USB: Add URB_FREE_BUFFER flag and the logic behind it

USB: Add URB_FREE_BUFFER flag for freeing the transfer buffer

In some cases it is not needed that the driver keeps track of the
transfer buffer of an URB. It can be simply freed along with the
URB itself when the reference count goes down to zero. The new
flag URB_FREE_BUFFER enables this behavior.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/urb.c

@@ -13,6 +13,9 @@ static void urb_destroy(struct kref *kref)
 {
 	struct urb *urb = to_urb(kref);
 
+	if (urb->transfer_flags & URB_FREE_BUFFER)
+		kfree(urb->transfer_buffer);
+
 	kfree(urb);
 }
 

include/linux/usb.h

@@ -994,6 +994,7 @@ extern int usb_disabled(void);
 #define URB_ZERO_PACKET		0x0040	/* Finish bulk OUT with short packet */
 #define URB_NO_INTERRUPT	0x0080	/* HINT: no non-error interrupt
 					 * needed */
+#define URB_FREE_BUFFER		0x0100	/* Free transfer buffer with the URB */
 
 struct usb_iso_packet_descriptor {
 	unsigned int offset;