![Jiri Slaby](/assets/img/avatar_default.png)
When the tty_printk driver fails to create a node in sysfs, the system
crashes. It is because the driver registers a tty driver and frees it
without deregistering it first. The fix is easy: add a call to
tty_unregister_driver to the fail path.
This is very unlikely to happen in usual environment => no need for
stable.
The crash occurs at some place where we iterate over tty drivers
first. It may look like this:
BUG: unable to handle kernel paging request at ffffffffffffff84
IP: [<ffffffff81278d56>] tty_open+0xd6/0x650
PGD 1a0d067
PUD 1a0e067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
Modules linked in:
CPU 0
Pid: 1183, comm: boot.localnet Tainted: G W 3.5.0-rc7-next-20120716+ #369 Bochs Bochs
RIP: 0010:[<ffffffff81278d56>] [<ffffffff81278d56>] tty_open+0xd6/0x650
RSP: 0018:ffff8800162b3b98 EFLAGS: 00010207
RAX: 0000000000000000 RBX: ffff880016ba6200 RCX: 0000000000002208
RDX: 0000000000000000 RSI: 00000000000000d0 RDI: ffffffff81a35080
RBP: ffff8800162b3c08 R08: ffffffff81276f42 R09: 0000000000400040
R10: ffff8800161dc005 R11: ffff8800188ee048 R12: 0000000000000000
R13: ffffffffffffff58 R14: 0000000000400040 R15: 0000000000008000
FS: 00007f3684abd700(0000) GS:ffff880018e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffff84 CR3: 000000001503e000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process boot.localnet (pid: 1183, threadinfo ffff8800162b2000, task ffff8800188c5880)
Stack:
ffff8800162b3c08 ffffffff81363d63 ffffffff81a62940 ffff8800189b4e88
ffff8800188c5880 ffffffff81123180 0000000000000000 ffffffff18b20600
0000000000000000 ffff8800189b4e88 ffff880016ba6200 ffff880018b20600
Call Trace:
[<ffffffff81363d63>] ? kobj_lookup+0x103/0x160
[<ffffffff81123180>] ? mount_fs+0x110/0x110
[<ffffffff81123a9c>] chrdev_open+0x9c/0x1a0
[<ffffffff81123a00>] ? cdev_put+0x30/0x30
[<ffffffff8111de76>] do_dentry_open.isra.19+0x1e6/0x270
[<ffffffff8111df65>] finish_open+0x65/0xa0
[<ffffffff8112dc9e>] do_last.isra.52+0x26e/0xd80
[<ffffffff8112b163>] ? inode_permission+0x13/0x50
[<ffffffff8112b203>] ? link_path_walk+0x63/0x940
[<ffffffff8112e85b>] path_openat+0xab/0x3d0
[<ffffffff8112ef5d>] do_filp_open+0x3d/0xa0
[<ffffffff8113ba72>] ? alloc_fd+0xd2/0x120
[<ffffffff8111eee3>] do_sys_open+0xf3/0x1d0
[<ffffffff8111efdc>] sys_open+0x1c/0x20
[<ffffffff815b5fe2>] system_call_fastpath+0x16/0x1b
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Samo Pogacnik <samo_pogacnik@t-2.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
226 lines
5.2 KiB
C
226 lines
5.2 KiB
C
/*
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* linux/drivers/char/ttyprintk.c
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*
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* Copyright (C) 2010 Samo Pogacnik
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the smems of the GNU General Public License as published by
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* the Free Software Foundation; version 2 of the License.
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*/
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/*
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* This pseudo device allows user to make printk messages. It is possible
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* to store "console" messages inline with kernel messages for better analyses
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* of the boot process, for example.
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*/
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#include <linux/device.h>
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#include <linux/serial.h>
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#include <linux/tty.h>
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#include <linux/export.h>
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struct ttyprintk_port {
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struct tty_port port;
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struct mutex port_write_mutex;
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};
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static struct ttyprintk_port tpk_port;
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/*
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* Our simple preformatting supports transparent output of (time-stamped)
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* printk messages (also suitable for logging service):
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* - any cr is replaced by nl
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* - adds a ttyprintk source tag in front of each line
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* - too long message is fragmeted, with '\'nl between fragments
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* - TPK_STR_SIZE isn't really the write_room limiting factor, bcause
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* it is emptied on the fly during preformatting.
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*/
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#define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
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#define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
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static const char *tpk_tag = "[U] "; /* U for User */
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static int tpk_curr;
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static int tpk_printk(const unsigned char *buf, int count)
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{
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static char tmp[TPK_STR_SIZE + 4];
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int i = tpk_curr;
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if (buf == NULL) {
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/* flush tmp[] */
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if (tpk_curr > 0) {
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/* non nl or cr terminated message - add nl */
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tmp[tpk_curr + 0] = '\n';
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tmp[tpk_curr + 1] = '\0';
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printk(KERN_INFO "%s%s", tpk_tag, tmp);
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tpk_curr = 0;
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}
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return i;
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}
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for (i = 0; i < count; i++) {
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tmp[tpk_curr] = buf[i];
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if (tpk_curr < TPK_STR_SIZE) {
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switch (buf[i]) {
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case '\r':
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/* replace cr with nl */
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tmp[tpk_curr + 0] = '\n';
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tmp[tpk_curr + 1] = '\0';
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printk(KERN_INFO "%s%s", tpk_tag, tmp);
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tpk_curr = 0;
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if (buf[i + 1] == '\n')
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i++;
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break;
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case '\n':
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tmp[tpk_curr + 1] = '\0';
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printk(KERN_INFO "%s%s", tpk_tag, tmp);
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tpk_curr = 0;
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break;
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default:
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tpk_curr++;
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}
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} else {
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/* end of tmp buffer reached: cut the message in two */
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tmp[tpk_curr + 1] = '\\';
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tmp[tpk_curr + 2] = '\n';
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tmp[tpk_curr + 3] = '\0';
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printk(KERN_INFO "%s%s", tpk_tag, tmp);
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tpk_curr = 0;
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}
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}
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return count;
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}
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/*
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* TTY operations open function.
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*/
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static int tpk_open(struct tty_struct *tty, struct file *filp)
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{
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tty->driver_data = &tpk_port;
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return tty_port_open(&tpk_port.port, tty, filp);
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}
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/*
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* TTY operations close function.
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*/
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static void tpk_close(struct tty_struct *tty, struct file *filp)
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{
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struct ttyprintk_port *tpkp = tty->driver_data;
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mutex_lock(&tpkp->port_write_mutex);
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/* flush tpk_printk buffer */
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tpk_printk(NULL, 0);
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mutex_unlock(&tpkp->port_write_mutex);
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tty_port_close(&tpkp->port, tty, filp);
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}
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/*
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* TTY operations write function.
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*/
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static int tpk_write(struct tty_struct *tty,
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const unsigned char *buf, int count)
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{
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struct ttyprintk_port *tpkp = tty->driver_data;
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int ret;
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/* exclusive use of tpk_printk within this tty */
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mutex_lock(&tpkp->port_write_mutex);
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ret = tpk_printk(buf, count);
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mutex_unlock(&tpkp->port_write_mutex);
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return ret;
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}
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/*
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* TTY operations write_room function.
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*/
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static int tpk_write_room(struct tty_struct *tty)
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{
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return TPK_MAX_ROOM;
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}
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/*
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* TTY operations ioctl function.
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*/
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static int tpk_ioctl(struct tty_struct *tty,
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unsigned int cmd, unsigned long arg)
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{
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struct ttyprintk_port *tpkp = tty->driver_data;
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if (!tpkp)
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return -EINVAL;
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switch (cmd) {
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/* Stop TIOCCONS */
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case TIOCCONS:
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return -EOPNOTSUPP;
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default:
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return -ENOIOCTLCMD;
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}
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return 0;
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}
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static const struct tty_operations ttyprintk_ops = {
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.open = tpk_open,
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.close = tpk_close,
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.write = tpk_write,
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.write_room = tpk_write_room,
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.ioctl = tpk_ioctl,
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};
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static struct tty_port_operations null_ops = { };
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static struct tty_driver *ttyprintk_driver;
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static int __init ttyprintk_init(void)
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{
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int ret = -ENOMEM;
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void *rp;
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ttyprintk_driver = alloc_tty_driver(1);
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if (!ttyprintk_driver)
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return ret;
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ttyprintk_driver->driver_name = "ttyprintk";
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ttyprintk_driver->name = "ttyprintk";
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ttyprintk_driver->major = TTYAUX_MAJOR;
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ttyprintk_driver->minor_start = 3;
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ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
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ttyprintk_driver->init_termios = tty_std_termios;
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ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
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ttyprintk_driver->flags = TTY_DRIVER_RESET_TERMIOS |
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TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
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tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
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ret = tty_register_driver(ttyprintk_driver);
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if (ret < 0) {
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printk(KERN_ERR "Couldn't register ttyprintk driver\n");
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goto error;
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}
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/* create our unnumbered device */
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rp = device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 3), NULL,
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ttyprintk_driver->name);
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if (IS_ERR(rp)) {
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printk(KERN_ERR "Couldn't create ttyprintk device\n");
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ret = PTR_ERR(rp);
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goto error;
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}
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tty_port_init(&tpk_port.port);
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tpk_port.port.ops = &null_ops;
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mutex_init(&tpk_port.port_write_mutex);
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return 0;
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error:
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tty_unregister_driver(ttyprintk_driver);
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put_tty_driver(ttyprintk_driver);
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ttyprintk_driver = NULL;
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return ret;
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}
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module_init(ttyprintk_init);
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