Re: [Query] Flow of PCI device dedicated to a domU

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

On 17/07/14 07:34, Xenbegn developer wrote:
> On 7/16/14, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>> On 16/07/14 07:12, Xenbegn developer wrote:
>>> Hi,
>>> I am trying to understand the flow of how a PCI device driver in domU
>>> works after a PCI device is is assigned to a domU.
>>>
>>> a) If a PCI device is assigned to a domU, this device has to be on a
>>> PCI bus. So as per my view xen would have to somehow provide a PCI
>>> Controller on which this device is attached.
>>> => Is my assumption correct ? If yes how it is done, No then also How
>>> enumeration of this device happens in domU kernel
>> No.
>>
>> PV guests have no PCI root ports/bridges; they use devices as single
>> entities knowing that Xen/dom0 takes care of the other bits. HVM guests
>> have their PCI devices attached to the virtual southbridge which is all
>> emulated by Qemu.
>>
> How would a then a PV guest know about existence of a PCI device if it
> does not enumerate. Can you please elaborate on this.

The pcifront driver is capable of finding any PCI devices offered by
pciback in dom0.  It is all paravirtualised, and doesn't need explicit
hardware probing.

~Andrew