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Re: d-i rescue with btrfs rootfs (was: rescue_1.102_source.changes ACCEPTED into unstable)



Sorry for accidentally sending from @gmail rather than @debian.org (I'm
still debugging my notmuch setup).

Pascal Hambourg <pascal@plouf.fr.eu.org> writes:

> On 18/05/2025 at 01:00, Nicholas D Steeves wrote:
>> Pascal Hambourg <pascal@plouf.fr.eu.org> writes:
>>>
>>> However it may not work with a system installed from Debian live with
>>> Calamares which appears to set a different btrfs subvolume layout (see
>>> #1104552). (...) so would it be desirable to add
>>> (trivial) support for this case in d-i RC2 ?
>
> Note: this is a one-liner patch. I am ready to open a MR.
>
>> I'm CCing Debian's Calamares maintainer, because I think this is an
>> upstream Calamares bug.  I hypothesise that the nature of the Calamares
>> bug is that upstream assumes Ubuntu-style subvolume layout that we never
>> intended to support in Debian.
>
> Thank you, it would be good to know whether this layout comes from 
> Calamares upstream, the Debian package or Debian Live configuration.

I cloned everything that seemed relevant, and fairly quickly searched
and scanned, and what I found was that Calamares' btrfs layout can be
configured with a "mount.conf", but it sounds like only if one defaults
to btrfs.  We default to ext4, so it falls back to hard-coded.  As I
hypothesized, upstream Calamares appears to hard-code Ubuntu-style
layout

    src/modules/mount/main.py
    143:        btrfs_subvolumes = [dict(mountPoint="/", subvolume="/@"), dict(mountPoint="/home",     subvolume="/@home")]

>> In case anyone missed the following reply to that bug:
>> 
>>> Have you been able to track down those discussions where we decided on
>>> @rootfs?
>
> To be honest, I am not so interested in past discussions. I am more 
> concerned about the current inconsistent state and interested in 
> aligning partman and Calamares btrfs layouts in one way or the other and 
> having rescue mode support both layouts in the meantime.

TLDR: By doing this we would be supporting the Ubuntu layout becoming a
defacto bug-for-bug standard; this wastes the time and effort of
everyone who has already implemented flexible, configurable software,
and rewards supporting static "@, @home" systems to the exclusion of all
else.  That's wrong, unjust, and not what Debian is supposed to do.

If the priority is the inconsistent state, lets:

  1. Fix Calamares (#1104552 reassigned; MR submitted)
  2. Decide if we're going to share the "@home" namespace with Ubuntu
  and SUSE.  If yes, and the priority is consistency, then we need to
  start creating and mounting "@home" (which will sometimes already
  exist).
  3. Convert bugged installs to standard installs (this is easy, safe, and
  revertible)


Cheers,
Nicholas

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