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

[Chris Murphy]

On Thu, Dec 30, 2021 at 3:59 PM Chris Murphy <lists at colorremedies.com> wrote:
>
> ZFS uses volume and user properties which we could probably mimic with
> xattr. I thought I asked about xattr instead of subvolume names at one
> point in the thread but I don't see it. So instead of using subvolume
> names, what about stuffing this information in xattr? My gut instinct
> is this is less transparent and user friendly, it requires more tools
> to know how to user to troubleshoot and fix, etc.

Separate from whether the obscurity of an xattr is a good idea or not,
read-only snapshots can't have xattr added, removed, or modified. We
can rename read-only snapshots, however.

While we could unset the ro property, that also wipes received UUID
used by send/receive. And while we could make an rw snapshot of the ro
snapshot, modify the xattr, then make an ro snapshot of the rw
snapshot, this alters the parent UUI also used by send/receive. So it
complicates send/receive workflows as a potential update mechanism, or
for backup/restore, for anything that tracks these UUIDs, e.g. btrbk.


-- 
Chris Murphy