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

From: Stefan Hajnoczi
Subject: Re: [PATCH/RFC 0/1] Vhost User Cross Cable: Intro
Date: Tue, 14 Jan 2020 10:20:09 +0000

On Fri, Jan 10, 2020 at 10:34 AM Marc-André Lureau
<address@hidden> wrote:
> On Wed, Jan 8, 2020 at 5:57 AM V. <address@hidden> 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:

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:

And here is Jan's KVM Forum presentation on ivshmem v2:


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