RE: [PATCH] [2.5] Non-blocking write can block

[Hua Zhong <hzhong@cisco.com>]

> Do y ou have that other patch handy? It sounds like that is 
> the real cause of the problem, and the patch quoted originally 
> in this thread was a (broken) work-around..
> 
>                Linus
> 

Something like this:

--- n_tty.c.old	2003-06-04 12:28:36.000000000 -0700
+++ n_tty.c	2003-06-04 12:28:51.000000000 -0700
@@ -711,6 +711,23 @@
 	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)
 {
@@ -1157,6 +1174,8 @@
 			while (nr > 0) {
 				ssize_t num = opost_block(tty, b, nr);
 				if (num < 0) {
+					if (num == -EAGAIN)
+						break;
 					retval = num;
 					goto break_out;
 				}
@@ -1236,6 +1255,6 @@
 	normal_poll,		/* poll */
 	n_tty_receive_buf,	/* receive_buf */
 	n_tty_receive_room,	/* receive_room */
-	0			/* write_wakeup */
+ 	n_tty_write_wakeup 	/* write_wakeup */
 };