RE: [Xen-devel] [VTD][PATCH] Change xc_assign_device()

["Han, Weidong" <weidong.han@xxxxxxxxx>]

I agree the early do those checks the better. But without mapping memory
and I/O port in qemu, the assigned device can't be really used. That's
to say the assignment is not completed in a way. In addition, if we want
to support hotplug devices, it's not suitable to do assignment in Xend.

Randy (Weidong)

Keir Fraser wrote:
> Sounds to me like qemu-dm is too late to do those other checks or you
> need better error handling in qemu-dm. Really you have a choice: do
> all tests and assignment in qemu-dm, or do all tests and assignment
> in xend. Doing half-and-half is stupid. If the pass-through can still
> fail even after the check you leave in xend, why check at all in xend?
> 
> Probably you need to fail the domain create, or at least shutdown the
> domain, when a device that should be passed through cannot be passed
> through. That will naturally cause the device assignment to be torn
> down (if it was set set up), as the domain is destroyed. Whether this
> is all actioned from xend or from qemu-dm doesn't much matter, but
> the split responsibility isn't clean. Probably xend is better just
> because the error handling is easier and earlier there.
> 
>  -- Keir
> 
> On 10/12/07 08:13, "Han, Weidong" <weidong.han@xxxxxxxxx> wrote:
> 
>> Xend is too early to do real assignment, do some checking is better.
>> These two issues will be found by the checks in Xend ( 1) issue will
>> be found by pciback). After passing these checks in Xend, it's
>> suitable to do real device assignment and memory and ioport mappings
>> in qemu. 
>> 
>> Randy (Weidong)
>> 
>> Muli Ben-Yehuda wrote:
>>> On Mon, Dec 10, 2007 at 02:21:55PM +0800, Han, Weidong wrote:
>>> 
>>>> Currently we assign devices with VT-d in Xend, this raises two
>>>> issues: 1) assign devices regardless of they are hidden by pciback
>>>> or not. If the device is not hidden, it results in the device
>>>> doesn't work in Dom0; 2) device is assigned one by one, if assign
>>>> multiple devices, some devices may have been assigned when problem
>>>> happens, it results in assigned devices don't work in Dom0. I think
>>>> Xend is not a good place to assign devices. This patch adds a
>>>> parameter to xc_assign_device(), let it just do check in Xend
>>>> whether the devices can be assigned or not, and move real device
>>>> assignment to qemu.
>>> 
>>> Why is qemu a better place to assign the devices? How does moving it
>>> to qemu solve the two issues mentioned above?
>>> 
>>> Cheers,
>>> Muli
>> 
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