1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 *  linux/drivers/char/ttyprintk.c
4 *
5 *  Copyright (C) 2010  Samo Pogacnik
6 */
7
8/*
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.
12 */
13
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>
19
20struct ttyprintk_port {
21	struct tty_port port;
22	spinlock_t spinlock;
23};
24
25static struct ttyprintk_port tpk_port;
26
27/*
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.
35 */
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)
39
40static int tpk_curr;
41
42static char tpk_buffer[TPK_STR_SIZE + 4];
43
44static void tpk_flush(void)
45{
46	if (tpk_curr > 0) {
47		tpk_buffer[tpk_curr] = '\0';
48		printk(TPK_PREFIX "[U] %s\n", tpk_buffer);
49		tpk_curr = 0;
50	}
51}
52
53static int tpk_printk(const unsigned char *buf, int count)
54{
55	int i = tpk_curr;
56
57	if (buf == NULL) {
58		tpk_flush();
59		return i;
60	}
61
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++] = '\\';
66			tpk_flush();
67		}
68
69		switch (buf[i]) {
70		case '\r':
71			tpk_flush();
72			if ((i + 1) < count && buf[i + 1] == '\n')
73				i++;
74			break;
75		case '\n':
76			tpk_flush();
77			break;
78		default:
79			tpk_buffer[tpk_curr++] = buf[i];
80			break;
81		}
82	}
83
84	return count;
85}
86
87/*
88 * TTY operations open function.
89 */
90static int tpk_open(struct tty_struct *tty, struct file *filp)
91{
92	tty->driver_data = &tpk_port;
93
94	return tty_port_open(&tpk_port.port, tty, filp);
95}
96
97/*
98 * TTY operations close function.
99 */
100static void tpk_close(struct tty_struct *tty, struct file *filp)
101{
102	struct ttyprintk_port *tpkp = tty->driver_data;
103	unsigned long flags;
104
105	spin_lock_irqsave(&tpkp->spinlock, flags);
106	/* flush tpk_printk buffer */
107	tpk_printk(NULL, 0);
108	spin_unlock_irqrestore(&tpkp->spinlock, flags);
109
110	tty_port_close(&tpkp->port, tty, filp);
111}
112
113/*
114 * TTY operations write function.
115 */
116static int tpk_write(struct tty_struct *tty,
117		const unsigned char *buf, int count)
118{
119	struct ttyprintk_port *tpkp = tty->driver_data;
120	unsigned long flags;
121	int ret;
122
123
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);
128
129	return ret;
130}
131
132/*
133 * TTY operations write_room function.
134 */
135static int tpk_write_room(struct tty_struct *tty)
136{
137	return TPK_MAX_ROOM;
138}
139
140/*
141 * TTY operations ioctl function.
142 */
143static int tpk_ioctl(struct tty_struct *tty,
144			unsigned int cmd, unsigned long arg)
145{
146	struct ttyprintk_port *tpkp = tty->driver_data;
147
148	if (!tpkp)
149		return -EINVAL;
150
151	switch (cmd) {
152	/* Stop TIOCCONS */
153	case TIOCCONS:
154		return -EOPNOTSUPP;
155	default:
156		return -ENOIOCTLCMD;
157	}
158	return 0;
159}
160
161/*
162 * TTY operations hangup function.
163 */
164static void tpk_hangup(struct tty_struct *tty)
165{
166	struct ttyprintk_port *tpkp = tty->driver_data;
167
168	tty_port_hangup(&tpkp->port);
169}
170
171static const struct tty_operations ttyprintk_ops = {
172	.open = tpk_open,
173	.close = tpk_close,
174	.write = tpk_write,
175	.write_room = tpk_write_room,
176	.ioctl = tpk_ioctl,
177	.hangup = tpk_hangup,
178};
179
180static const struct tty_port_operations null_ops = { };
181
182static struct tty_driver *ttyprintk_driver;
183
184static int __init ttyprintk_init(void)
185{
186	int ret;
187
188	spin_lock_init(&tpk_port.spinlock);
189
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);
196
197	tty_port_init(&tpk_port.port);
198	tpk_port.port.ops = &null_ops;
199
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);
209
210	ret = tty_register_driver(ttyprintk_driver);
211	if (ret < 0) {
212		printk(KERN_ERR "Couldn't register ttyprintk driver\n");
213		goto error;
214	}
215
216	return 0;
217
218error:
219	put_tty_driver(ttyprintk_driver);
220	tty_port_destroy(&tpk_port.port);
221	return ret;
222}
223
224static void __exit ttyprintk_exit(void)
225{
226	tty_unregister_driver(ttyprintk_driver);
227	put_tty_driver(ttyprintk_driver);
228	tty_port_destroy(&tpk_port.port);
229}
230
231device_initcall(ttyprintk_init);
232module_exit(ttyprintk_exit);
233
234MODULE_LICENSE("GPL");
235