Re: [Qemu-devel] [PATCH] virtio: verify that all outstanding buffers are flushed (was Re: vmstate conversion for virtio?)

[Rusty Russell <rusty@rustcorp.com.au>]

Anthony Liguori <anthony@codemonkey.ws> writes:

> Rusty Russell <rusty@rustcorp.com.au> writes:
>
>> "Michael S. Tsirkin" <mst@redhat.com> writes:
>>
>> No, because I don't understand it.  Is it true for the case of
>> virtio_blk, which has outstanding requests?
>>
>>>> Currently we dump a massive structure; it's inelegant at the very
>>>> least.
>
> Inelegant is a kind word..
>
> There's a couple things to consider though which is why this code hasn't
> changed so far.
>
> 1) We're writing native endian values to the wire.  This is seriously
>    broken.  Just imagine trying to migrate from qemu-system-i386 on an
>    big endian box to a little endian box.
>
> 2) Fixing (1) either means (a) breaking migration across the board
>    gracefully or (b) breaking migration on [big|little] endian hosts in
>    an extremely ungraceful way.
>
> 3) We send a ton of crap over the wire that is unnecessary, but we need
>    to maintain it.
>
> I wrote up a patch series to try to improve the situation that I'll send
> out.  I haven't gotten around to testing it with an older version of
> QEMU yet.
>
> I went for 2.b and choose to break big endian hosts.

Since we only actually want to save the descriptor head, I was planning
on a new format version.  That will fix both...

Look forward to your patch,
Rusty.