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

[Markus Armbruster]

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"

>> 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?