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Subject[PATCH] revision: POLL_OUT for ttys, serial drivers
    Hi!

This revised version of the patch includes a fix for serial.c as well,
since it had the same problem, and a minor change in the second fix.
Please use this version instead of the previous one.

Cheers,
Sapan
--- /tmp/work/linux/drivers/char/serial.c Tue Feb 26 01:07:57 2002
+++ /usr/src/linux-2.4.18/drivers/char/serial.c Sat Apr 6 11:29:22 2002
@@ -57,6 +57,10 @@
* 10/00: add in optional software flow control for serial console.
* Kanoj Sarcar <kanoj@sgi.com> (Modified by Theodore Ts'o)
*
+ * 4/02: added TTY_DO_WRITE_WAKEUP to enable n_tty to send POLL_OUTS
+ * to waiting processes
+ * Sapan Bhatia <sapan@corewars.org>
+ *
*/

static char *serial_version = "5.05c";
@@ -3233,6 +3237,7 @@
#ifdef SERIAL_DEBUG_OPEN
printk("rs_open ttys%d successful...", info->line);
#endif
+ set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
return 0;
}

--- /tmp/work/linux/drivers/char/pty.c Fri Dec 21 23:11:54 2001
+++ /usr/src/linux-2.4.18/drivers/char/pty.c Thu Mar 21 20:26:01 2002
@@ -5,6 +5,10 @@
*
* Added support for a Unix98-style ptmx device.
* -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
+ * Added TTY_DO_WRITE_WAKEUP to enable n_tty to send POLL_OUT to
+ * waiting writers -- Sapan Bhatia <sapan@corewars.org>
+ *
+ *
*/

#include <linux/config.h>
@@ -331,6 +335,8 @@
clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
wake_up_interruptible(&pty->open_wait);
set_bit(TTY_THROTTLED, &tty->flags);
+ set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+
/* Register a slave for the master */
if (tty->driver.major == PTY_MASTER_MAJOR)
tty_register_devfs(&tty->link->driver,
--- /tmp/work/linux/drivers/char/n_tty.c Fri Apr 6 23:12:55 2001
+++ /usr/src/linux-2.4.18/drivers/char/n_tty.c Sat Mar 30 12:39:14 2002
@@ -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>
@@ -711,6 +716,22 @@
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 +1178,8 @@
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 +1259,6 @@
normal_poll, /* poll */
n_tty_receive_buf, /* receive_buf */
n_tty_receive_room, /* receive_room */
- 0 /* write_wakeup */
+ n_tty_write_wakeup /* write_wakeup */
};
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