[PATCH RFC 0/6] spec: Decompose the daemon subpackage

[Daniel P. Berrangé]

On Wed, Nov 23, 2022 at 04:11:49PM -0700, Jim Fehlig wrote:
> Currently it is not possible to install a modular daemon subpackage without
> also installing the monolithic daemon
> 
> https://listman.redhat.com/archives/libvir-list/2022-September/234554.html
> 
> This series is an initial attempt at moving common daemons, utilities, and
> files from the daemon subpackage to a new daemon-core subpackage. The
> monolithic and modular daemons can then depend on the new subpackage.
> 
> libvirt-guests is moved to a new libvirt-guests subpackage, which is
> recommended by the daemon subpackage to provide smoother upgrade.
> 
> I've likely overlooked several items, but before continuing down this
> path too far I first wanted to gauge interest and see if this work is
> worth pursuing. If so, any comments on the RFC are appreciated!

With this refactoring the two big questions

 - What is the desired end state
 - Can we ensure a clean upgrade path

Let me ignore everything except the QEMU driver and the nodedev driver,
for sake of illustration.

Today we've got a few install approaches recommended

 - Ask for 'libvirt', which gives you

     - libvirt-daemon
     - libvirt-daemon-driver-qemu
     - libvirt-daemon-driver-nodedev

   All the libvirt pieces, but not the hypervisor itself


 - Ask for 'libvirt-daemon-kvm', which also gives you
 
     - libvirt-daemon
     - libvirt-daemon-driver-qemu
     - libvirt-daemon-driver-nodedev
     - qemu-kvm

   All the recommended libvirt pieces for QEMU, including
   the hypervisor itself


 - Ask for 'libvirt-daemon-driver-qemu', 'libvirt-daemon-driver-nodedev',
   which also gives you

     - libvirt-daemon

   The bare minimum libvirt pieces, but not the hypervisor itself


In terms of package contents

  - libvirt-daemon-driver-qemu

     /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so
     /usr/sbin/virtqemud

  - libvirt-daemon

     /usr/sbin/libvirtd
     /usr/sbin/virtlogd
     /usr/sbin/virtlockd
     /usr/sbin/virtproxyd


Our goal is the ability to install only the module daemon, without
libvirtd. This implies that we need to cut the dependency from
libvirt-daemon-driver-qemu, to libvirt-daemon.

I didn't do that originally because it would break apps that
installed libvirt-daemon-driver-qemu, expecting to get libvirtd.
We also needed it for the virtlogd/virtproxyd dep.

That decision, however, was made when libvirtd was still the
default active daemon.  Since we changed the systemd presets
in Fedora/RHEL to activate modular daemons, we don't need the
deps to pull in libvirtd by default.

We do not want to force virlockd as that's an opt-in feature,
and also don't want to force virtproxyd as that's only needed
for back compat with old remote libvirt clients, or for exposing
over TCP. 

virtlogd is more difficult, it is possible to turn that off
and if people do that they might prefer not to have it installed.
Or they may want to use it, but have it installed in a different
container from virtqemud. So on balance I thin we need to sever
the dependancy there too.

So I'd say we need to have

  - libvirt-daemon-lock
  
      /usr/sbin/virtlockd

  - libvirt-daemon-log
  
      /usr/sbin/virtlogd

  - libvirt-daemon-proxy
  
      /usr/sbin/virtproxyd

Probably a 'libvirt-daemon-plugin-lockd'  for the lock-driver/lockd.so
as that really ought to be  an optional component too.

A 'libvirt-daemon-client' package for 'virt-admin'

The libvirt-daemon package would need to hold

     /usr/sbin/libvirtd

and would also need dependencies for the upgrade path on

    libvirt-daemon-lock
    libvirt-daemon-log
    libvirt-daemon-proxy
    libvirt-daemon-pugin-lockd
    libvirt-daemon-client

I'm not sure if we'll still need a 'libvirt-daemon-core' too as your
patches suggest, for some of the common files, or if they all end up
in one of the other sub-RPMs above.

The libvirt-daemon-driver-XXX packages would then have *no* dependency
on anything. If you are asking for libvirt-daemon-driver-XXXX packages
of any kind, you're responsible for pickin the exact set of pieces you
want to have present.

Installing 'libvirt-daemon' will give you libvirtd, virtproxyd, virtlockd
etc, and you can ask for libvirt-daemon-driver-XXX on top.

The 'libvirt-daemon-kvm' would give you the sensible set of pieces,
*not* included libvirt-daemon any more though on distro versions which
have switched to module daemons.

The only thing we can't achieve this way is to install libvirtd and
QEMU, without having the module daemons present. I'm not sure that
matters though, if we aim to discontinue shipping libvirtd long term.

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|