Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756289AbcDGMxe (ORCPT ); Thu, 7 Apr 2016 08:53:34 -0400 Received: from mail-lf0-f47.google.com ([209.85.215.47]:35931 "EHLO mail-lf0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753821AbcDGMxa (ORCPT ); Thu, 7 Apr 2016 08:53:30 -0400 Date: Thu, 7 Apr 2016 15:53:26 +0300 From: Cyrill Gorcunov To: LKML Cc: Jiri Slaby , Peter Hurley , Greg Kroah-Hartman , Andrey Vagin , Pavel Emelianov , Vladimir Davydov , Konstantin Khorenko Subject: [PATCH resend v2] tty: n_tty -- Add new TIOCPEEKRAW ioctl to peek unread data Message-ID: <20160407125326.GH2258@uranus.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3477 Lines: 92 Currently when we checkpoint PTY connections we ignore data queued inside read buffer of ldisk, such data is barely lost after the restore. So we would like to have an ability to dump and restore it. Here is a new ioctl code which simply copies data from read buffer into the userspace without any additional processing (just like terminal is sitting in a raw mode). The idea behind is when we checkpointing PTY pairs we peek this unread data into images on disk and on restore phase we find the linked peer and write it back thus reading peer will see it in read buffer. I tried several approaches (including simply reuse of canon_copy_from_read_buf and copy_from_read_buf) but it makes code more complicated, so I end up in plain copying of buffer data. Strictly speaking, we could try handle it inside CRIU itself, as Peter Hurley proposed (switch terminal to raw mode, read data, and return original termios back) but in this case we may hit the scenario when we read data and failed to restore it back (due to any error) leaving the task we're dumping without read buffer, thus peeking data looks like be the only safe way. v2: - Use @char in ioctl definition. Signed-off-by: Cyrill Gorcunov CC: Jiri Slaby CC: Peter Hurley CC: Greg Kroah-Hartman CC: Andrey Vagin CC: Pavel Emelianov CC: Vladimir Davydov CC: Konstantin Khorenko --- drivers/tty/n_tty.c | 22 ++++++++++++++++++++++ include/uapi/asm-generic/ioctls.h | 1 + 2 files changed, 23 insertions(+) Index: linux-ml.git/drivers/tty/n_tty.c =================================================================== --- linux-ml.git.orig/drivers/tty/n_tty.c +++ linux-ml.git/drivers/tty/n_tty.c @@ -2420,6 +2420,26 @@ static unsigned long inq_canon(struct n_ return nr; } +static ssize_t n_tty_peek_raw(struct tty_struct *tty, unsigned char __user *buf) +{ + struct n_tty_data *ldata = tty->disc_data; + ssize_t retval; + + if (!mutex_trylock(&ldata->atomic_read_lock)) + return -EAGAIN; + + down_read(&tty->termios_rwsem); + retval = read_cnt(ldata); + if (retval) { + const unsigned char *from = read_buf_addr(ldata, ldata->read_tail); + if (copy_to_user(buf, from, retval)) + retval = -EFAULT; + } + up_read(&tty->termios_rwsem); + mutex_unlock(&ldata->atomic_read_lock); + return retval; +} + static int n_tty_ioctl(struct tty_struct *tty, struct file *file, unsigned int cmd, unsigned long arg) { @@ -2437,6 +2457,8 @@ static int n_tty_ioctl(struct tty_struct retval = read_cnt(ldata); up_write(&tty->termios_rwsem); return put_user(retval, (unsigned int __user *) arg); + case TIOCPEEKRAW: + return n_tty_peek_raw(tty, (unsigned char __user *) arg); default: return n_tty_ioctl_helper(tty, file, cmd, arg); } Index: linux-ml.git/include/uapi/asm-generic/ioctls.h =================================================================== --- linux-ml.git.orig/include/uapi/asm-generic/ioctls.h +++ linux-ml.git/include/uapi/asm-generic/ioctls.h @@ -77,6 +77,7 @@ #define TIOCGPKT _IOR('T', 0x38, int) /* Get packet mode state */ #define TIOCGPTLCK _IOR('T', 0x39, int) /* Get Pty lock state */ #define TIOCGEXCL _IOR('T', 0x40, int) /* Get exclusive mode state */ +#define TIOCPEEKRAW _IOR('T', 0x41, char) #define FIONCLEX 0x5450 #define FIOCLEX 0x5451