drivers/char/ttyprintk.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/drivers/char/ttyprintk.c
   4  *
   5  *  Copyright (C) 2010  Samo Pogacnik
   6  */
   7
   8 /*
   9  * This pseudo device allows user to make printk messages. It is possible
  10  * to store "console" messages inline with kernel messages for better analyses
  11  * of the boot process, for example.
  12  */
  13
  14 #include <linux/device.h>
  15 #include <linux/serial.h>
  16 #include <linux/tty.h>
  17 #include <linux/module.h>
  18
  19 struct ttyprintk_port {
  20         struct tty_port port;
  21         struct mutex port_write_mutex;
  22 };
  23
  24 static struct ttyprintk_port tpk_port;
  25
  26 /*
  27  * Our simple preformatting supports transparent output of (time-stamped)
  28  * printk messages (also suitable for logging service):
  29  * - any cr is replaced by nl
  30  * - adds a ttyprintk source tag in front of each line
  31  * - too long message is fragmented, with '\'nl between fragments
  32  * - TPK_STR_SIZE isn't really the write_room limiting factor, because
  33  *   it is emptied on the fly during preformatting.
  34  */
  35 #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
  36 #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
  37 #define TPK_PREFIX KERN_SOH __stringify(CONFIG_TTY_PRINTK_LEVEL)
  38
  39 static int tpk_curr;
  40
  41 static char tpk_buffer[TPK_STR_SIZE + 4];
  42
  43 static void tpk_flush(void)
  44 {
  45         if (tpk_curr > 0) {
  46                 tpk_buffer[tpk_curr] = '\0';
  47                 printk(TPK_PREFIX "[U] %s\n", tpk_buffer);
  48                 tpk_curr = 0;
  49         }
  50 }
  51
  52 static int tpk_printk(const unsigned char *buf, int count)
  53 {
  54         int i = tpk_curr;
  55
  56         if (buf == NULL) {
  57                 tpk_flush();
  58                 return i;
  59         }
  60
  61         for (i = 0; i < count; i++) {
  62                 if (tpk_curr >= TPK_STR_SIZE) {
  63                         /* end of tmp buffer reached: cut the message in two */
  64                         tpk_buffer[tpk_curr++] = '\\';
  65                         tpk_flush();
  66                 }
  67
  68                 switch (buf[i]) {
  69                 case '\r':
  70                         tpk_flush();
  71                         if ((i + 1) < count && buf[i + 1] == '\n')
  72                                 i++;
  73                         break;
  74                 case '\n':
  75                         tpk_flush();
  76                         break;
  77                 default:
  78                         tpk_buffer[tpk_curr++] = buf[i];
  79                         break;
  80                 }
  81         }
  82
  83         return count;
  84 }
  85
  86 /*
  87  * TTY operations open function.
  88  */
  89 static int tpk_open(struct tty_struct *tty, struct file *filp)
  90 {
  91         tty->driver_data = &tpk_port;
  92
  93         return tty_port_open(&tpk_port.port, tty, filp);
  94 }
  95
  96 /*
  97  * TTY operations close function.
  98  */
  99 static void tpk_close(struct tty_struct *tty, struct file *filp)
 100 {
 101         struct ttyprintk_port *tpkp = tty->driver_data;
 102
 103         mutex_lock(&tpkp->port_write_mutex);
 104         /* flush tpk_printk buffer */
 105         tpk_printk(NULL, 0);
 106         mutex_unlock(&tpkp->port_write_mutex);
 107
 108         tty_port_close(&tpkp->port, tty, filp);
 109 }
 110
 111 /*
 112  * TTY operations write function.
 113  */
 114 static int tpk_write(struct tty_struct *tty,
 115                 const unsigned char *buf, int count)
 116 {
 117         struct ttyprintk_port *tpkp = tty->driver_data;
 118         int ret;
 119
 120
 121         /* exclusive use of tpk_printk within this tty */
 122         mutex_lock(&tpkp->port_write_mutex);
 123         ret = tpk_printk(buf, count);
 124         mutex_unlock(&tpkp->port_write_mutex);
 125
 126         return ret;
 127 }
 128
 129 /*
 130  * TTY operations write_room function.
 131  */
 132 static int tpk_write_room(struct tty_struct *tty)
 133 {
 134         return TPK_MAX_ROOM;
 135 }
 136
 137 /*
 138  * TTY operations ioctl function.
 139  */
 140 static int tpk_ioctl(struct tty_struct *tty,
 141                         unsigned int cmd, unsigned long arg)
 142 {
 143         struct ttyprintk_port *tpkp = tty->driver_data;
 144
 145         if (!tpkp)
 146                 return -EINVAL;
 147
 148         switch (cmd) {
 149         /* Stop TIOCCONS */
 150         case TIOCCONS:
 151                 return -EOPNOTSUPP;
 152         default:
 153                 return -ENOIOCTLCMD;
 154         }
 155         return 0;
 156 }
 157
 158 static const struct tty_operations ttyprintk_ops = {
 159         .open = tpk_open,
 160         .close = tpk_close,
 161         .write = tpk_write,
 162         .write_room = tpk_write_room,
 163         .ioctl = tpk_ioctl,
 164 };
 165
 166 static const struct tty_port_operations null_ops = { };
 167
 168 static struct tty_driver *ttyprintk_driver;
 169
 170 static int __init ttyprintk_init(void)
 171 {
 172         int ret = -ENOMEM;
 173
 174         mutex_init(&tpk_port.port_write_mutex);
 175
 176         ttyprintk_driver = tty_alloc_driver(1,
 177                         TTY_DRIVER_RESET_TERMIOS |
 178                         TTY_DRIVER_REAL_RAW |
 179                         TTY_DRIVER_UNNUMBERED_NODE);
 180         if (IS_ERR(ttyprintk_driver))
 181                 return PTR_ERR(ttyprintk_driver);
 182
 183         tty_port_init(&tpk_port.port);
 184         tpk_port.port.ops = &null_ops;
 185
 186         ttyprintk_driver->driver_name = "ttyprintk";
 187         ttyprintk_driver->name = "ttyprintk";
 188         ttyprintk_driver->major = TTYAUX_MAJOR;
 189         ttyprintk_driver->minor_start = 3;
 190         ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
 191         ttyprintk_driver->init_termios = tty_std_termios;
 192         ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
 193         tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
 194         tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);
 195
 196         ret = tty_register_driver(ttyprintk_driver);
 197         if (ret < 0) {
 198                 printk(KERN_ERR "Couldn't register ttyprintk driver\n");
 199                 goto error;
 200         }
 201
 202         return 0;
 203
 204 error:
 205         put_tty_driver(ttyprintk_driver);
 206         tty_port_destroy(&tpk_port.port);
 207         return ret;
 208 }
 209
 210 static void __exit ttyprintk_exit(void)
 211 {
 212         tty_unregister_driver(ttyprintk_driver);
 213         put_tty_driver(ttyprintk_driver);
 214         tty_port_destroy(&tpk_port.port);
 215 }
 216
 217 device_initcall(ttyprintk_init);
 218 module_exit(ttyprintk_exit);
 219
 220 MODULE_LICENSE("GPL");