n_hdlc: honor O_NONBLOCK on write

Make n_hdlc line discipline honor the O_NONBLOCK file flag on write.

Signed-off-by: Paul Fulghum <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Alan Cox <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/n_hdlc.c

···
 	/* Allocate transmit buffer */
 	/* sleep until transmit buffer available */		
 	while (!(tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list))) {
+		if (file->f_flags & O_NONBLOCK) {
+			error = -EAGAIN;
+			break;
+		}
 		schedule();
 			
 		n_hdlc = tty2n_hdlc (tty);