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

[Daniel P. Berrange]

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 (address@hidden) 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
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