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Re: [Qemu-devel] [Patch V1 2/3] xen/usb: add capability for passing thro

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] [Patch V1 2/3] xen/usb: add capability for passing through isoc jobs to host devices
Date: Wed, 09 Sep 2015 16:43:18 +0200

> > Why multiple small iovecs instead of one big iovec?
> The guest buffer might span multiple physical non contiguous pages.

Sure, thats why we have iovecs in the first place.

>  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).

We can walk the iovec and fill the libusb struct with the pointers and
lengths instead of using usb_copy_packet ...

> > 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.

So one usbpacket per iso request should make this work.  And of you
enable pipelining for the endpoint qemu allows multiple outstanding
async packages, so you can queue up a batch of requests ...


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