Re: [Qemu-devel] [virtio-comment] [PATCH] *** Vhost-pci RFC v2 ***

[Stefan Hajnoczi]

On Fri, Sep 02, 2016 at 12:27:25AM +0800, Wei Wang wrote:
> On 09/01/2016 12:07 AM, Stefan Hajnoczi wrote:
> > On Tue, Aug 30, 2016 at 10:08:01AM +0000, Wang, Wei W wrote:
> > > On Monday, August 29, 2016 11:25 PM, Stefan Hajnoczi wrote:
> > > > To: Wang, Wei W <address@hidden>
> > > > Cc: address@hidden; address@hidden; virtio-
> > > > address@hidden; address@hidden; address@hidden
> > > > Subject: Re: [virtio-comment] [PATCH] *** Vhost-pci RFC v2 ***
> > > > 
> > > > On Mon, Jun 27, 2016 at 02:01:24AM +0000, Wang, Wei W wrote:
> > > > > On Sun 6/19/2016 10:14 PM, Wei Wang wrote:
> > > > > > This RFC proposes a design of vhost-pci, which is a new virtio 
> > > > > > device type.
> > > > > > The vhost-pci device is used for inter-VM communication.
> > > > > > 
> > > > > > Changes in v2:
> > > > > > 1. changed the vhost-pci driver to use a controlq to send 
> > > > > > acknowledgement
> > > > > >     messages to the vhost-pci server rather than writing to the 
> > > > > > device
> > > > > >     configuration space;
> > > > > > 
> > > > > > 2. re-organized all the data structures and the description
> > > > > > layout;
> > > > > > 
> > > > > > 3. removed the VHOST_PCI_CONTROLQ_UPDATE_DONE socket message,
> > > > which
> > > > > > is redundant;
> > > > > > 
> > > > > > 4. added a message sequence number to the msg info structure to
> > > > > > identify socket
> > > > > >     messages, and the socket message exchange does not need to be
> > > > > > blocking;
> > > > > > 
> > > > > > 5. changed to used uuid to identify each VM rather than using the
> > > > > > QEMU
> > > > process
> > > > > >     id
> > > > > > 
> > > > > One more point should be added is that the server needs to send
> > > > > periodic socket messages to check if the driver VM is still alive. I
> > > > > will add this message support in next version.  (*v2-AR1*)
> > > > Either the driver VM could go down or the device VM (server) could go
> > > > down.  In both cases there must be a way to handle the situation.
> > > > 
> > > > If the server VM goes down it should be possible for the driver VM to
> > > > resume either via hotplug of a new device or through messages
> > > > reinitializing the dead device when the server VM restarts.
> > > I got feedbacks from people that the name of device VM and driver VM are 
> > > difficult to remember. Can we use client (or frontend) VM and server (or 
> > > backend) VM in the discussion? I think that would sound more 
> > > straightforward :)
> > We discussed this in a previous email thread.
> > 
> > Device and driver are the terms used by the virtio spec.  Anyone dealing
> > with vhost-pci design must be familiar with the virtio spec.
> > 
> > I don't see how using the terminology consistently can be confusing,
> > unless these people haven't looked at the virtio spec.  In that case
> > they have no business with working on vhost-pci because virtio is a
> > prerequisite :).
> > 
> > Stefan
> I don't disagree :)
> But "frontend/backend" is also commonly used in descriptions in virtio
> related stuff, and it seems that more people like it. It's also easier to
> describe some components in the design (e.g. a backend functionality like
> vhost-pci-net). I am not sure if you guys are also OK with it.

If you want to use frontend/backend I don't mind.  It seems clear to me.

Stefan

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