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/module.h>
  21
  22 struct ttyprintk_port {
  23         struct tty_port port;
  24         struct mutex port_write_mutex;
  25 };
  26
  27 static 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 fragmented, with '\'nl between fragments
  35  * - TPK_STR_SIZE isn't really the write_room limiting factor, because
  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 */
  40 static int tpk_curr;
  41
  42 static char tpk_buffer[TPK_STR_SIZE + 4];
  43
  44 static void tpk_flush(void)
  45 {
  46         if (tpk_curr > 0) {
  47                 tpk_buffer[tpk_curr] = '\0';
  48                 pr_info("[U] %s\n", tpk_buffer);
  49                 tpk_curr = 0;
  50         }
  51 }
  52
  53 static 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  */
  90 static 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  */
 100 static void tpk_close(struct tty_struct *tty, struct file *filp)
 101 {
 102         struct ttyprintk_port *tpkp = tty->driver_data;
 103
 104         mutex_lock(&tpkp->port_write_mutex);
 105         /* flush tpk_printk buffer */
 106         tpk_printk(NULL, 0);
 107         mutex_unlock(&tpkp->port_write_mutex);
 108
 109         tty_port_close(&tpkp->port, tty, filp);
 110 }
 111
 112 /*
 113  * TTY operations write function.
 114  */
 115 static int tpk_write(struct tty_struct *tty,
 116                 const unsigned char *buf, int count)
 117 {
 118         struct ttyprintk_port *tpkp = tty->driver_data;
 119         int ret;
 120
 121
 122         /* exclusive use of tpk_printk within this tty */
 123         mutex_lock(&tpkp->port_write_mutex);
 124         ret = tpk_printk(buf, count);
 125         mutex_unlock(&tpkp->port_write_mutex);
 126
 127         return ret;
 128 }
 129
 130 /*
 131  * TTY operations write_room function.
 132  */
 133 static int tpk_write_room(struct tty_struct *tty)
 134 {
 135         return TPK_MAX_ROOM;
 136 }
 137
 138 /*
 139  * TTY operations ioctl function.
 140  */
 141 static int tpk_ioctl(struct tty_struct *tty,
 142                         unsigned int cmd, unsigned long arg)
 143 {
 144         struct ttyprintk_port *tpkp = tty->driver_data;
 145
 146         if (!tpkp)
 147                 return -EINVAL;
 148
 149         switch (cmd) {
 150         /* Stop TIOCCONS */
 151         case TIOCCONS:
 152                 return -EOPNOTSUPP;
 153         default:
 154                 return -ENOIOCTLCMD;
 155         }
 156         return 0;
 157 }
 158
 159 static const struct tty_operations ttyprintk_ops = {
 160         .open = tpk_open,
 161         .close = tpk_close,
 162         .write = tpk_write,
 163         .write_room = tpk_write_room,
 164         .ioctl = tpk_ioctl,
 165 };
 166
 167 static const struct tty_port_operations null_ops = { };
 168
 169 static struct tty_driver *ttyprintk_driver;
 170
 171 static int __init ttyprintk_init(void)
 172 {
 173         int ret = -ENOMEM;
 174
 175         mutex_init(&tpk_port.port_write_mutex);
 176
 177         ttyprintk_driver = tty_alloc_driver(1,
 178                         TTY_DRIVER_RESET_TERMIOS |
 179                         TTY_DRIVER_REAL_RAW |
 180                         TTY_DRIVER_UNNUMBERED_NODE);
 181         if (IS_ERR(ttyprintk_driver))
 182                 return PTR_ERR(ttyprintk_driver);
 183
 184         tty_port_init(&tpk_port.port);
 185         tpk_port.port.ops = &null_ops;
 186
 187         ttyprintk_driver->driver_name = "ttyprintk";
 188         ttyprintk_driver->name = "ttyprintk";
 189         ttyprintk_driver->major = TTYAUX_MAJOR;
 190         ttyprintk_driver->minor_start = 3;
 191         ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
 192         ttyprintk_driver->init_termios = tty_std_termios;
 193         ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
 194         tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
 195         tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);
 196
 197         ret = tty_register_driver(ttyprintk_driver);
 198         if (ret < 0) {
 199                 printk(KERN_ERR "Couldn't register ttyprintk driver\n");
 200                 goto error;
 201         }
 202
 203         return 0;
 204
 205 error:
 206         put_tty_driver(ttyprintk_driver);
 207         tty_port_destroy(&tpk_port.port);
 208         return ret;
 209 }
 210
 211 static void __exit ttyprintk_exit(void)
 212 {
 213         tty_unregister_driver(ttyprintk_driver);
 214         put_tty_driver(ttyprintk_driver);
 215         tty_port_destroy(&tpk_port.port);
 216 }
 217
 218 device_initcall(ttyprintk_init);
 219 module_exit(ttyprintk_exit);
 220
 221 MODULE_LICENSE("GPL");