Re: [Qemu-devel] Live migrate, inconsistent machine types - new machine type to fix?

[Paolo Bonzini]

Il 19/07/2014 09:10, Alex Bligh ha scritto:
>>> Looks like your source and destination machines have different
>>> iPXE ROMs.  This could be a packaging problem in your distro.
> 
> This is Ubuntu 12.04 to Ubuntu 14.04. I think the 14.04 one is
> correct, and don't want to run with a non-standard qemu there.

No, the old one is _always_ the correct one.

The pxe-* ROMs must be 128k, the efi-* ROMs must be 256k.  If distros do
not do that, they have a bug (and as you noticed it's not one that they
can easily work around, since now you have different releases with
different ROM sizes for the same machine types).

> Can I use a different ROM (e.g. the old one) with a command line
> option just for the migrated machines? Obviously when they reboot,
> they'l get a hardware change (which is fine).

Yes, "-global foo.romfile" on the destination QEMU.  You can just pass
an empty 128k file to the destination since ROM contents are migrated
properly, and hardware will only change when QEMU restarts.

Migration is extremely complex because you have to strike the right
balance between compatibility and maintainability.  Whether it works, it
depends on a lot of factors that vary per distro, and the only thing
that can keep it working is a lot of testing.

I don't know of any distro that actively tests migration except RHEL,
SLES.  I'm not sure about Debian.  Since there is no free-beer SLES,
you'd better switch to CentOS 7 than keeping Ubuntu 14.04.

Paolo