Re: Allocating buffers for USB transfers (again)

From: Daniel Mack
Date: Wed Aug 10 2011 - 11:33:20 EST

This is a multi-part message in MIME format.On 08/10/2011 04:32 PM, Alan Stern wrote:
Looking at the driver's current code, it appears that your patch
does not fix the bug properly. Using discontiguous regions in the
transfer buffer is perfectly okay. The real problem is later on,
where you do:

if (send_it) { out->number_of_packets = FRAMES_PER_URB;

This should be

out->number_of_packets = outframe;

The way it is now, the USB stack will try to use data from all the
frame descriptors, and the last few will be stale because the loop
doesn't set them.

That's actually true, even though it doesn't seem to cause any trouble.
I tested everything here of course, and the output URBs return back from
the USB stack with their length fields zeroed out, which then
causes the stack to send packets with zero-length fields at the end.

However, doing it right doesn't harm either. Thanks for spotting.

Takashi, can you apply this version?