Re: [Xen-devel] error when pass through device to guest with qemu-xen-dir-remote

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On 09/18/2012 01:46 AM, Zhang, Yang Z wrote:
> Zhang, Yang Z wrote on 2012-09-11:
> >   wrote on August 09, 2012 2:49 PM To: Ian Campbell; Stefano Stabellini:
> > > I rebuild the upstream QEMU according to the wiki, but device static
> > > assignment doesn't work, no lspci output in guest. However hotplug &
> > > unplug works fine.
> > >
> > > -----Original Message----- From: xen-devel-bounces@xxxxxxxxxxxxx
> > > [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of Ian Campbell Sent:
> > > Friday, August 03, 2012 6:36 PM To: Stefano Stabellini Cc: Zhang, Yang
> > > Z; Anthony Perard; xen-devel Subject: Re: [Xen-devel] error when pass
> > > through device to guest with qemu-xen-dir-remote
> > >
> > > On Fri, 2012-08-03 at 11:29 +0100, Stefano Stabellini wrote:
> > > > On Fri, 3 Aug 2012, Zhang, Yang Z wrote:
> > > > > When create guest with device assigned, it shows the error and the
> > > > > device wasn't able to work inside guest: libxl: error:
> > > > > libxl_qmp.c:288:qmp_handle_error_response: received an error message
> > > > > from QMP server: Parameter 'driver' expects a driver name
> > > > >
> > > > > It only fails with qemu-xen-dir-remote(Is this tree more close to
> > > > > upstream qemu?). I don't see the error with the traditional Qemu. I
> > > > > also tried qemu-upstream, but it fails when I try to enable pci
> > > > > pass-through
> > > for xen. I think Anthony's patch to add pci pass-through support for Xen is
> > > accepted by qemu-upstream, am I right?
> > > > Yes, it was accepted, but it is present only in upstream QEMU (from
> > > > git://git.qemu.org/qemu.git), not the tree we are currently using in
> > > > xen-unstable for development
> > > > (git://xenbits.xensource.com/qemu-upstream-unstable.git).
> > > > Make sure you are using the right tree!
> > > http://wiki.xen.org/wiki/QEMU_Upstream has some notes on how to use the
> > > upstream qemu tree instead of our stable branch of upstream.
> > >
> > > > Anthony is currently on vacation and is going to be back in about a
> > > > week.
> > > >
> > > > > Another question:
> > > > > Now I am trying to add some features (relevant to pass through device) to
> > > Qemu, which tree should I use? Since traditional qemu is great
> > > different from qemu-upstream, it is too old to develop patch base on
> > > it. But besides the old one, I cannot find a working qemu.
> > > > You should use upstream QEMU, I am going to rebase our tree on that
> > > > early on in the 4.3 release cycle.
> > Hi Anthony
> >
> > I found the issue is caused by PV driver. Since RHEL6 integrated PV driver by
> > default, when booting rhel6 as guest, it will load the PV driver and write the 
> > xen
> > platform device to notify qemu to unplug all NICs including the pass through
> > device. This definitely is wrong. We only need to unplug the emulator device, 
> > and
> > leave pass through device.
> Hi Anthony,
>
> Any comments for this?
Hi,

So, we'll have to add a check in the unplug code of qemu to ignore 
passthrough devices.
Here is a patches, I did not test it.

diff --git a/hw/xen_platform.c b/hw/xen_platform.c
index 0d6c2ff..2d3978e 100644
--- a/hw/xen_platform.c
+++ b/hw/xen_platform.c
@@ -85,8 +85,10 @@ static void log_writeb ...

 static void unplug_nic(PCIBus *b, PCIDevice *d, void *o)
 {
+    /* We have to ignore passthrough devices */
     if (pci_get_word(d->config + PCI_CLASS_DEVICE) ==
-            PCI_CLASS_NETWORK_ETHERNET) {
+            PCI_CLASS_NETWORK_ETHERNET
+        && strcmp(d->name, "xen-pci-passthrough") != 0) {
         qdev_free(&d->qdev);
     }
 }


Thanks,

--
Anthony PERARD

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