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



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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