[libusb] #142: Spurious short packet errors received because SHORT_NOT_OK flag is always turned on.

#142: Spurious short packet errors received because SHORT_NOT_OK flag is always
turned on.
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 Reporter:  cwn     |       Owner:
     Type:  defect  |      Status:  new
Milestone:          |   Component:  libusb-1.0 Linux backend
 Keywords:          |  Blocked By:
   Blocks:          |
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 This bug was seen in libusb 1.0.9 running on Linux kernel 3.2.0. If the
 async bulk transfer is broken up into multiple URBs, then all but the last
 URB should have the SHORT_NO_OK flag turned on so that short USB packets
 in the middle of the transfer will be reported as an error. The bug is
 that the SHORT_NOT_OK flag is always turned on even if there is only one
 URBs in the transfer. This causes any URBs that ends in a short packet to
 return any -EREMOTEIO error. The result is that when a large number of
 9206 byte async bulk transfers are queued a 300 to 400 microsecond delay
 can be seen on a USB protocol analyser between transfers.

 Changing the if statement in libusb-1.0.9/libusb/os/linux_usbfs.c on line
 1629 to check if the URB is the last URB in the transfer before turning on
 the SHORT_NOT_OK flag seems to have fixed the problem for me.

 Original Code:
                 if (supports_flag_bulk_continuation && !is_out)
                         urb->flags = USBFS_URB_SHORT_NOT_OK;

 Modified Code:
                 if (supports_flag_bulk_continuation && !is_out && i+1 !=
 num_urbs)