Re: [Qemu-devel] [PATCH 3/4] virtio: modify savevm to have a stable wire format

[Anthony Liguori <anthony@codemonkey.ws>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> Il 14/12/2012 01:57, Rusty Russell ha scritto:
>> With the new code we only need the head from that structure.
>
> We also need to do again all validation of the elements if we fetch it
> back from the data.  Sometimes the parsed data is saved elsewhere (e.g.
> in a SCSIRequest struct that is serialized by the SCSI subsystem) and
> that data may be inconsistent with whatever you read from guest memory.
>  It's a can of worms.
>
>>> I'm certainly in favor of cleaning up the savevm format and probably
>>> leaving the existing load/save functions as-is for legacy purposes.
>>> I'll leave that as an exercise for someone else though :-)
>> 
>> What is the rule about new versions?  Can we introduce a new save
>> version at any time, or only at major qemu version changes?
>
> Any time, but we provide a backwards-compatible loader for older
> versions.

Well..  if we can avoid bumping the version, we should.  Bumping the
version breaks migration from new -> old so it's preferrable that we
don't do it unless it's absolutely required.

Regards,

Anthony Liguori

>
> Paolo