Fix bug in fstab layout generation

This fixes a bug in our fstab layout generation,
currently we fail to generate the complete fstab layout, so /etc/fstab
in any newly deployed or upgraded baserocks contains just:

    # Morph default system layout
    UUID=<uuid>  / btrfs defaults,rw,noatime 0 1

This is actually a pretty bad problem because it breaks
system-version-manager, since systemd creates a btrfs subvolume and
mounts it to /var/lib/machines if /var/lib/machines doesn't already
exist[1]. As a result system-version-manager when asked to remove an image
will fail to do so, since it will fail to remove the /run subvolume
because of the subvolume created at /run/var/lib/machines. The result is
a partially removed image that cannot be removed with system-version-manager.

The fstab layout we use currently:

    UUID=<uuid>  / btrfs defaults,rw,noatime 0 1
    UUID=<uuid>  /var  btrfs subvol=/state/var,defaults,rw,noatime 0 2
    UUID=<uuid>  /opt  btrfs subvol=/state/opt,defaults,rw,noatime 0 2
    UUID=<uuid>  /srv  btrfs subvol=/state/srv,defaults,rw,noatime 0 2
    UUID=<uuid>  /root  btrfs subvol=/state/root,defaults,rw,noatime 0 2
    UUID=<uuid>  /home  btrfs subvol=/state/home,defaults,rw,noatime 0 2

ensures that anything created under /var goes into a shared /state/var subvolume,
so when systemd creates its 'machines' subvolume it will be under state/
which doesn't cause any problems when we try to remove a system.

To reproduce, deploy an upgrade to your machine, reboot into the upgraded
system, when you cat /etc/fstab you should see only one entry, mounting /.
Now switch back to the previous image with,

    system-version-manager set-default <previous image name>
    reboot

remove the newly deployed image with,

    system-version-manager remove <upgraded image name>

after some time this will fail with an error message similar to this:

    Removing system: faultylayout
    Delete subvolume (no-commit): '/tmp/tmp1gdIL2/systems/faultylayout/run'
    ERROR: cannot delete '/tmp/tmp1gdIL2/systems/faultylayout/run' - Directory not empty
    Delete subvolume (no-commit): '/tmp/tmp1gdIL2/systems/faultylayout/orig'
    Traceback (most recent call last):
      File "/usr/bin/system-version-manager", line 421, in <module>
        SystemVersionManager(sys.argv, mount_dir).run()
      File "/usr/bin/system-version-manager", line 401, in run
        self.cmd_remove(args.system_name)
      File "/usr/bin/system-version-manager", line 363, in cmd_remove
        shutil.rmtree(system_root)
      File "/usr/lib/python2.7/shutil.py", line 247, in rmtree
        rmtree(fullname, ignore_errors, onerror)
      File "/usr/lib/python2.7/shutil.py", line 247, in rmtree
        rmtree(fullname, ignore_errors, onerror)
      File "/usr/lib/python2.7/shutil.py", line 247, in rmtree
        rmtree(fullname, ignore_errors, onerror)
      File "/usr/lib/python2.7/shutil.py", line 247, in rmtree
        rmtree(fullname, ignore_errors, onerror)
      File "/usr/lib/python2.7/shutil.py", line 256, in rmtree
        onerror(os.rmdir, path, sys.exc_info())
      File "/usr/lib/python2.7/shutil.py", line 254, in rmtree
        os.rmdir(path)
    OSError: [Errno 1] Operation not permitted: '/tmp/tmp1gdIL2/systems/faultylayout/run/var/lib/machines

[1]: http://cgit.freedesktop.org/systemd/systemd/commit/?id=113b3fc1a8061f4a24dd0db74e9a3cd0083b2251

Change-Id: I9c160d1fdd75fbbf9a3336d1ce35e4ce8ed7787d

1 files changed, 4 insertions, 3 deletions

diff --git a/extensions/writeexts.py b/extensions/writeexts.py
index de7c0f2e..f356a34a 100644
--- a/extensions/writeexts.py
+++ b/extensions/writeexts.py
@@ -606,10 +606,10 @@ class WriteExtension(Extension):
             fstab.add_line('%s  / btrfs defaults,rw,noatime 0 1' % root_device)
 
         # Add fstab entries for partitions
+        part_mountpoints = set()
         if device:
             mount_parts = set(p for p in device.partitionlist
                           if hasattr(p, 'mountpoint') and p.mountpoint != '/')
-            part_mountpoints = set(p.mountpoint for p in mount_parts)
             for part in mount_parts:
                 if part.mountpoint not in existing_mounts:
                     # Get filesystem UUID
@@ -621,17 +621,18 @@ class WriteExtension(Extension):
                     fstab.add_line('UUID=%s  %s %s defaults,rw,noatime '
                                    '0 2' % (part_uuid, part.mountpoint,
                                             part.filesystem))
+                    part_mountpoints.add(part.mountpoint)
                 else:
                     self.status(msg='WARNING: an entry already exists in '
                                     'fstab for %s partition, skipping' %
                                     part.mountpoint)
 
         # Add entries for state dirs
+        all_mountpoints = set(existing_mounts.keys()) | part_mountpoints
         state_dirs_to_create = set()
         for state_dir in shared_state_dirs:
             mp = '/' + state_dir
-            if (mp not in existing_mounts and
-                    (device and mp not in part_mountpoints)):
+            if mp not in all_mountpoints:
                 state_dirs_to_create.add(state_dir)
                 state_subvol = os.path.join('/state', state_dir)
                 fstab.add_line(