usbfs: Add support for bulk stream ids

This patch makes it possible to specify a bulk stream id when submitting
an urb using the async usbfs API. It overloads the number_of_packets
usbdevfs_urb field for this. This is not pretty, but given other
constraints it is the best we can do. The reasoning leading to this goes
as follows:

1) We want to support bulk streams in the usbfs API
2) We do not want to extend the usbdevfs_urb struct with a new member, as
   that would mean defining new ioctl numbers for all async API ioctls +
   adding compat versions for the old ones (times 2 for 32 bit support)
3) 1 + 2 means we need to re-use an existing field
4) number_of_packets is only used for isoc urbs, and streams are bulk only
   so it is the best (and only) candidate for re-using

Note that:
1) This patch only uses number_of_packets as stream_id if the app has
   actually allocated streams on the ep, so that old apps which may have
   garbage in there (as it was unused until now in the bulk case), will not
   break
2) This patch does not add support for allocating / freeing bulk-streams, that
   is done in a follow up patch

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/uapi/linux/usbdevice_fs.h b/include/uapi/linux/usbdevice_fs.h
index 0c65e4b12617..cbf122db56bc 100644
--- a/include/uapi/linux/usbdevice_fs.h
+++ b/include/uapi/linux/usbdevice_fs.h
@@ -102,7 +102,10 @@ struct usbdevfs_urb {
 	int buffer_length;
 	int actual_length;
 	int start_frame;
-	int number_of_packets;
+	union {
+		int number_of_packets;	/* Only used for isoc urbs */
+		unsigned int stream_id;	/* Only used with bulk streams */
+	};
 	int error_count;
 	unsigned int signr;	/* signal to be sent on completion,
 				  or 0 if none should be sent. */