On Mi, 27.06.18 15:09, Ignaz Forster ([email protected]) wrote: > Am 27.06.2018 um 13:39 schrieb Lennart Poettering: > > On Mi, 27.06.18 13:02, Ignaz Forster ([email protected]) wrote: > > > > > Hello, > > > > > > when using systemd-tmpfiles' feature to create subvolumes it will always > > > create the new subvolume as a child of the subvolume of the given path. > > > This > > > however may not always be the expected parent, especially when using btrfs > > > snapshots to switch between various system states. > > > > > > Example layout: > > > =============== > > > > > > Let's assume the following subvolume layout (a simplified openSUSE > > > layout): > > > > > > ID parent top level path > > > -- ------ --------- ---- > > > 257 5 5 <FS_TREE>/@ > > > 258 257 257 <FS_TREE>/@/var > > > 259 257 257 <FS_TREE>/@/.snapshots/1/snapshot > > > 260 257 257 <FS_TREE>/@/.snapshots/2/snapshot > > > 261 257 257 <FS_TREE>/@/.snapshots/3/snapshot > > > > > > A corresponding /etc/fstab could look like this: > > > > > > /dev/sdx / btrfs defaults 0 0 > > > /dev/sdx /var btrfs subvol=@/var 0 0 > > > > > > with the default btrfs subvolume set to "261". > > > The third snapshot would thus be the root file system, with /var mounted > > > on > > > top of it. > > > > > > > > > The problem: > > > ============ > > > > > > Creating "/var/test" would create a new entry like > > > 262 258 258 @/var/test > > > as expected. > > > However creating "/opt" would create an entry similar to the following: > > > 263 261 261 @/.snapshots/3/snapshot/opt > > > > > > This is not good, as two things will happen now: > > > * When changing the snapshot (e.g. by reverting back to an old snapshot or > > > creating a new one) /opt won't be visible any more (without manually > > > mounting it), as it is not nested into the existing structure any more > > > * The third snapshot cannot be deleted without removing the > > > subvolume first > > > > I am not sure I follow here fully. but isn't this just a shortcoming because > > you are not doing recursive snapshots? why not just fix that? > > With "recursive snapshots" I assume you mean putting the snapshot below the > original root file system?
By recursive snaphots I really mean recursive snapshots, i.e. if you have a subvolume called `/foobar` and there's a subvolume below it called `/foobar/var`, and you'd make a snapshot of `/foobar` and call it `/foobar2`, then this would implicitly also have the effect of snapshotting `/foobar/var` and calling it `/foobar2/var`, so that each snapshot is always "complete". Lennart -- Lennart Poettering, Red Hat _______________________________________________ systemd-devel mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/systemd-devel
