xref: /linux/drivers/char/ttyprintk.c (revision a1ff5a7d78a036d6c2178ee5acd6ba4946243800)
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/console.h>
15 #include <linux/device.h>
16 #include <linux/serial.h>
17 #include <linux/tty.h>
18 #include <linux/module.h>
19 #include <linux/spinlock.h>
20 
21 struct ttyprintk_port {
22 	struct tty_port port;
23 	spinlock_t spinlock;
24 };
25 
26 static struct ttyprintk_port tpk_port;
27 
28 /*
29  * Our simple preformatting supports transparent output of (time-stamped)
30  * printk messages (also suitable for logging service):
31  * - any cr is replaced by nl
32  * - adds a ttyprintk source tag in front of each line
33  * - too long message is fragmented, with '\'nl between fragments
34  * - TPK_STR_SIZE isn't really the write_room limiting factor, because
35  *   it is emptied on the fly during preformatting.
36  */
37 #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
38 #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
39 #define TPK_PREFIX KERN_SOH __stringify(CONFIG_TTY_PRINTK_LEVEL)
40 
41 static int tpk_curr;
42 
43 static u8 tpk_buffer[TPK_STR_SIZE + 4];
44 
tpk_flush(void)45 static void tpk_flush(void)
46 {
47 	if (tpk_curr > 0) {
48 		tpk_buffer[tpk_curr] = '\0';
49 		printk(TPK_PREFIX "[U] %s\n", tpk_buffer);
50 		tpk_curr = 0;
51 	}
52 }
53 
tpk_printk(const u8 * buf,size_t count)54 static int tpk_printk(const u8 *buf, size_t count)
55 {
56 	size_t i;
57 
58 	for (i = 0; i < count; i++) {
59 		if (tpk_curr >= TPK_STR_SIZE) {
60 			/* end of tmp buffer reached: cut the message in two */
61 			tpk_buffer[tpk_curr++] = '\\';
62 			tpk_flush();
63 		}
64 
65 		switch (buf[i]) {
66 		case '\r':
67 			tpk_flush();
68 			if ((i + 1) < count && buf[i + 1] == '\n')
69 				i++;
70 			break;
71 		case '\n':
72 			tpk_flush();
73 			break;
74 		default:
75 			tpk_buffer[tpk_curr++] = buf[i];
76 			break;
77 		}
78 	}
79 
80 	return count;
81 }
82 
83 /*
84  * TTY operations open function.
85  */
tpk_open(struct tty_struct * tty,struct file * filp)86 static int tpk_open(struct tty_struct *tty, struct file *filp)
87 {
88 	tty->driver_data = &tpk_port;
89 
90 	return tty_port_open(&tpk_port.port, tty, filp);
91 }
92 
93 /*
94  * TTY operations close function.
95  */
tpk_close(struct tty_struct * tty,struct file * filp)96 static void tpk_close(struct tty_struct *tty, struct file *filp)
97 {
98 	struct ttyprintk_port *tpkp = tty->driver_data;
99 
100 	tty_port_close(&tpkp->port, tty, filp);
101 }
102 
103 /*
104  * TTY operations write function.
105  */
tpk_write(struct tty_struct * tty,const u8 * buf,size_t count)106 static ssize_t tpk_write(struct tty_struct *tty, const u8 *buf, size_t count)
107 {
108 	struct ttyprintk_port *tpkp = tty->driver_data;
109 	unsigned long flags;
110 	int ret;
111 
112 	/* exclusive use of tpk_printk within this tty */
113 	spin_lock_irqsave(&tpkp->spinlock, flags);
114 	ret = tpk_printk(buf, count);
115 	spin_unlock_irqrestore(&tpkp->spinlock, flags);
116 
117 	return ret;
118 }
119 
120 /*
121  * TTY operations write_room function.
122  */
tpk_write_room(struct tty_struct * tty)123 static unsigned int tpk_write_room(struct tty_struct *tty)
124 {
125 	return TPK_MAX_ROOM;
126 }
127 
128 /*
129  * TTY operations hangup function.
130  */
tpk_hangup(struct tty_struct * tty)131 static void tpk_hangup(struct tty_struct *tty)
132 {
133 	struct ttyprintk_port *tpkp = tty->driver_data;
134 
135 	tty_port_hangup(&tpkp->port);
136 }
137 
138 /*
139  * TTY port operations shutdown function.
140  */
tpk_port_shutdown(struct tty_port * tport)141 static void tpk_port_shutdown(struct tty_port *tport)
142 {
143 	struct ttyprintk_port *tpkp =
144 		container_of(tport, struct ttyprintk_port, port);
145 	unsigned long flags;
146 
147 	spin_lock_irqsave(&tpkp->spinlock, flags);
148 	tpk_flush();
149 	spin_unlock_irqrestore(&tpkp->spinlock, flags);
150 }
151 
152 static const struct tty_operations ttyprintk_ops = {
153 	.open = tpk_open,
154 	.close = tpk_close,
155 	.write = tpk_write,
156 	.write_room = tpk_write_room,
157 	.hangup = tpk_hangup,
158 };
159 
160 static const struct tty_port_operations tpk_port_ops = {
161 	.shutdown = tpk_port_shutdown,
162 };
163 
164 static struct tty_driver *ttyprintk_driver;
165 
ttyprintk_console_device(struct console * c,int * index)166 static struct tty_driver *ttyprintk_console_device(struct console *c,
167 						   int *index)
168 {
169 	*index = 0;
170 	return ttyprintk_driver;
171 }
172 
173 static struct console ttyprintk_console = {
174 	.name = "ttyprintk",
175 	.device = ttyprintk_console_device,
176 };
177 
ttyprintk_init(void)178 static int __init ttyprintk_init(void)
179 {
180 	int ret;
181 
182 	spin_lock_init(&tpk_port.spinlock);
183 
184 	ttyprintk_driver = tty_alloc_driver(1,
185 			TTY_DRIVER_RESET_TERMIOS |
186 			TTY_DRIVER_REAL_RAW |
187 			TTY_DRIVER_UNNUMBERED_NODE);
188 	if (IS_ERR(ttyprintk_driver))
189 		return PTR_ERR(ttyprintk_driver);
190 
191 	tty_port_init(&tpk_port.port);
192 	tpk_port.port.ops = &tpk_port_ops;
193 
194 	ttyprintk_driver->driver_name = "ttyprintk";
195 	ttyprintk_driver->name = "ttyprintk";
196 	ttyprintk_driver->major = TTYAUX_MAJOR;
197 	ttyprintk_driver->minor_start = 3;
198 	ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
199 	ttyprintk_driver->init_termios = tty_std_termios;
200 	ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
201 	tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
202 	tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);
203 
204 	ret = tty_register_driver(ttyprintk_driver);
205 	if (ret < 0) {
206 		printk(KERN_ERR "Couldn't register ttyprintk driver\n");
207 		goto error;
208 	}
209 
210 	register_console(&ttyprintk_console);
211 
212 	return 0;
213 
214 error:
215 	tty_driver_kref_put(ttyprintk_driver);
216 	tty_port_destroy(&tpk_port.port);
217 	return ret;
218 }
219 
ttyprintk_exit(void)220 static void __exit ttyprintk_exit(void)
221 {
222 	unregister_console(&ttyprintk_console);
223 	tty_unregister_driver(ttyprintk_driver);
224 	tty_driver_kref_put(ttyprintk_driver);
225 	tty_port_destroy(&tpk_port.port);
226 }
227 
228 device_initcall(ttyprintk_init);
229 module_exit(ttyprintk_exit);
230 
231 MODULE_DESCRIPTION("TTY driver to output user messages via printk");
232 MODULE_LICENSE("GPL");
233