bug#29674: Ceph creates Btrfs subvolumes on Btrfs during tests.

[Rutger Helling <rhelling@mykolab.com>]

Actually, I just tested it with the following:

$ cd /tmp
$ sudo -s -u guixbuilder01
bash-4.4$ guix environment -C --ad-hoc btrfs-progs
guixbuilder01@guixsd /tmp [env]#  btrfs subvol create test-snapshot
Create subvolume './test-snapshot'
guixbuilder01@guixsd /tmp [env]#  btrfs subvol del test-snapshot
Delete subvolume (no-commit): '/tmp/test-snapshot'
ERROR: cannot delete '/tmp/test-snapshot': Operation not permitted
guixbuilder01@guixsd /tmp [env]# exit
exit
bash-4.4$ guix environment -C --ad-hoc coreutils
guixbuilder01@guixsd /tmp [env]#  rm -rfv test-snapshot/
rm: cannot remove 'test-snapshot/': Operation not permitted
guixbuilder01@guixsd /tmp [env]#  rmdir  -v test-snapshot/
rmdir: removing directory, 'test-snapshot/'
rmdir: failed to remove 'test-snapshot/': Operation not permitted
guixbuilder01@guixsd /tmp [env]#

On 2017-12-12 14:10, Rutger Helling wrote:

> Hi Ludo,
> 
> I'll try building again later (could be a while, Ceph takes a really 
> long time to build), but I highly doubt that that's the case.
> Btrfs subvolumes cannot be deleted with tools such as rm/rmdir, even as 
> root. You have to run 'btrfs subvolume delete /subvolume' as root.
> Although a regular user may create subvolumes, they cannot delete it 
> (unless the USER_SUBVOL_RM_ALLOWED mount option is on).
> Since the building is done as a guixbuilder user, I don't see how that 
> would work.
> And even if it did, if a build failed for example you'd still be left 
> with a bunch of subvolumes in /tmp that can only be deleted as root.
> 
> On 2017-12-12 13:52, ludo@gnu.org wrote:
> 
> Hi Rutger,
> 
> Rutger Helling <rhelling@mykolab.com> skribis:
> 
> I was surprised to learn that Ceph creates Btrfs subvolumes during its
> tests.
> This is problematic because on Btrfs regular users can create
> subvolumes, but they cannot delete them.
> This means I had to manually delete the following subvolumes as root:
> 
> ID 1744 gen 819598 top level 257 path
> tmp/guix-build-ceph-12.0.2.drv-0/td/t-7201/dev/osd0/current
> ID 1745 gen 819598 top level 257 path
> tmp/guix-build-ceph-12.0.2.drv-0/td/t-7201/dev/osd0/snap_1
> Does that mean that wiping out /tmp/guix-build-ceph-*, as happens when
> build finishes, isn't enough to get rid of those volumes?
> 
> Ludo'.