Re: [PATCH/RFC 0/1] Vhost User Cross Cable: Intro

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Jan 10, 2020 at 10:34 AM Marc-André Lureau
<marcandre.lureau@gmail.com> wrote:
> On Wed, Jan 8, 2020 at 5:57 AM V. <mail@winaoe.org> wrote:

Hi V.,
I think I remember you from Etherboot/gPXE days :).

> > 3.
> > Now if Cross Cable is actually a new and (after a code-rewrite of 10) a viable way to connect 2 QEMU's together, could I actually
> > suggest a better way?
> > I am thinking of a '-netdev vhost-user-slave' option to connect (as client or server) to a master QEMU running '-netdev vhost-user'.
> > This way there is no need for any external program at all, the master can have it's memory unshared and everything would just work
> > and be fast.
> > Also the whole thing can fall back to normal virtio if memory is not shared and it would even work in pure usermode without any
> > context switch.
> >
> > Building a patch for this idea I could maybe get around to, don't clearly have an idea how much work this would be but I've done
> > crazier things.
> > But is this is something that someone might be able to whip up in an hour or two? Someone who actually does have a clue about vhost
> > and virtio maybe? ;-)
>
> I believe https://wiki.qemu.org/Features/VirtioVhostUser is what you
> are after. It's still being discussed and non-trivial, but not very
> active lately afaik.

virtio-vhost-user is being experimented with in the SPDK community but
there has been no activity on VIRTIO standardization or the QEMU
patches for some time.  More info here:
https://ndragazis.github.io/spdk.html

I think the new ivshmem v2 feature may provide the functionality you
are looking for, but I haven't looked at them yet.  Here is the link:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg668749.html

And here is Jan's KVM Forum presentation on ivshmem v2:
https://www.youtube.com/watch?v=TiZrngLUFMA

Stefan