problem with noatime flag

Thanks for your bugreport.

I added some code into trunk now that will detect noatime and simply bail out for now. We need a more clever way of detecting the snapshots age in this case. The code must ensure that it detects when a snapshot was booted last, not when it was taken.

This bug was fixed in the package apt-btrfs-snapshot - 0.3

---------------
apt-btrfs-snapshot (0.3) quantal; urgency=low

  [ Michael Vogt ]
  * apt_btrfs_snapshot.py, test/test_apt_btrfs_snapshot.py:
    - disable "delete-older-than" command if noatime is in use on
      the snapshot fs (LP: #833980)
  * merge lp:~brian-murray/apt-btrfs-snapshot/fix-vcs/, many thanks!
  * apt_btrfs_snapshot.py:
    - be even more robust against invalid fstab entries
      (LP: #873411 comment #7)
  * test/test_pyflakes.py:
    - add test that ensures that its pyflakes clean

  [ Dmitrijs Ledkovs ]
  * apt_btrfs_snapshot.py, apt-btrfs-snapshot:
    - port to python3
  * apt_btrfs_snapshot.py:
    - fix pyflakes warning use 'AptBtrfsNotSupportedError' instead of
      undefined name 'AptBtrfsSnapshotNotSupportedError'
  * test/test_apt_btrfs_snapshot.py:
    - remove unused imports 'LowLevelCommands' and 'apt_btrfs_snapshot'
    - mock sys.stdout and sys.stderr to avoid confusing and spurious output
    - mock /sbin/btrfs to allow running unit-tests without btrfs-tools
  * debian/rules:
    - build with supported versions of python2 and python3
    - run unittests at build time, honoring nocheck
  * debian/control:
    - adjust dependencies for python3 support
    - bump standards version to 3.9.3
 -- Michael Vogt <email address hidden> Tue, 12 Jun 2012 12:06:31 +0200

I'm coming from question 263994 and I was wondering why apt-btrfs-snapshot denies to work on a fs with noatime.
Initially I had expected mtime should be enough.

> The code must ensure that it detects when a snapshot was booted last, not when it was taken.
Can you elaborate why it is not enough to simply look at the age of the snapshot?

Can you please add a comment on why the atime check is necessary?

@benbuntu, @darkdragon-001 see here: http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/vivid/apt-btrfs-snapshot/vivid/view/head:/apt_btrfs_snapshot.py#L194

Author uses atime of /etc/fstab inside the snapshot to know it's creation time.
- Simplest fix would be to exclude `noatime` from mount options list, which read from /etc/fstab.
- Another way is to create some empty file in filesystem root, lets say `apt-btrfs-snapshot` and use it's ctime for checking. After snapshot created, that file should be deleted.

I think it is better to parse the snapshot name, since it includes the creation time anyway. Feel free to review my changes: https://code.launchpad.net/~darkdragon-001/apt-btrfs-snapshot/trunk