Re: [Qemu-devel] [Patch V1 2/3] xen/usb: add capability for passing through isoc jobs to host devices

[Juergen Gross <jgross@suse.com>]

On 09/09/2015 02:01 PM, Gerd Hoffmann wrote:
>    Hi,
>
>>> So, the signaling needs to be different.  The host adapter needs to
>>> signal somehow that it can handle async iso packets.  One way would be
>>> to flag this per usb bus, another one per usb packet.  Also all xen
>>> naming and the xen inlude should go away.  BTW: does this build without
>>> xen-devel installed?
>>
>> Okay, I'll try to make it more generic. I think the async iso capability
>> should be a bus attribute.
>
> Makes sense.
>
>>> Can we get rid of the callbacks?  By filling the USBPacket iovec with
>>> the iso request chunks for example?
>>
>> Difficult. One iso request chunk could require multiple iovec entries.
>
> Why multiple small iovecs instead of one big iovec?

The guest buffer might span multiple physical non contiguous pages. I
don't want to copy data to a new buffer due to performance reasons
(there is already at least one copy operation done by qemu).

> usb_host_req_complete_iso_xen() returns a single status for the whole
> USBPacket anyway ...

I need status per iso request, and libusb does deliver that.

>> The RFC version tried to avoid the callbacks and there you didn't like
>> exposing the additional structures.
>
> -ENOPATCH.

Aah, sorry, my fault. I think this was part of the off-list discussion
we had.


Juergen