Enable LVM autoextend

[marmarek]

Qubes OS version
R4.0

Affected component(s) or functionality
lvm, installer

Brief summary
Installer (anaconda) leaves some space not allocated (~20% now, previously less). This is supposed to be used by LVM autoextend to automatically enlarge data or metadata volumes according to the needs. But autoextend is disabled.

To Reproduce
Steps to reproduce the behavior:
1. Install Qubes 4.0
2. Check LVM pool size and settings
3. See ~20% not allocated, but thin_pool_autoextend_threshold in /etc/lvm/lvm.conf set to 100 (effectively disabling the feature)

Expected behavior
When free space is left, autoextend should be enabled to make use of it.

Actual behavior
Autoextend not enabled.

Additional context
This is yet another countermeasure for filling up metadata volume.

Relevant documentation you've consulted
#3243

Related, non-duplicate issues
A list of links to other bug reports, feature requests, or tasks in the qubes-issues tracker (or "none" if you didn't find any). Do not describe any other unreported bugs, features, or tasks here.

[marmarek]

This one is annoying: lvm config is quite unfriendly to modify via packages - there is no conf.d, and lvm complains about duplicated options (so appending at the end to override earlier value results in a warning)

[DemiMarie]

This one is annoying: lvm config is quite unfriendly to modify via packages - there is no conf.d, and lvm complains about duplicated options (so appending at the end to override earlier value results in a warning)

sed -Ei?

[marmarek]

I'd like to avoid conflicting/overriding user changes as much as possible. This parameter does make sense for the user to change (for extremely large disks for example). I'd like to at least insert a comment saying what user needs to do, to override automatic value (which would be re-added at subsequent update).

[andrewdavidwong]

Should this have priority P: blocker since it's included in https://github.com/QubesOS/qubes-issues/projects/6?

[DemiMarie]

I'd like to avoid conflicting/overriding user changes as much as possible. This parameter does make sense for the user to change (for extremely large disks for example). I'd like to at least insert a comment saying what user needs to do, to override automatic value (which would be re-added at subsequent update).

Should be doable. What about modifying it if it is commented out or set to 100, and leaving alone otherwise?