Re: [Qemu-stable] [PATCH 1/4] configure: Add --enable-migration-from-qemu-kvm

[Paolo Bonzini]

Il 20/02/2013 21:26, Anthony Liguori ha scritto:
> Cole Robinson <address@hidden> writes:
> 
>> This switch will turn on all the migration compat bits needed to
>> perform migration from qemu-kvm to qemu. It's just a stub for now.
>>
>> This compat will break incoming migration from qemu < 1.3, but for
>> distros where qemu-kvm was the only shipped package for years it's
>> not a big loss (and I don't know any way to avoid it).
>>
>> Signed-off-by: Cole Robinson <address@hidden>
> 
> This can't be a build time option.  It's ugly and just reintroduces a fork.

It is not a fork; it does not change the migration format of QEMU
itself, only the parsing of old VMState versions.  The importance of the
fork will dwindle over time, as the distros EOL the releases that used
qemu-kvm.

> I assume the issue with making it a run time option is that libvirt
> would need to be updated?

You cannot update libvirt, because whether to pass the flag or not
depends on the _source_ QEMU, which may be an ancient version we cannot
add any patch to.

> Why can't qemu-kvm be a script wrapper that
> passes a fixed flag?

See Cole's answer; qemu-system-* also used to be built from qemu-kvm
sources in Fedora.

Paolo