Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Feb 27, 2017 at 04:00:15PM +0100, Andrea Arcangeli wrote:
> Hello,
> 
> On Mon, Feb 27, 2017 at 11:26:58AM +0000, Dr. David Alan Gilbert wrote:
> > * Alexey Perevalov (a.perevalov@samsung.com) wrote:
> > > Also if I'm not wrong, commands and pages are transferred over the same
> > > socket. Why not to use OOB TCP in this case for commands?
> > 
> > My understanding was that OOB was limited to quite small transfers
> > I think the right way is to use a separate FD for the requests, so I'll
> > do it after Juan's multifd series.
> 
> OOB would do the trick and we considered it some time ago, but we need
> this to work over any network pipe including TLS (out of control of
> qemu but setup by libvirt), and OOB being a protocol level TCP
> specific feature in the kernel, I don't think there's any way to
> access it through TLS APIs abstractions. Plus like David said there
> are issues with the size of the transfer.

Correct, there's no facility for handling OOB data when a socket is
using TLS. Also note that QEMU might not even have a TCP socket,
as when libvirt is tunnelling migration over the libvirtd connection,
QEMU will just be given a UNIX socket or even a anoymous pipe. So any
use of OOB data is pretty much out of the question. 

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://entangle-photo.org       -o-    http://search.cpan.org/~danberr/ :|