Re: Adding a UUID to the top level subvol on an existing filesystem

[Alex MacCuish <alex@maccuish.de>]

I'm using btrbk which has worked successfully for me on other systems. 
In their FAQ (https://github.com/digint/btrbk/blob/master/doc/FAQ.md), 
they state:

---

If your file system was created with btrfs-progs < 4.16, the btrfs root 
subvolume (id=5) has no UUID. You can check this by calling:

|# btrfs subvolume show /mnt/btr_pool / Name: <FS_TREE> UUID: - [...] |

Without a UUID, the snapshots would get no parent_uuid, leaving btrbk 
unable to track parent/child relationships. In this case, btrbk refuses 
to create snapshots and backups.

---

I've asked there on whether this can be worked around but no luck.

Am 10.01.22 um 12:38 schrieb Andrei Borzenkov:
> On 09.01.2022 13:11, Alex MacCuish wrote:
>> For use of send/receive, I need my subvolume id 5 to have a UUID. I see
> You always send read-only snapshot and send/receive is using UUID of this
> snapshot, not of original subvolume. Do you get any error or something
> does not work?
>
>> here (https://www.spinics.net/lists/linux-btrfs/msg76016.html) that it
>> was discussed to add this feature to say btrfstune, but I can't find any
>> option to do it. What's the best way to do this and ensure current
>> subvolumes have the correct parent ID?
>>
>> ---
>>
>> Linux xxx.xxx.xxx 5.15.11-051511-generic #202112220937 SMP Wed Dec 22
>> 10:04:02 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
>>
>> btrfs-progs v5.4.1
>>
>> btrfs fi show
>>
>> Label: 'storage'  uuid: 61538bc8-fc27-4818-9cc9-133938e252da
>>           Total devices 4 FS bytes used 2.35TiB
>>           devid    1 size 1.82TiB used 1.63TiB path /dev/sdd
>>           devid    2 size 1.82TiB used 1.63TiB path /dev/sdc
>>           devid    3 size 1.82TiB used 744.03GiB path /dev/sdb
>>           devid    4 size 931.51GiB used 738.03GiB path /dev/sde
>>
>> btrfs fi df /mnt/storage
>> Data, RAID1: total=2.35TiB, used=2.34TiB
>> System, RAID1: total=32.00MiB, used=368.00KiB
>> Metadata, RAID1: total=5.00GiB, used=4.32GiB
>> GlobalReserve, single: total=512.00MiB, used=0.00B
>>
>> btrfs subvolume show /mnt/storage/
>> /
>>           Name:                   <FS_TREE>
>>           UUID:                   -
>>           Parent UUID:            -
>>           Received UUID:          -
>>           Creation time:          -
>>           Subvolume ID:           5
>>           Generation:             4620363
>>           Gen at creation:        0
>>           Parent ID:              0
>>           Top level ID:           0
>>           Snapshot(s):
>>                                   CN_IMGS
>>                                   CN_PKGS
>>                                   CN_PKGS/.snapshots
>>                                   CN_SHARE
>>                                   CN_SHARE/.snapshots
>>                                   CN_MEDIA
>>                                   CN_MEDIA/.snapshots
>>                                   CN_HOMES
>>                                   CN_HOMES/.snapshots
>>                                   CN_BACKUPS
>>