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
19 struct ttyprintk_port {
20 struct tty_port port;
21 struct mutex port_write_mutex;
22 };
23
24 static struct ttyprintk_port tpk_port;
25
26 /*
27 * Our simple preformatting supports transparent output of (time-stamped)
28 * printk messages (also suitable for logging service):
29 * - any cr is replaced by nl
30 * - adds a ttyprintk source tag in front of each line
31 * - too long message is fragmented, with '\'nl between fragments
32 * - TPK_STR_SIZE isn't really the write_room limiting factor, because
33 * it is emptied on the fly during preformatting.
34 */
35 #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
36 #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
37 #define TPK_PREFIX KERN_SOH __stringify(CONFIG_TTY_PRINTK_LEVEL)
38
39 static int tpk_curr;
40
41 static char tpk_buffer[TPK_STR_SIZE + 4];
42
tpk_flush(void)43 static void tpk_flush(void)
44 {
45 if (tpk_curr > 0) {
46 tpk_buffer[tpk_curr] = '\0';
47 printk(TPK_PREFIX "[U] %s\n", tpk_buffer);
48 tpk_curr = 0;
49 }
50 }
51
tpk_printk(const unsigned char * buf,int count)52 static int tpk_printk(const unsigned char *buf, int count)
53 {
54 int i = tpk_curr;
55
56 if (buf == NULL) {
57 tpk_flush();
58 return i;
59 }
60
61 for (i = 0; i < count; i++) {
62 if (tpk_curr >= TPK_STR_SIZE) {
63 /* end of tmp buffer reached: cut the message in two */
64 tpk_buffer[tpk_curr++] = '\\';
65 tpk_flush();
66 }
67
68 switch (buf[i]) {
69 case '\r':
70 tpk_flush();
71 if ((i + 1) < count && buf[i + 1] == '\n')
72 i++;
73 break;
74 case '\n':
75 tpk_flush();
76 break;
77 default:
78 tpk_buffer[tpk_curr++] = buf[i];
79 break;
80 }
81 }
82
83 return count;
84 }
85
86 /*
87 * TTY operations open function.
88 */
tpk_open(struct tty_struct * tty,struct file * filp)89 static int tpk_open(struct tty_struct *tty, struct file *filp)
90 {
91 tty->driver_data = &tpk_port;
92
93 return tty_port_open(&tpk_port.port, tty, filp);
94 }
95
96 /*
97 * TTY operations close function.
98 */
tpk_close(struct tty_struct * tty,struct file * filp)99 static void tpk_close(struct tty_struct *tty, struct file *filp)
100 {
101 struct ttyprintk_port *tpkp = tty->driver_data;
102
103 mutex_lock(&tpkp->port_write_mutex);
104 /* flush tpk_printk buffer */
105 tpk_printk(NULL, 0);
106 mutex_unlock(&tpkp->port_write_mutex);
107
108 tty_port_close(&tpkp->port, tty, filp);
109 }
110
111 /*
112 * TTY operations write function.
113 */
tpk_write(struct tty_struct * tty,const unsigned char * buf,int count)114 static int tpk_write(struct tty_struct *tty,
115 const unsigned char *buf, int count)
116 {
117 struct ttyprintk_port *tpkp = tty->driver_data;
118 int ret;
119
120
121 /* exclusive use of tpk_printk within this tty */
122 mutex_lock(&tpkp->port_write_mutex);
123 ret = tpk_printk(buf, count);
124 mutex_unlock(&tpkp->port_write_mutex);
125
126 return ret;
127 }
128
129 /*
130 * TTY operations write_room function.
131 */
tpk_write_room(struct tty_struct * tty)132 static int tpk_write_room(struct tty_struct *tty)
133 {
134 return TPK_MAX_ROOM;
135 }
136
137 /*
138 * TTY operations ioctl function.
139 */
tpk_ioctl(struct tty_struct * tty,unsigned int cmd,unsigned long arg)140 static int tpk_ioctl(struct tty_struct *tty,
141 unsigned int cmd, unsigned long arg)
142 {
143 struct ttyprintk_port *tpkp = tty->driver_data;
144
145 if (!tpkp)
146 return -EINVAL;
147
148 switch (cmd) {
149 /* Stop TIOCCONS */
150 case TIOCCONS:
151 return -EOPNOTSUPP;
152 default:
153 return -ENOIOCTLCMD;
154 }
155 return 0;
156 }
157
158 static const struct tty_operations ttyprintk_ops = {
159 .open = tpk_open,
160 .close = tpk_close,
161 .write = tpk_write,
162 .write_room = tpk_write_room,
163 .ioctl = tpk_ioctl,
164 };
165
166 static const struct tty_port_operations null_ops = { };
167
168 static struct tty_driver *ttyprintk_driver;
169
ttyprintk_init(void)170 static int __init ttyprintk_init(void)
171 {
172 int ret = -ENOMEM;
173
174 mutex_init(&tpk_port.port_write_mutex);
175
176 ttyprintk_driver = tty_alloc_driver(1,
177 TTY_DRIVER_RESET_TERMIOS |
178 TTY_DRIVER_REAL_RAW |
179 TTY_DRIVER_UNNUMBERED_NODE);
180 if (IS_ERR(ttyprintk_driver))
181 return PTR_ERR(ttyprintk_driver);
182
183 tty_port_init(&tpk_port.port);
184 tpk_port.port.ops = &null_ops;
185
186 ttyprintk_driver->driver_name = "ttyprintk";
187 ttyprintk_driver->name = "ttyprintk";
188 ttyprintk_driver->major = TTYAUX_MAJOR;
189 ttyprintk_driver->minor_start = 3;
190 ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
191 ttyprintk_driver->init_termios = tty_std_termios;
192 ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
193 tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
194 tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);
195
196 ret = tty_register_driver(ttyprintk_driver);
197 if (ret < 0) {
198 printk(KERN_ERR "Couldn't register ttyprintk driver\n");
199 goto error;
200 }
201
202 return 0;
203
204 error:
205 put_tty_driver(ttyprintk_driver);
206 tty_port_destroy(&tpk_port.port);
207 return ret;
208 }
209
ttyprintk_exit(void)210 static void __exit ttyprintk_exit(void)
211 {
212 tty_unregister_driver(ttyprintk_driver);
213 put_tty_driver(ttyprintk_driver);
214 tty_port_destroy(&tpk_port.port);
215 }
216
217 device_initcall(ttyprintk_init);
218 module_exit(ttyprintk_exit);
219
220 MODULE_LICENSE("GPL");
221