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 #include <linux/spinlock.h>
  19
  20 struct ttyprintk_port {
  21         struct tty_port port;
  22         spinlock_t spinlock;
  23 };
  24
  25 static struct ttyprintk_port tpk_port;
  26
  27 /*
  28  * Our simple preformatting supports transparent output of (time-stamped)
  29  * printk messages (also suitable for logging service):
  30  * - any cr is replaced by nl
  31  * - adds a ttyprintk source tag in front of each line
  32  * - too long message is fragmented, with '\'nl between fragments
  33  * - TPK_STR_SIZE isn't really the write_room limiting factor, because
  34  *   it is emptied on the fly during preformatting.
  35  */
  36 #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
  37 #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
  38 #define TPK_PREFIX KERN_SOH __stringify(CONFIG_TTY_PRINTK_LEVEL)
  39
  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                 printk(TPK_PREFIX "[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;
  56
  57         for (i = 0; i < count; i++) {
  58                 if (tpk_curr >= TPK_STR_SIZE) {
  59                         /* end of tmp buffer reached: cut the message in two */
  60                         tpk_buffer[tpk_curr++] = '\\';
  61                         tpk_flush();
  62                 }
  63
  64                 switch (buf[i]) {
  65                 case '\r':
  66                         tpk_flush();
  67                         if ((i + 1) < count && buf[i + 1] == '\n')
  68                                 i++;
  69                         break;
  70                 case '\n':
  71                         tpk_flush();
  72                         break;
  73                 default:
  74                         tpk_buffer[tpk_curr++] = buf[i];
  75                         break;
  76                 }
  77         }
  78
  79         return count;
  80 }
  81
  82 /*
  83  * TTY operations open function.
  84  */
  85 static int tpk_open(struct tty_struct *tty, struct file *filp)
  86 {
  87         tty->driver_data = &tpk_port;
  88
  89         return tty_port_open(&tpk_port.port, tty, filp);
  90 }
  91
  92 /*
  93  * TTY operations close function.
  94  */
  95 static void tpk_close(struct tty_struct *tty, struct file *filp)
  96 {
  97         struct ttyprintk_port *tpkp = tty->driver_data;
  98
  99         tty_port_close(&tpkp->port, tty, filp);
 100 }
 101
 102 /*
 103  * TTY operations write function.
 104  */
 105 static int tpk_write(struct tty_struct *tty,
 106                 const unsigned char *buf, int count)
 107 {
 108         struct ttyprintk_port *tpkp = tty->driver_data;
 109         unsigned long flags;
 110         int ret;
 111
 112         /* exclusive use of tpk_printk within this tty */
 113         spin_lock_irqsave(&tpkp->spinlock, flags);
 114         ret = tpk_printk(buf, count);
 115         spin_unlock_irqrestore(&tpkp->spinlock, flags);
 116
 117         return ret;
 118 }
 119
 120 /*
 121  * TTY operations write_room function.
 122  */
 123 static unsigned int tpk_write_room(struct tty_struct *tty)
 124 {
 125         return TPK_MAX_ROOM;
 126 }
 127
 128 /*
 129  * TTY operations hangup function.
 130  */
 131 static void tpk_hangup(struct tty_struct *tty)
 132 {
 133         struct ttyprintk_port *tpkp = tty->driver_data;
 134
 135         tty_port_hangup(&tpkp->port);
 136 }
 137
 138 /*
 139  * TTY port operations shutdown function.
 140  */
 141 static void tpk_port_shutdown(struct tty_port *tport)
 142 {
 143         struct ttyprintk_port *tpkp =
 144                 container_of(tport, struct ttyprintk_port, port);
 145         unsigned long flags;
 146
 147         spin_lock_irqsave(&tpkp->spinlock, flags);
 148         tpk_flush();
 149         spin_unlock_irqrestore(&tpkp->spinlock, flags);
 150 }
 151
 152 static const struct tty_operations ttyprintk_ops = {
 153         .open = tpk_open,
 154         .close = tpk_close,
 155         .write = tpk_write,
 156         .write_room = tpk_write_room,
 157         .hangup = tpk_hangup,
 158 };
 159
 160 static const struct tty_port_operations tpk_port_ops = {
 161         .shutdown = tpk_port_shutdown,
 162 };
 163
 164 static struct tty_driver *ttyprintk_driver;
 165
 166 static int __init ttyprintk_init(void)
 167 {
 168         int ret;
 169
 170         spin_lock_init(&tpk_port.spinlock);
 171
 172         ttyprintk_driver = tty_alloc_driver(1,
 173                         TTY_DRIVER_RESET_TERMIOS |
 174                         TTY_DRIVER_REAL_RAW |
 175                         TTY_DRIVER_UNNUMBERED_NODE);
 176         if (IS_ERR(ttyprintk_driver))
 177                 return PTR_ERR(ttyprintk_driver);
 178
 179         tty_port_init(&tpk_port.port);
 180         tpk_port.port.ops = &tpk_port_ops;
 181
 182         ttyprintk_driver->driver_name = "ttyprintk";
 183         ttyprintk_driver->name = "ttyprintk";
 184         ttyprintk_driver->major = TTYAUX_MAJOR;
 185         ttyprintk_driver->minor_start = 3;
 186         ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
 187         ttyprintk_driver->init_termios = tty_std_termios;
 188         ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
 189         tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
 190         tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);
 191
 192         ret = tty_register_driver(ttyprintk_driver);
 193         if (ret < 0) {
 194                 printk(KERN_ERR "Couldn't register ttyprintk driver\n");
 195                 goto error;
 196         }
 197
 198         return 0;
 199
 200 error:
 201         tty_driver_kref_put(ttyprintk_driver);
 202         tty_port_destroy(&tpk_port.port);
 203         return ret;
 204 }
 205
 206 static void __exit ttyprintk_exit(void)
 207 {
 208         tty_unregister_driver(ttyprintk_driver);
 209         tty_driver_kref_put(ttyprintk_driver);
 210         tty_port_destroy(&tpk_port.port);
 211 }
 212
 213 device_initcall(ttyprintk_init);
 214 module_exit(ttyprintk_exit);
 215
 216 MODULE_LICENSE("GPL");