From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ross Lagerwall <ross.lagerwall@citrix.com>
Subject: Re: [PATCH] libxl: Don't insert PCI device into
 xenstore for HVM guests
Date: Fri, 29 May 2015 10:54:09 +0100
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To: Wei Liu <wei.liu2@citrix.com>
Cc: xen-devel@lists.xen.org, Ian Jackson <ian.jackson@eu.citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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On 05/29/2015 10:50 AM, Wei Liu wrote:
> On Fri, May 29, 2015 at 10:43:08AM +0100, Ross Lagerwall wrote:
>> On 05/29/2015 10:41 AM, Wei Liu wrote:
>>> On Fri, May 29, 2015 at 08:59:45AM +0100, Ross Lagerwall wrote:
>>>> When doing passthrough of a PCI device for an HVM guest, don't insert
>>>> the device into xenstore, otherwise pciback attempts to use it which
>>>> conflicts with QEMU.
>>>>
>>>> This manifests itself such that the first time a device is passed to a
>>>> domain, it succeeds. Subsequent attempts fail unless the device is
>>>> unbound from pciback or the machine rebooted.
>>>>
>>>
>>> The commit message looks sensible to me. However this might break
>>> qemu-trad PCI passthrough if I'm not mistaken. What QEMU version are you
>>> using?  Upstream or trad? Have you tested both of them?
>>>
>>
>> qemu-trad. I haven't tested with qemu-upstream.
>>
>
> I don't quite get this. Doesn't qemu-trad depends on those xenstore
> nodes for PCI passthrough information?  What did I miss?
>

A different set of xenstore keys are used for communication between 
libxl and QEMU. The communication between libxl and QEMU happens further 
up in the same function:
http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/libxl/libxl_pci.c;h=e0743f8112689b340ba7de88bc8895b62105aaba;hb=HEAD#l901

Regards,
-- 
Ross Lagerwall