hand edited Date: Wed, 27 Mar 2002 03:24:09 +0530 From: "Sapan J . Bhatia" 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 Message-ID: <20020327032408.A7073@corewars.org> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="HcAYCG3uE/tztfnV" Content-Disposition: inline User-Agent: Mutt/1.2.5i X-Operating-System: Linux corewars 2.4.18 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org --HcAYCG3uE/tztfnV Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 --HcAYCG3uE/tztfnV Content-Type: text/plain; charset=us-ascii Content-Description: tty_patch.diff Content-Disposition: attachment; filename="tty_bugs.diff" --- linux/drivers/char/pty.c Fri Dec 21 23:11:54 2001 +++ 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 , 14-Jan-1998 + * Added TTY_DO_WRITE_WAKEUP to enable n_tty to send POLL_OUT to + * waiting writers -- Sapan Bhatia + * + * */ #include @@ -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, --- linux/drivers/char/n_tty.c Fri Apr 6 23:12:55 2001 +++ 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 * 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 + * + * 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 */ #include @@ -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 */ }; --HcAYCG3uE/tztfnV-- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/