Re: [PATCH 4/4] vl: Prioritize realizations of devices

[Peter Xu]

On Thu, Sep 02, 2021 at 04:57:04PM +0200, Markus Armbruster wrote:
> Peter Xu <peterx@redhat.com> writes:
> 
> > Hi, Dan,
> >
> > On Thu, Sep 02, 2021 at 02:53:00PM +0100, Daniel P. Berrangé wrote:
> >> The correct ordering of devices/backends is generally pretty obvious
> >> for libvirt to determine. Most of the problems we've had related to
> >> ordering are on the QEMU side, because the ARGV given to QEMU made
> >> correct sense if parsed left-to-right, but QEMU didn't actually process
> >> them in that order. We've patched QEMU to hack around its inability to
> >> honour the CLI order repeatedly.
> >
> > Is there a pointer to the problem?
> 
> Just an example:
> 
> 9ea18ed25a "vl: Fix -drive / -blockdev persistent reservation management
> cda4aa9a5a "vl: Create block backends before setting machine properties"

Thanks, same to Dan.

> 
> >> Being completely self-ordering on the QEMU side using a topological
> >> sort would be neat from a conceptual purity POV, but that is quite a
> >> challenge to implement and I'm not convinced it is worth it, compared
> >> to other problems we want to spend time on.
> >
> > I just noticed there can also be dependency between the buses; that cannot 
> > be
> > fixed by ordering of classes indeed as either proposed in this series, or
> > introduce a new priority.
> 
> --verbose?

Please ignore it - I just started to realize what kind of a rabbit hole I'm
digging, and I am already prepared to run away. :)

-- 
Peter Xu