[systemd-devel] the need for a discoverable sub-volumes specification

[Chris Murphy]

Lennart most recently (about a year ago) wrote on this in a mostly
unrelated Fedora devel@ thread. I've found the following relevant
excerpts and provide the source URL as well.

BTW, we once upon a time added a TODO list item of adding a btrfs
generator to systemd, similar to the existing GPT generator: it would
look at the subvolumes of the root btrfs fs, and then try to mount
stuff it finds if it follows a certain naming scheme.
https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/M756KVDNY65VONU3GA5CSXB4LBJD3ZIW/


All I am asking for is to make this simple and robust and forward
looking enough so that we can later add something like the generator I
proposed without having to rerrange anything. i.e. make the most basic
stuff self-describing now, even if the automatic discovering/mounting
of other subvols doesn't happen today, or even automatic snapshotting.

By doing that correctly now, you can easily extend things later
incrementally without breaking stuff, just by *adding* stuff. And you
gain immediate compat with "systemd-nspawn --image=" right-away as the
basic minimum, which already is great.
https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/JB2PMFPPRS4YII3Q4BMHW3V33DM2MT44/


We manage to name RPMs with versions, epochs, archs and so on, I doubt
we need much more for naming subvolumes to auto-assemble.
https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/VBVFQOG5EYI73CGFVCLMGX72IZUCQEYG/


--
Chris Murphy