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Re: [Qemu-devel] How to best handle the reoccurring of rom changes break

From: Christian Ehrhardt
Subject: Re: [Qemu-devel] How to best handle the reoccurring of rom changes breaking cross version migrations?
Date: Thu, 2 Nov 2017 16:14:06 +0100

Ping - since there wasn't any reply so far - any best practices one could

Let me add a TL;DR:
- bump of ipxe rom versions change the size of virtio-net-pci.rom
- that breaks on migration "Length mismatch"

I'd guess the size of that rom has to be fixed up on the fly, but if that
is really ok and how/where is the question.

Also to +1 on bad things for today - I made this a cross post to libvirt in
case there is one that has done that in the past.

On Mon, Aug 28, 2017 at 4:36 PM, Christian Ehrhardt <
address@hidden> wrote:

> Hi,
> migration issues due to rom changes seem to occur over and over in past
> years [1], [2],[3],[4],[5].
> From the past I know several workarounds (like just truncating to the
> bigger size) but all have various deficiencies.
> But OTOH rom's will always change due to fixes in them. And recently I
> found one such change [6] that affects the next Ubuntu release and wonder
> what the ?right?, well lets say best way to fix it would be.
> Current issue:
> Length mismatch: 0000:00:03.0/virtio-net-pci.rom: 0x40000 in != 0x80000:
> Invalid argument
> Due to efi-virtio.rom growing over 256k due to an update to a newer ipxe
> from upstream.
> I beg your pardon (for not being educated enough on this yet), but I want
> to avoid to go a route that is fixing it in a sub-optimal way and ask for
> some guidance. There might be better ways in the modern qemu of today than
> there were in the past.
> TL;DR I look for the best way (if any) to declare in the new qemu: "I know
> that the old size was smaller, let me fix that up on migration".
> I'll try on my own as I expect the machine type structures/mechanisms (and
> we have Ubuntu specific types that could encapsulate the rom status from
> the ipxe package to be coupled with the type) have all that is needed.
> Yet me almost randomly trying around there surely isn't the best way to go
> - so if there is some existing case or a short hint at what in there might
> be the best way to fixup a changed rom size on a migration I'd be very
> happy to hear about that.
> [1]: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1536331
> [2]: https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg01881.html
> [3]: https://bugzilla.redhat.com/show_bug.cgi?id=1293566
> [4]: https://bugzilla.redhat.com/show_bug.cgi?id=1090093
> [5]: https://forge.univention.org/bugzilla/show_bug.cgi?id=38877
> [6]: https://bugs.launchpad.net/ubuntu/+source/ipxe/+bug/1713490
> P.S: As everybody else I don't mind so much on reverse migration to older
> releases
> --
> Christian Ehrhardt
> Software Engineer, Ubuntu Server
> Canonical Ltd

Christian Ehrhardt
Software Engineer, Ubuntu Server
Canonical Ltd

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