Root/drivers/char/ttyprintk.c

1/*
2 * linux/drivers/char/ttyprintk.c
3 *
4 * Copyright (C) 2010 Samo Pogacnik
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the smems of the GNU General Public License as published by
8 * the Free Software Foundation; version 2 of the License.
9 */
10
11/*
12 * This pseudo device allows user to make printk messages. It is possible
13 * to store "console" messages inline with kernel messages for better analyses
14 * of the boot process, for example.
15 */
16
17#include <linux/device.h>
18#include <linux/serial.h>
19#include <linux/tty.h>
20#include <linux/export.h>
21
22struct ttyprintk_port {
23    struct tty_port port;
24    struct mutex port_write_mutex;
25};
26
27static struct ttyprintk_port tpk_port;
28
29/*
30 * Our simple preformatting supports transparent output of (time-stamped)
31 * printk messages (also suitable for logging service):
32 * - any cr is replaced by nl
33 * - adds a ttyprintk source tag in front of each line
34 * - too long message is fragmeted, with '\'nl between fragments
35 * - TPK_STR_SIZE isn't really the write_room limiting factor, bcause
36 * it is emptied on the fly during preformatting.
37 */
38#define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
39#define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
40static const char *tpk_tag = "[U] "; /* U for User */
41static int tpk_curr;
42
43static int tpk_printk(const unsigned char *buf, int count)
44{
45    static char tmp[TPK_STR_SIZE + 4];
46    int i = tpk_curr;
47
48    if (buf == NULL) {
49        /* flush tmp[] */
50        if (tpk_curr > 0) {
51            /* non nl or cr terminated message - add nl */
52            tmp[tpk_curr + 0] = '\n';
53            tmp[tpk_curr + 1] = '\0';
54            printk(KERN_INFO "%s%s", tpk_tag, tmp);
55            tpk_curr = 0;
56        }
57        return i;
58    }
59
60    for (i = 0; i < count; i++) {
61        tmp[tpk_curr] = buf[i];
62        if (tpk_curr < TPK_STR_SIZE) {
63            switch (buf[i]) {
64            case '\r':
65                /* replace cr with nl */
66                tmp[tpk_curr + 0] = '\n';
67                tmp[tpk_curr + 1] = '\0';
68                printk(KERN_INFO "%s%s", tpk_tag, tmp);
69                tpk_curr = 0;
70                if ((i + 1) < count && buf[i + 1] == '\n')
71                    i++;
72                break;
73            case '\n':
74                tmp[tpk_curr + 1] = '\0';
75                printk(KERN_INFO "%s%s", tpk_tag, tmp);
76                tpk_curr = 0;
77                break;
78            default:
79                tpk_curr++;
80            }
81        } else {
82            /* end of tmp buffer reached: cut the message in two */
83            tmp[tpk_curr + 1] = '\\';
84            tmp[tpk_curr + 2] = '\n';
85            tmp[tpk_curr + 3] = '\0';
86            printk(KERN_INFO "%s%s", tpk_tag, tmp);
87            tpk_curr = 0;
88        }
89    }
90
91    return count;
92}
93
94/*
95 * TTY operations open function.
96 */
97static int tpk_open(struct tty_struct *tty, struct file *filp)
98{
99    tty->driver_data = &tpk_port;
100
101    return tty_port_open(&tpk_port.port, tty, filp);
102}
103
104/*
105 * TTY operations close function.
106 */
107static void tpk_close(struct tty_struct *tty, struct file *filp)
108{
109    struct ttyprintk_port *tpkp = tty->driver_data;
110
111    mutex_lock(&tpkp->port_write_mutex);
112    /* flush tpk_printk buffer */
113    tpk_printk(NULL, 0);
114    mutex_unlock(&tpkp->port_write_mutex);
115
116    tty_port_close(&tpkp->port, tty, filp);
117}
118
119/*
120 * TTY operations write function.
121 */
122static int tpk_write(struct tty_struct *tty,
123        const unsigned char *buf, int count)
124{
125    struct ttyprintk_port *tpkp = tty->driver_data;
126    int ret;
127
128
129    /* exclusive use of tpk_printk within this tty */
130    mutex_lock(&tpkp->port_write_mutex);
131    ret = tpk_printk(buf, count);
132    mutex_unlock(&tpkp->port_write_mutex);
133
134    return ret;
135}
136
137/*
138 * TTY operations write_room function.
139 */
140static int tpk_write_room(struct tty_struct *tty)
141{
142    return TPK_MAX_ROOM;
143}
144
145/*
146 * TTY operations ioctl function.
147 */
148static int tpk_ioctl(struct tty_struct *tty,
149            unsigned int cmd, unsigned long arg)
150{
151    struct ttyprintk_port *tpkp = tty->driver_data;
152
153    if (!tpkp)
154        return -EINVAL;
155
156    switch (cmd) {
157    /* Stop TIOCCONS */
158    case TIOCCONS:
159        return -EOPNOTSUPP;
160    default:
161        return -ENOIOCTLCMD;
162    }
163    return 0;
164}
165
166static const struct tty_operations ttyprintk_ops = {
167    .open = tpk_open,
168    .close = tpk_close,
169    .write = tpk_write,
170    .write_room = tpk_write_room,
171    .ioctl = tpk_ioctl,
172};
173
174static struct tty_port_operations null_ops = { };
175
176static struct tty_driver *ttyprintk_driver;
177
178static int __init ttyprintk_init(void)
179{
180    int ret = -ENOMEM;
181
182    tpk_port.port.ops = &null_ops;
183    mutex_init(&tpk_port.port_write_mutex);
184
185    ttyprintk_driver = tty_alloc_driver(1,
186            TTY_DRIVER_RESET_TERMIOS |
187            TTY_DRIVER_REAL_RAW |
188            TTY_DRIVER_UNNUMBERED_NODE);
189    if (IS_ERR(ttyprintk_driver))
190        return PTR_ERR(ttyprintk_driver);
191
192    tty_port_init(&tpk_port.port);
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    return 0;
211
212error:
213    tty_unregister_driver(ttyprintk_driver);
214    put_tty_driver(ttyprintk_driver);
215    tty_port_destroy(&tpk_port.port);
216    ttyprintk_driver = NULL;
217    return ret;
218}
219module_init(ttyprintk_init);
220

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