Problem with applying incremental btrfs-send

Problem with applying incremental btrfs-send

[Harald Hoyer]

Hi,

maybe someone can enlighten me. I am doing btrfs send & receive with full
snapshots and incremental updates.

It basically looks like this:

vol-0 and vol-1 are full subvolume image sends.
inc-1 and inc-2 are incremental images with:
# btrfs send -f inc-1 -p vol vol'
# btrfs send -f inc-2 -p vol' vol''

Case A:

vol---send----> vol-0 --receive--> avol  --send&rec--> bvol
|-----send----> inc-1 --receive-->  |                   | <--receive-- inc-1
vol' -send----> vol-1              avol'               bvol'
|-----send----> inc-2 --receive-->  |                   | <--receive-- inc-2
vol''                              avol''              bvol''

which, works for bvol and which even works, if bvol is removed before inc-2 is
applied to bvol'.

Case B:

vol---send----> vol-0 --receive--> avol
|-----send----> inc-1 --receive-->  |
vol' -send----> vol-1              avol' --send&rec--> bvol'
|-----send----> inc-2 --receive-->  |                   | <--receive-- inc-2
vol''                              avol''              ERROR


trying to apply inc-2 to bvol' fails with:

ERROR: could not find parent subvolume

What's the problem here?