Continuing on making the VM ID suggestion strategy configurable

[Severen Redwood]

Hi everyone,

Something I've been running into with PVE is that VM IDs may be re-used
and that the UI will in fact suggest the smallest available ID (via the
`/cluster/nextid` endpoint), regardless of whether that ID has
previously been used or not. This can cause issues with PBS as it keys
backups by VM ID, which is detailed on this Bugzilla issue [1], so for
brevity I won't replicate the discussion here.

There's a patch series [2] from a few months ago which addresses this by
making the VM ID suggestion strategy configurable with the following
options:

1. Use the smallest ID that is not currently in use (current behaviour).
2. Use one greater than the largest ID in use.
3. Use the smallest ID that is neither currently nor previously in use.

In particular, option 3 is the one that would best solve the problem for
me.

However, the patches are stuck on some unresolved feedback and the
author (CC'd in) seems to have either paused or abandoned work on the
feature. For this reason, I'm interested in picking up where they left
off to get the feature to an acceptable state. Is this OK? And how
feasible is it that this feature would ultimately be accepted? At the
moment, the only nontrivial issue raised with the patches seems to be
regarding where the list of previously used VM IDs should be stored,
which I believe should be resolvable.

Thanks,
Severen

[1]: https://bugzilla.proxmox.com/show_bug.cgi?id=4369#c13
[2]: https://lore.proxmox.com/pve-devel/D1RYIAHXBOIH.RM5K01KGND9T@proxmox.com/t/

P.S. This is my first time using a mailing list, so please let me know
about any inadvertent breaches of etiquette :)