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 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 */
  40 static const char *tpk_tag = "[U] "; /* U for User */
  41 static int tpk_curr;
  42
  43 static 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  */
  97 static 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  */
 107 static 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  */
 122 static 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  */
 140 static int tpk_write_room(struct tty_struct *tty)
 141 {
 142         return TPK_MAX_ROOM;
 143 }
 144
 145 /*
 146  * TTY operations ioctl function.
 147  */
 148 static 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
 166 static 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
 174 static const struct tty_port_operations null_ops = { };
 175
 176 static struct tty_driver *ttyprintk_driver;
 177
 178 static int __init ttyprintk_init(void)
 179 {
 180         int ret = -ENOMEM;
 181
 182         mutex_init(&tpk_port.port_write_mutex);
 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 = &null_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         return 0;
 211
 212 error:
 213         put_tty_driver(ttyprintk_driver);
 214         tty_port_destroy(&tpk_port.port);
 215         return ret;
 216 }
 217
 218 static void __exit ttyprintk_exit(void)
 219 {
 220         tty_unregister_driver(ttyprintk_driver);
 221         put_tty_driver(ttyprintk_driver);
 222         tty_port_destroy(&tpk_port.port);
 223 }
 224
 225 device_initcall(ttyprintk_init);
 226 module_exit(ttyprintk_exit);
 227
 228 MODULE_LICENSE("GPL");