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

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

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On 22/07/14 10:43, Xenbegn developer wrote:
>
>
>
> On Thu, Jul 17, 2014 at 3:12 PM, Andrew Cooper
> <andrew.cooper3@citrix.com <mailto:andrew.cooper3@citrix.com>> wrote:
>
>     On 17/07/14 07:34, Xenbegn developer wrote:
>     > On 7/16/14, Andrew Cooper <andrew.cooper3@citrix.com
>     <mailto: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.
>
> So does this flow happens internally in xen for x86
> a) dom0 scans all the pci devices
> b) Using libxl hypercalls a pci device is assigned to a domainU
> c) When  domU boots the pci front driver would talk to pci back driver
> and discover the PCI devices

>From a basic point of view, yes.

~Andrew

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