Re: Xen 4.2 and PCI hotplug.

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 19/12/2012 09:14, Zhang, Xiantao wrote:
>> -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@suse.com]
>> Sent: Wednesday, December 19, 2012 4:48 PM
>> To: Zhang, Xiantao
>> Cc: Konrad Rzeszutek Wilk; xen-devel
>> Subject: Re: [Xen-devel] Xen 4.2 and PCI hotplug.
>>
>>>>> On 19.12.12 at 09:13, "Zhang, Xiantao" <xiantao.zhang@intel.com>
>> wrote:
>>> Are you playing with Xen ?  so far,  Xen doesn't support PCIe device
>>> hot-plug feature yet.
>> When saying Xen, I assume you mean the pv-ops kernel instead? So far I was
>> under the impression that this worked even with the very old 2.6.18 tree (as
>> much or as little as hotplug there worked in the native case). And given that
>> there are no special requirements on the hypervisor to make this work, it's
>> not even obvious to me what would be missing in the pv-ops kernel to make
>> it work. 
> Oh, my fault!  Perhaps we don't need to do anything for pv-ops kernel to support device hot-plug if native system has it supported.  Actually, we didn't do such testings before, since it is a native feature, not a Xen-specific one. 
> Xiantao

My current understanding is that on boot, Xen scans the PCI bus, then
dom0 rescans it later.  If a hotplug event gets serviced by dom0, does
there not need to be some hypercall informing Xen that a new device has
appeared?  I expect PCIPassthrough would not work correctly on a
hotplugged device which Xen is unaware of.

(But if I have got the wrong end of the stick, or this mechanism already
exist, please ignore me.  It just strikes me as a little xen-specific,
even if the bulk of it is native)

~Andrew

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