Re: [Qemu-devel] [PATCH] Peek dont read for vmdescription

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Alexander Graf (agraf@suse.de) wrote:
> 
> 
> On 22.06.15 16:49, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > The VMDescription section maybe after the EOF mark, the current code
> > does a 'qemu_get_byte' and either gets the header byte identifying the
> > description or an error (which it ignores).  Doing the 'get' upsets
> > RDMA which hangs on old machine types without the VMDescription.
> > 
> > Using 'qemu_peek_byte' avoids that.
> > 
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> Fun. I did actually use peek at first and then figured it's the same as
> read in the qemu file implementation. Have you figured out why exactly
> peek does make a difference for the RDMA case?

Yeh, scrap this patch.

I've just posted 

'Only try and read a VMDescription if it should be there'

as a replacement.
Fundamentally, the trick of trying to send/read stuff after the EOF
just isn't safe on all transports.  We've got to read stuff if it's
expected and only if it's expected and obey the EOF marker.  If it
wasn't for keeping compatibility I'd swing this section around so it
went before the EOF, but we can't break compatibility with streams
that already have it.

Dave

> 
> 
> Alex
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK