Comment 2 for bug 544527

This bugfix is incomplete. Isochronous transfers are still broken, when running 32-bit software on a 64-bit kernel. Function processcompl_compat() in devio.c needs a similar fix to the fix that was applied to processcompl(). Looking at processcompl_compat() I see:

 if (as->userbuffer && urb->actual_length)
  if (copy_to_user(as->userbuffer, urb->transfer_buffer,
     urb->actual_length))
   return -EFAULT;

correct code would be something like

 if (as->userbuffer && urb->actual_length) {
  if (urb->number_of_packets > 0) /* Isochronous */
   i = urb->transfer_buffer_length;
  else /* Non-Isoc */
   i = urb->actual_length;
  if (copy_to_user(as->userbuffer, urb->transfer_buffer, i))
   goto err_out;
 }

(note the difference between urb->actual_length and urb->transfer_buffer_length).

With kernel 2.6.32-23-generic x86_64 on Ubuntu 10.04, using proprietary USB-hardware hooked up to the USB bus (with software compiled for 32-bit), I can directly observe how isochronous transfers retrieved via ioctl(.. USBDEVFS_REAPURB ..) are too short, i.e. the kernel does not write the end of the data packet to the supplied buffer. Booting on the 2.6.31 kernel still present from before I upgraded from Ubuntu 9.10, the same software runs flawlessly.

As a workaround I'll use the older kernel for now (also I could compile for 64-bit, actually...).

cheers,

David