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: NOliver Neukum <oliver@neukum.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/usb-skeleton.c

@@ -268,6 +268,11 @@ static ssize_t skel_read(struct file *file, char *buffer, size_t count, loff_t *
 	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
@@ -351,8 +356,9 @@ static ssize_t skel_read(struct file *file, char *buffer, size_t count, loff_t *
 		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);