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

[Alexander Graf <agraf@suse.de>]

On 23.06.15 18:37, Dr. David Alan Gilbert wrote:
> * 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.

Meh, that's truly a shame. The post-things-after-EOF-hack sounded so
great...


Alex