Re: [Libguestfs] missing btrfs subvol support

Olaf Hering
Wed, 09 Sep 2015 17:14:05 -0000

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?


Olaf