[PATCH] fix sigio on tty drivers outgoing

This went into 2.4.18

drivers/char/n_tty.c

@@ -23,6 +23,11 @@
  * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of 
  *		the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
  *		who actually finally proved there really was a race.
+ *
+ * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
+ *		waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
+ *		Also fixed a bug in BLOCKING mode where write_chan returns
+ *		EAGAIN
  */
 
 #include <linux/types.h>
@@ -707,6 +712,22 @@ static int n_tty_receive_room(struct tty_struct *tty)
 	return 0;
 }
 
+/*
+ * Required for the ptys, serial driver etc. since processes
+ * that attach themselves to the master and rely on ASYNC
+ * IO must be woken up
+ */
+
+static void n_tty_write_wakeup(struct tty_struct *tty)
+{
+	if (tty->fasync)
+	{
+ 		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+		kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
+	}
+	return;
+}
+
 static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 			      char *fp, int count)
 {
@@ -1156,6 +1177,8 @@ static ssize_t write_chan(struct tty_struct * tty, struct file * file,
 			while (nr > 0) {
 				ssize_t num = opost_block(tty, b, nr);
 				if (num < 0) {
+					if (num == -EAGAIN)
+						break;
 					retval = num;
 					goto break_out;
 				}
@@ -1235,6 +1258,6 @@ struct tty_ldisc tty_ldisc_N_TTY = {
 	normal_poll,		/* poll */
 	n_tty_receive_buf,	/* receive_buf */
 	n_tty_receive_room,	/* receive_room */
-	0			/* write_wakeup */
+	n_tty_write_wakeup	/* write_wakeup */
 };