Re: [Qemu-devel] [virtio-dev] Re: [virtio-dev] [PATCH v3 0/7] Vhost-pci for inter-VM communication

[Stefan Hajnoczi]

On Fri, Dec 15, 2017 at 06:33:45PM +0800, Wei Wang wrote:
> On 12/15/2017 02:04 AM, Stefan Hajnoczi wrote:
> > On Thu, Dec 14, 2017 at 01:53:16PM +0800, Wei Wang wrote:
> > > 3rd one: I'm not able to solve this one, as discussed, there are too many
> > > differences and it's too complex. I prefer the direction of simply gating
> > > the vhost-user protocol and deliver to the guest what it should see (just
> > > what this patch series shows). You would need to solve this issue to show
> > > this direction is simpler :)
> > At the moment the main issue deciding what to do seems to be that we
> > have no patches for the approach I've described.  I'll begin working on
> > a patch series.
> 
> 
> Are you planning to implement the multiple masters and slaves?
> Master-->QemuSlave1-->GuestSlave
> Master<--QemuSlave2<--GuestSlave

Not sure if we are thinking of the same model.  Here's what I have in
mind:

  Master <-> QEMU virtio-vhost-user-slave <-> GuestSlave

The virtio-vhost-user-slave device implements a vhost-user slave on the
host side and a virtio device that acts as a vhost-user master to the
guest.  This is a single virtio device that speaks the vhost-user
protocol, not a family of different devices.

("virtio-vhost-user-slave" is the name to prevent confusion with your
vhost-pci work.)

I think your idea of using virtio is good since it avoids duplicating
low-level PCI device initialization and queues, so I've decided to try
that.

I will send a draft device specification later today so you can review
it.  I think the virtio PCI transport mapping that I'm documenting will
be useful whether we choose vhost-pci or virtio-vhost-user-slave.

Stefan

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