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