Re: empty directory from previous subvolume in a snapshot is not sent|received

[Andrei Borzenkov <arvidjaar@gmail.com>]

On 22.06.2023 16:34, Christoph Anton Mitterer wrote:
> Hey.
> 
> Not sure whether this is a bug or expected.
> 
> On my btrfs I have subvolumes like:
>    data/
>    2023-06-21/
> where e.g. data/ contains the root filesystem and 2023-06-21/ is a ro-
> snapshot thereof.
> 
> 
> When I created 2023-06-21/ from data/, the latter contained another
> (rw-)subvolume data/pictures/, which I've deleted (actually: moved out
> the files back to data/ and rmdir-ed the now empty subvol... or maybe I
> did btrfs subvolume delete - not sure anymore) again after creating the
> snapshot.
> 
> 
> Now 2023-06-21/ contains an empty (non-subvolume) 2023-06-21/pictures/,
> which is expected.
> 
> 
> Today I've send|received 2023-06-21/ to another btrfs (at that point,
> the original data/pictures/ subvolume was already gone), and diff -qr -
> -no-dereference-ed the two afterwards.
> 
> Outcome (apart from "differing" files/sockets/block/char special files)
> is that the target doesn't contain the empty pictures/ dir.
> 
> 
> Not a big problem for me,... but is this expected or some kind of
> strange bug?
> 
> 

I think it is expected. btrfs does not support either recursive 
snapshots or recursive send so "btrfs send" skips directory entry that 
points to subvolume root.