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 u8 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 u8 *buf, size_t count)
  55 {
  56         size_t 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 ssize_t tpk_write(struct tty_struct *tty, const u8 *buf, size_t 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 struct tty_driver *ttyprintk_console_device(struct console *c,
 167                                                    int *index)
 168 {
 169         *index = 0;
 170         return ttyprintk_driver;
 171 }
 172
 173 static struct console ttyprintk_console = {
 174         .name = "ttyprintk",
 175         .device = ttyprintk_console_device,
 176 };
 177
 178 static int __init ttyprintk_init(void)
 179 {
 180         int ret;
 181
 182         spin_lock_init(&tpk_port.spinlock);
 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 = &tpk_port_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         register_console(&ttyprintk_console);
 211
 212         return 0;
 213
 214 error:
 215         tty_driver_kref_put(ttyprintk_driver);
 216         tty_port_destroy(&tpk_port.port);
 217         return ret;
 218 }
 219
 220 static void __exit ttyprintk_exit(void)
 221 {
 222         unregister_console(&ttyprintk_console);
 223         tty_unregister_driver(ttyprintk_driver);
 224         tty_driver_kref_put(ttyprintk_driver);
 225         tty_port_destroy(&tpk_port.port);
 226 }
 227
 228 device_initcall(ttyprintk_init);
 229 module_exit(ttyprintk_exit);
 230
 231 MODULE_DESCRIPTION("TTY driver to output user messages via printk");
 232 MODULE_LICENSE("GPL");