Re: [PATCH] qemu: Switch to virtio-scsi on ARM
On Wed, Jul 02, 2025 at 02:01:07PM -0600, Jim Fehlig wrote:
On 7/2/25 10:11, Andrea Bolognani wrote:
> On Thu, Jun 26, 2025 at 03:29:58PM -0600, Jim Fehlig via Devel wrote:
> > However, I do understand this
> > change could break existing ARM VM configurations containing a SCSI
> > controller without a model specification. One could also argue the pain
> > inflicted is tolerable :-).
>
> I don't think this should necessarily be a concern.
>
> Unlike, say, USB controllers, where in some cases you could end up
> with no model recorded in the XML, for SCSI controllers we always
> either figure out a suitable model or fail defining the domain
> altogether.
>
> So changing the default here should have no impact on existing
> domains and simply improve things for newly-created ones.
I was thinking of transient domains with no explicit model defined. Prior to
this change they would get lsilogic, afterwards virtio-scsi. In practice I
doubt there are (m)any such domains in existence.
I don't use transient domains so I might be missing something, but my
understanding is that by definition they can't really expect ABI
stability to the extent regular domains can since every creation
event is independent from the previous ones from libvirt's
perspective.
We have a bunch of cases in which we do things differently for
existing domains compared to newly-created ones, specifically in
order to preserve ABI stability, and IIUC transient domains will
always get the latter behavior.
So I think we're still in the clear.
--
Andrea Bolognani / Red Hat / Virtualization