Recursive subvolume snapshots and deletion?

Recursive subvolume snapshots and deletion?

[Lennart Poettering]

Heya!

So what's the story on recursive btrfs snapshotting and snapshot
removal? Since a while systemd has now by default creating btrfs
subvolumes for /var/lib/machines for example. Now, if that code is run
inside a container, and the container itself already is stored in a
subvolume we end up with a subvolume inside a subvolume, which
currently breaks snapshotting and deletion of the outer container
subvolume.

What's the plan regarding recursive versions of the operations? Any
plan to add this? We could work around this in userspace, of course,
but it would not be atomic, and I'd much prefer if the kernel could do
this on its own!

Lennart

Re: Recursive subvolume snapshots and deletion?

[Chris Mason]

On Mon, Mar 23, 2015 at 12:57 AM, Lennart Poettering 
<mzerqung@0pointer.de> wrote:
> Heya!
> 
> So what's the story on recursive btrfs snapshotting and snapshot
> removal? Since a while systemd has now by default creating btrfs
> subvolumes for /var/lib/machines for example. Now, if that code is run
> inside a container, and the container itself already is stored in a
> subvolume we end up with a subvolume inside a subvolume, which
> currently breaks snapshotting and deletion of the outer container
> subvolume.
> 
> What's the plan regarding recursive versions of the operations? Any
> plan to add this? We could work around this in userspace, of course,
> but it would not be atomic, and I'd much prefer if the kernel could do
> this on its own!

Hi Lennart,

I've got a patch to btrfs-progs that can do the recursive snapshotting, 
let me clean it up and submit to Dave.  For recursive deletion I think 
the same method can be used.

-chris

Re: Recursive subvolume snapshots and deletion?

[Lennart Poettering]

On Mon, 23.03.15 08:36, Chris Mason (clm@fb.com) wrote:

> On Mon, Mar 23, 2015 at 12:57 AM, Lennart Poettering <mzerqung@0pointer.de>
> wrote:
> >Heya!
> >
> >So what's the story on recursive btrfs snapshotting and snapshot
> >removal? Since a while systemd has now by default creating btrfs
> >subvolumes for /var/lib/machines for example. Now, if that code is run
> >inside a container, and the container itself already is stored in a
> >subvolume we end up with a subvolume inside a subvolume, which
> >currently breaks snapshotting and deletion of the outer container
> >subvolume.
> >
> >What's the plan regarding recursive versions of the operations? Any
> >plan to add this? We could work around this in userspace, of course,
> >but it would not be atomic, and I'd much prefer if the kernel could do
> >this on its own!
> 
> Hi Lennart,
> 
> I've got a patch to btrfs-progs that can do the recursive snapshotting, let
> me clean it up and submit to Dave.  For recursive deletion I think the same
> method can be used.

OK, so this means you want this to be solved in userspace, hence in a
non-atomic fashion?

What precisely will your code do? Enumerate the subvolumes and simply
snapshot all subvolumes below the desired path? Or anything smarter?

Lennart

-- 
Lennart Poettering, Red Hat