linux/drivers/char/ttyprintk.c
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   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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