Marc's Public Blog - Linux Hacking

btrfs snapshot dir1/Video_ro.20180220_21:03:41 dir2/Video_ro.20180220_21:03:41 

Later, I wanted to re-establish the btrfs send/receive relationship since it was an 8TB subvolume, and I wanted to avoid having to copy back all the data I already had there. Simply making the destination snapshot read only again did not work

The solution was python-btrfs, and this code: https://github.com/knorrie/python-btrfs/commit/1ace623f95300ecf581b1182780fd6432a46b24d

gargamel:python-btrfs/examples# ./set_received_uuid.py 2afc7a5e-107f-d54b-8929-197b80b70828 31337 1234.5678
/mnt/btrfs_bigbackup/DS1/Video_ro.20180220_21:03:411G
Current subvolume information:
  subvol_id: 94887
  received_uuid: 00000000-0000-0000-0000-000000000000
  stime: 0.0 (1970-01-01T00:00:00)
  stransid: 0
  rtime: 0.0 (1970-01-01T00:00:00)
  rtransid: 0

Setting received subvolume...

Resulting subvolume information:
  subvol_id: 94887
  received_uuid: 2afc7a5e-107f-d54b-8929-197b80b70828
  stime: 1234.5678 (1970-01-01T00:20:34.567800)
  stransid: 31337
  rtime: 1520488877.415709329 (2018-03-08T06:01:17.415709)
  rtransid: 255755

Then make it read-only again:
gargamel:python-btrfs/examples# btrfs property set -ts /mnt/btrfs_bigbackup/DS1/Video_ro.20180220_21:03:41 ro true

But this didn't work:
ABORT: btrfs send -p /mnt/btrfs_pool1/Video_ro.20180220_21:03:41 Video_ro.20180308_07:50:06 |  btrfs receive
/mnt/btrfs_bigbackup/DS1//. failed
At subvol Video_ro.20180308_07:50:06
At snapshot Video_ro.20180308_07:50:06
ERROR: cannot find parent subvolume

You can see that with set_received_uuid.py, I set Received UUID to match UUID on the source:

gargamel:/mnt/btrfs_pool1# btrfs subvolume show /mnt/btrfs_bigbackup/DS1/Video_ro.20180220_21:03:41 DS1/Video_ro.20180220_21:03:41
        Name:                   Video_ro.20180220_21:03:41
        UUID:                   cb4f343c-5e79-7f49-adf0-7ce0b29f23b3
        Parent UUID:            0e220a4f-6426-4745-8399-0da0084f8b23 
        Received UUID:          2afc7a5e-107f-d54b-8929-197b80b70828 << changed this
        Creation time:          2018-02-20 21:13:36 -0800
        Subvolume ID:           94887
        Generation:             250689
        Gen at creation:        250689
        Parent ID:              89160
        Top level ID:           89160
        Flags:                  readonly
        Snapshot(s):

        Name:                   Video_ro.20180220_21:03:41
        UUID:                   2afc7a5e-107f-d54b-8929-197b80b70828
        Parent UUID:            e5ec5c1e-6b49-084e-8820-5a8cfaa1b089
        Received UUID:          0e220a4f-6426-4745-8399-0da0084f8b23
        Creation time:          2018-02-20 21:03:42 -0800
        Subvolume ID:           11228
        Generation:             4174
        Gen at creation:        4150
        Parent ID:              5
        Top level ID:           5
        Flags:                  readonly

Turns out however that because the source had a Parent UUID value too, I was actually supposed to set Received UUID on the destination to it:

gargamel:python-btrfs/examples# ./set_received_uuid.py 0e220a4f-6426-4745-8399-0da0084f8b23 313
37 1234.5678 /mnt/btrfs_bigbackup/DS1/Video_ro.20180220_21:03:41
Current subvolume information:
  subvol_id: 94887
  received_uuid: 2afc7a5e-107f-d54b-8929-197b80b70828
  stime: 1234.5678 (1970-01-01T00:20:34.567800)
  stransid: 31337
  rtime: 1520488877.415709329 (2018-03-08T06:01:17.415709)
  rtransid: 255755

Setting received subvolume...

Resulting subvolume information:
  subvol_id: 94887
  received_uuid: 0e220a4f-6426-4745-8399-0da0084f8b23
  stime: 1234.5678 (1970-01-01T00:20:34.567800)
  stransid: 31337
  rtime: 1520537034.890253770 (2018-03-08T19:23:54.890254)
  rtransid: 256119

gargamel:python-btrfs/examples# btrfs property set -ts /mnt/btrfs_bigbackup/DS1/Video_ro.201802 20_21:03:41 ro true

After this, I was able to re-start my btrfs send/receive and /mnt/btrfs_bigbackup/DS1/Video_ro.201802 20_21:03:41 was properly accepted as a destination. Yeah!