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/console.h>
  15 #include <linux/device.h>
  16 #include <linux/serial.h>
  17 #include <linux/tty.h>
  18 #include <linux/module.h>
  19 #include <linux/spinlock.h>
  20
  21 struct ttyprintk_port {
  22         struct tty_port port;
  23         spinlock_t spinlock;
  24 };
  25
  26 static struct ttyprintk_port tpk_port;
  27
  28 /*
  29  * Our simple preformatting supports transparent output of (time-stamped)
  30  * printk messages (also suitable for logging service):
  31  * - any cr is replaced by nl
  32  * - adds a ttyprintk source tag in front of each line
  33  * - too long message is fragmented, with '\'nl between fragments
  34  * - TPK_STR_SIZE isn't really the write_room limiting factor, because
  35  *   it is emptied on the fly during preformatting.
  36  */
  37 #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
  38 #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
  39 #define TPK_PREFIX KERN_SOH __stringify(CONFIG_TTY_PRINTK_LEVEL)
  40
  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                 printk(TPK_PREFIX "[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;
  57
  58         for (i = 0; i < count; i++) {
  59                 if (tpk_curr >= TPK_STR_SIZE) {
  60                         /* end of tmp buffer reached: cut the message in two */
  61                         tpk_buffer[tpk_curr++] = '\\';
  62                         tpk_flush();
  63                 }
  64
  65                 switch (buf[i]) {
  66                 case '\r':
  67                         tpk_flush();
  68                         if ((i + 1) < count && buf[i + 1] == '\n')
  69                                 i++;
  70                         break;
  71                 case '\n':
  72                         tpk_flush();
  73                         break;
  74                 default:
  75                         tpk_buffer[tpk_curr++] = buf[i];
  76                         break;
  77                 }
  78         }
  79
  80         return count;
  81 }
  82
  83 /*
  84  * TTY operations open function.
  85  */
  86 static int tpk_open(struct tty_struct *tty, struct file *filp)
  87 {
  88         tty->driver_data = &tpk_port;
  89
  90         return tty_port_open(&tpk_port.port, tty, filp);
  91 }
  92
  93 /*
  94  * TTY operations close function.
  95  */
  96 static void tpk_close(struct tty_struct *tty, struct file *filp)
  97 {
  98         struct ttyprintk_port *tpkp = tty->driver_data;
  99
 100         tty_port_close(&tpkp->port, tty, filp);
 101 }
 102
 103 /*
 104  * TTY operations write function.
 105  */
 106 static int tpk_write(struct tty_struct *tty,
 107                 const unsigned char *buf, int count)
 108 {
 109         struct ttyprintk_port *tpkp = tty->driver_data;
 110         unsigned long flags;
 111         int ret;
 112
 113         /* exclusive use of tpk_printk within this tty */
 114         spin_lock_irqsave(&tpkp->spinlock, flags);
 115         ret = tpk_printk(buf, count);
 116         spin_unlock_irqrestore(&tpkp->spinlock, flags);
 117
 118         return ret;
 119 }
 120
 121 /*
 122  * TTY operations write_room function.
 123  */
 124 static unsigned int tpk_write_room(struct tty_struct *tty)
 125 {
 126         return TPK_MAX_ROOM;
 127 }
 128
 129 /*
 130  * TTY operations hangup function.
 131  */
 132 static void tpk_hangup(struct tty_struct *tty)
 133 {
 134         struct ttyprintk_port *tpkp = tty->driver_data;
 135
 136         tty_port_hangup(&tpkp->port);
 137 }
 138
 139 /*
 140  * TTY port operations shutdown function.
 141  */
 142 static void tpk_port_shutdown(struct tty_port *tport)
 143 {
 144         struct ttyprintk_port *tpkp =
 145                 container_of(tport, struct ttyprintk_port, port);
 146         unsigned long flags;
 147
 148         spin_lock_irqsave(&tpkp->spinlock, flags);
 149         tpk_flush();
 150         spin_unlock_irqrestore(&tpkp->spinlock, flags);
 151 }
 152
 153 static const struct tty_operations ttyprintk_ops = {
 154         .open = tpk_open,
 155         .close = tpk_close,
 156         .write = tpk_write,
 157         .write_room = tpk_write_room,
 158         .hangup = tpk_hangup,
 159 };
 160
 161 static const struct tty_port_operations tpk_port_ops = {
 162         .shutdown = tpk_port_shutdown,
 163 };
 164
 165 static struct tty_driver *ttyprintk_driver;
 166
 167 static struct tty_driver *ttyprintk_console_device(struct console *c,
 168                                                    int *index)
 169 {
 170         *index = 0;
 171         return ttyprintk_driver;
 172 }
 173
 174 static struct console ttyprintk_console = {
 175         .name = "ttyprintk",
 176         .device = ttyprintk_console_device,
 177 };
 178
 179 static int __init ttyprintk_init(void)
 180 {
 181         int ret;
 182
 183         spin_lock_init(&tpk_port.spinlock);
 184
 185         ttyprintk_driver = tty_alloc_driver(1,
 186                         TTY_DRIVER_RESET_TERMIOS |
 187                         TTY_DRIVER_REAL_RAW |
 188                         TTY_DRIVER_UNNUMBERED_NODE);
 189         if (IS_ERR(ttyprintk_driver))
 190                 return PTR_ERR(ttyprintk_driver);
 191
 192         tty_port_init(&tpk_port.port);
 193         tpk_port.port.ops = &tpk_port_ops;
 194
 195         ttyprintk_driver->driver_name = "ttyprintk";
 196         ttyprintk_driver->name = "ttyprintk";
 197         ttyprintk_driver->major = TTYAUX_MAJOR;
 198         ttyprintk_driver->minor_start = 3;
 199         ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
 200         ttyprintk_driver->init_termios = tty_std_termios;
 201         ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
 202         tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
 203         tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);
 204
 205         ret = tty_register_driver(ttyprintk_driver);
 206         if (ret < 0) {
 207                 printk(KERN_ERR "Couldn't register ttyprintk driver\n");
 208                 goto error;
 209         }
 210
 211         register_console(&ttyprintk_console);
 212
 213         return 0;
 214
 215 error:
 216         tty_driver_kref_put(ttyprintk_driver);
 217         tty_port_destroy(&tpk_port.port);
 218         return ret;
 219 }
 220
 221 static void __exit ttyprintk_exit(void)
 222 {
 223         unregister_console(&ttyprintk_console);
 224         tty_unregister_driver(ttyprintk_driver);
 225         tty_driver_kref_put(ttyprintk_driver);
 226         tty_port_destroy(&tpk_port.port);
 227 }
 228
 229 device_initcall(ttyprintk_init);
 230 module_exit(ttyprintk_exit);
 231
 232 MODULE_LICENSE("GPL");