1 // SPDX-License-Identifier: GPL-2.0-only
3 * linux/drivers/char/ttyprintk.c
5 * Copyright (C) 2010 Samo Pogacnik
9 * This pseudo device allows user to make printk messages. It is possible
10 * to store "console" messages inline with kernel messages for better analyses
11 * of the boot process, for example.
14 #include <linux/device.h>
15 #include <linux/serial.h>
16 #include <linux/tty.h>
17 #include <linux/module.h>
18 #include <linux/spinlock.h>
20 struct ttyprintk_port {
25 static struct ttyprintk_port tpk_port;
28 * Our simple preformatting supports transparent output of (time-stamped)
29 * printk messages (also suitable for logging service):
30 * - any cr is replaced by nl
31 * - adds a ttyprintk source tag in front of each line
32 * - too long message is fragmented, with '\'nl between fragments
33 * - TPK_STR_SIZE isn't really the write_room limiting factor, because
34 * it is emptied on the fly during preformatting.
36 #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
37 #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
38 #define TPK_PREFIX KERN_SOH __stringify(CONFIG_TTY_PRINTK_LEVEL)
42 static char tpk_buffer[TPK_STR_SIZE + 4];
44 static void tpk_flush(void)
47 tpk_buffer[tpk_curr] = '\0';
48 printk(TPK_PREFIX "[U] %s\n", tpk_buffer);
53 static int tpk_printk(const unsigned char *buf, int count)
62 for (i = 0; i < count; i++) {
63 if (tpk_curr >= TPK_STR_SIZE) {
64 /* end of tmp buffer reached: cut the message in two */
65 tpk_buffer[tpk_curr++] = '\\';
72 if ((i + 1) < count && buf[i + 1] == '\n')
79 tpk_buffer[tpk_curr++] = buf[i];
88 * TTY operations open function.
90 static int tpk_open(struct tty_struct *tty, struct file *filp)
92 tty->driver_data = &tpk_port;
94 return tty_port_open(&tpk_port.port, tty, filp);
98 * TTY operations close function.
100 static void tpk_close(struct tty_struct *tty, struct file *filp)
102 struct ttyprintk_port *tpkp = tty->driver_data;
105 spin_lock_irqsave(&tpkp->spinlock, flags);
106 /* flush tpk_printk buffer */
108 spin_unlock_irqrestore(&tpkp->spinlock, flags);
110 tty_port_close(&tpkp->port, tty, filp);
114 * TTY operations write function.
116 static int tpk_write(struct tty_struct *tty,
117 const unsigned char *buf, int count)
119 struct ttyprintk_port *tpkp = tty->driver_data;
124 /* exclusive use of tpk_printk within this tty */
125 spin_lock_irqsave(&tpkp->spinlock, flags);
126 ret = tpk_printk(buf, count);
127 spin_unlock_irqrestore(&tpkp->spinlock, flags);
133 * TTY operations write_room function.
135 static int tpk_write_room(struct tty_struct *tty)
141 * TTY operations ioctl function.
143 static int tpk_ioctl(struct tty_struct *tty,
144 unsigned int cmd, unsigned long arg)
146 struct ttyprintk_port *tpkp = tty->driver_data;
162 * TTY operations hangup function.
164 static void tpk_hangup(struct tty_struct *tty)
166 struct ttyprintk_port *tpkp = tty->driver_data;
168 tty_port_hangup(&tpkp->port);
171 static const struct tty_operations ttyprintk_ops = {
175 .write_room = tpk_write_room,
177 .hangup = tpk_hangup,
180 static const struct tty_port_operations null_ops = { };
182 static struct tty_driver *ttyprintk_driver;
184 static int __init ttyprintk_init(void)
188 spin_lock_init(&tpk_port.spinlock);
190 ttyprintk_driver = tty_alloc_driver(1,
191 TTY_DRIVER_RESET_TERMIOS |
192 TTY_DRIVER_REAL_RAW |
193 TTY_DRIVER_UNNUMBERED_NODE);
194 if (IS_ERR(ttyprintk_driver))
195 return PTR_ERR(ttyprintk_driver);
197 tty_port_init(&tpk_port.port);
198 tpk_port.port.ops = &null_ops;
200 ttyprintk_driver->driver_name = "ttyprintk";
201 ttyprintk_driver->name = "ttyprintk";
202 ttyprintk_driver->major = TTYAUX_MAJOR;
203 ttyprintk_driver->minor_start = 3;
204 ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
205 ttyprintk_driver->init_termios = tty_std_termios;
206 ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
207 tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
208 tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);
210 ret = tty_register_driver(ttyprintk_driver);
212 printk(KERN_ERR "Couldn't register ttyprintk driver\n");
219 put_tty_driver(ttyprintk_driver);
220 tty_port_destroy(&tpk_port.port);
224 static void __exit ttyprintk_exit(void)
226 tty_unregister_driver(ttyprintk_driver);
227 put_tty_driver(ttyprintk_driver);
228 tty_port_destroy(&tpk_port.port);
231 device_initcall(ttyprintk_init);
232 module_exit(ttyprintk_exit);
234 MODULE_LICENSE("GPL");