USB: O_NONBLOCK in read path of skeleton

Non blocking IO is supported in the read path of usb-skeleton.
This is done by just not blocking. As support for handling signals
without stopping IO is already there, it can be used for O_NONBLOCK, too.

Signed-off-by: Oliver Neukum <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/usb-skeleton.c

···
 	spin_unlock_irq(&dev->err_lock);
 
 	if (ongoing_io) {
+		/* nonblocking IO shall not wait */
+		if (file->f_flags & O_NONBLOCK) {
+			rv = -EAGAIN;
+			goto exit;
+		}
 		/*
 		 * IO may take forever
 		 * hence wait in an interruptible state
···
 		rv = skel_do_read_io(dev, count);
 		if (rv < 0)
 			goto exit;
-		else
+		else if (!file->f_flags & O_NONBLOCK)
 			goto retry;
+		rv = -EAGAIN;
 	}
 exit:
 	mutex_unlock(&dev->io_mutex);