Re: [Libguestfs] missing btrfs subvol support

Richard W.M. Jones
Thu, 10 Sep 2015 15:10:30 -0000

On Wed, Sep 09, 2015 at 07:14:05PM +0200, Olaf Hering
wrote:
> On Fri, Oct 10, Olaf Hering wrote:
>
> > Is btrfs subvol support failing just for me?
>
>
> This is an old thread, and it seems the underlying bug is not fixed
> because guestfs takes the wrong approach, IMO.
>
> >From how I understand btrfs, it has the concept of subvolumes. Each one
> is an entry point for a separate filesystem. In addition to that it has
> a default subvol which is used if no specific subvolume is specified.
> This turns the whole btrfs partition (or assembled blockdevice) into a
> container of individual filesystems.
>
> But guestfs, as far as I understand it, just mounts the btrfs filesystem
> with the default subvolume and ends up somewhere. Then it tries to make
> sense of the other subvolumes based on info from a /etc/fstab, which may
> or may not exist.  This looks like the wrong approach.
>
> Shouldnt it instead handle the whole thing as a container, just as it
> does for an individual disk? First do something like mount subvolid=0,
> poke around there and collect the items (sub list -a). Then use all this
> info to see which one might be one of the many root filesystems?

Matt?

Rich.

--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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