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Re: [Qemu-devel] RFC: Universal encryption on QEMU I/O channels

From: Daniel P. Berrange
Subject: Re: [Qemu-devel] RFC: Universal encryption on QEMU I/O channels
Date: Wed, 4 Feb 2015 15:11:06 +0000
User-agent: Mutt/1.5.23 (2014-03-12)

On Wed, Feb 04, 2015 at 04:04:33PM +0100, Paolo Bonzini wrote:
> On 04/02/2015 15:34, Daniel P. Berrange wrote:
> > > GIO doesn't provide writev either, so it's not a good match for
> > > non-encrypted migration, which really tries hard to do no copies in
> > > userspace.
> > 
> > Ok, maybe RDMA will still need QEMUFile, but for non-encrypted TCP
> > I'd hope to be able to achieve zero-copy with the new API too - it
> > would certainly be my intention/goal.
> For GIO/GIOChannel, you'd have to choose between zerocopy and many
> syscalls, or one copy and few syscalls.  Since every page has two iov
> entries, one of which is just 8 bytes, one copy and few syscalls is
> probably faster---but still only half the speed of writev.

That could be an argument in favour of defining a QEMUIOChannel
instead. The use of GIOChannel is only compelling if we gain some
significant benefit from using the standard glib API in this scenario
and I'm not clear that we really do, other than developer familiarity
with glib. GIO could be compelling if we could leverage its TLS

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