPER_FLAG_CHANGING_FSID_V2;
btrfs_set_super_flags(disk_super, features);
btrfs_info(fs_info,
"found metadata UUID change in progress flag, clearing");
}
memcpy(fs_info->super_for_commit, fs_info->super_copy,
sizeof(*fs_info->super_for_commit));

7
fs/btrfs/volumes.c
View File

@ -791,6 +791,13 @@ static noinline struct btrfs_device *device_list_add(const char *path,
bool fsid_change_in_progress = (btrfs_super_flags(disk_super) &
BTRFS_SUPER_FLAG_CHANGING_FSID_V2);
if (fsid_change_in_progress) {
btrfs_err(NULL,
"device %s has incomplete metadata_uuid change, please use btrfstune to complete",
path);
return ERR_PTR(-EAGAIN);
}
error = lookup_bdev(path, &path_devt);
if (error) {
btrfs_err(NULL, "failed to lookup block device for path %s: %d",