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 <wei.w.wang@xxxxxxxxx> > > Cc: kvm@xxxxxxxxxxxxxxx; qemu-devel@xxxxxxxxxx; virtio- > > comment@xxxxxxxxxxxxxxxxxxxx; mst@xxxxxxxxxx; pbonzini@xxxxxxxxxx > > 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 :) So server is the device VM? Sounds even more confusing to me :) frontend/backend is kind of ok if you really prefer it, but let's add some text that explains how this translates to device/driver that rest of text uses. > > Here are the two cases: > > Case 1: When the client VM powers off, the server VM will notice that > the connection is closed (the client calls the socket close() > function, which notifies the server about the disconnection). Then the > server will need to remove the vhost-pci device for that client VM. > When the client VM boots up and connects to the server again, the > server VM re-establishes the inter-VM communication channel (i.e. > creating a new vhost-pci device and hot-plugging it to the server VM). So on reset you really must wait for backend to stop doing things before you proceed. Closing socket won't do this, it's asynchronous. > Case 2: When the server VM powers off, the client doesn't need to do > anything. We can provide a way in QEMU monitor to re-establish the > connection. So, when the server boots up again, the admin can let a > client connect to the server via the client side QEMU monitor. > > Best, > Wei > > You need server to be careful though. If it leaves the rings in an inconsistent state, there's a problem. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
