Re: [PATCH v1 3/3] migration: multifd: Enable zerocopy

[Peter Xu]

On Wed, Sep 01, 2021 at 04:44:30PM +0100, Daniel P. Berrangé wrote:
> QEMU has mptcp support already:
> 
>   commit 8bd1078aebcec5eac196a83ef1a7e74be0ba67b7
>   Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
>   Date:   Wed Apr 21 12:28:34 2021 +0100
> 
>     sockets: Support multipath TCP
>     
>     Multipath TCP allows combining multiple interfaces/routes into a single
>     socket, with very little work for the user/admin.
>     
>     It's enabled by 'mptcp' on most socket addresses:
>     
>        ./qemu-system-x86_64 -nographic -incoming tcp:0:4444,mptcp

Oops, I totally forgot about that, sorry!

> 
> > KTLS may be implicitly included by a new gnutls, but we need to mark TLS and
> > ZEROCOPY mutual exclusive anyway because at least the userspace TLS code of
> > gnutls won't has a way to maintain the tls buffers used by zerocopy.  So at
> > least we need some knob to detect whether kTLS is enabled in gnutls.
> 
> It isn't possible for gnutls to transparently enable KTLS, because
> GNUTLS doesn't get to see the actual socket directly - it'll need
> some work in QEMU to enable it.  We know MPTCP and KTLS are currently
> mutually exclusive as they both use the same kernel network hooks
> framework.

Then we may need to at least figure out whether zerocopy needs to mask out
mptcp.

-- 
Peter Xu