From: "Sapan J . Bhatia" <lists@corewars.org>
To: marcelo@conectiva.com.br, torvalds@transmeta.com, akpm@zip.com.au
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] POLL_OUT in ttys, misc bug fix
Date: Wed, 27 Mar 2002 03:24:09 +0530 [thread overview]
Message-ID: <20020327032408.A7073@corewars.org> (raw)
[-- Attachment #1: Type: text/plain, Size: 719 bytes --]
Hello,
While fixing a flow control bug that truncated output to a terminal in
User Mode Linux, I noticed that the tty drivers only send POLL_IN on new
data being available but not POLL_OUT when the device is ready for new
data.
This patch fixes the bug in the line discipline and the pty driver.
Also, there's another minor bug in n_tty.c where write_chan returns
on a (retvalue < 0) unconditionally. This is a problem, since the type of
IO (BLOCKING / NON_BLOCKING) is stored in the tty, and if the console driver
returns a -EAGAIN (eg. in UML on getting an EAGAIN from the host kernel),
write_chan returns even in the case of a blocking write, which is wrong
since the process doesn't expect it.
Regards,
Sapan
[-- Attachment #2: tty_patch.diff --]
[-- Type: text/plain, Size: 2466 bytes --]
--- /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 Thu Mar 21 07:22:44 2002
@@ -23,6 +23,13 @@
* 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>
+ *
+ * 2002/03/19 Fixed write_chan to stay put if console driver returns
+ * EAGAIN and not return since it returns an EAGAIN in a
+ * non-blocking operation-Sapan Bhatia <sapan@corewars.org>
*/
#include <linux/types.h>
@@ -711,6 +718,22 @@
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)
{
@@ -1156,7 +1179,7 @@
if (O_OPOST(tty) && !(test_bit(TTY_HW_COOK_OUT, &tty->flags))) {
while (nr > 0) {
ssize_t num = opost_block(tty, b, nr);
- if (num < 0) {
+ if (num < 0 && num != -EAGAIN) {
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 */
};
next reply other threads:[~2002-03-26 21:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-26 21:54 Sapan J . Bhatia [this message]
2002-04-04 19:56 ` [PATCH] POLL_OUT in ttys, misc bug fix Marcelo Tosatti
2002-04-06 13:51 Sapan J . Bhatia
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