drivers/char/ttyprintk.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  *  linux/drivers/char/ttyprintk.c
0004  *
0005  *  Copyright (C) 2010  Samo Pogacnik
0006  */
0007
0008 /*
0009  * This pseudo device allows user to make printk messages. It is possible
0010  * to store "console" messages inline with kernel messages for better analyses
0011  * of the boot process, for example.
0012  */
0013
0014 #include <linux/console.h>
0015 #include <linux/device.h>
0016 #include <linux/serial.h>
0017 #include <linux/tty.h>
0018 #include <linux/module.h>
0019 #include <linux/spinlock.h>
0020
0021 struct ttyprintk_port {
0022     struct tty_port port;
0023     spinlock_t spinlock;
0024 };
0025
0026 static struct ttyprintk_port tpk_port;
0027
0028 /*
0029  * Our simple preformatting supports transparent output of (time-stamped)
0030  * printk messages (also suitable for logging service):
0031  * - any cr is replaced by nl
0032  * - adds a ttyprintk source tag in front of each line
0033  * - too long message is fragmented, with '\'nl between fragments
0034  * - TPK_STR_SIZE isn't really the write_room limiting factor, because
0035  *   it is emptied on the fly during preformatting.
0036  */
0037 #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
0038 #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
0039 #define TPK_PREFIX KERN_SOH __stringify(CONFIG_TTY_PRINTK_LEVEL)
0040
0041 static int tpk_curr;
0042
0043 static char tpk_buffer[TPK_STR_SIZE + 4];
0044
0045 static void tpk_flush(void)
0046 {
0047     if (tpk_curr > 0) {
0048         tpk_buffer[tpk_curr] = '\0';
0049         printk(TPK_PREFIX "[U] %s\n", tpk_buffer);
0050         tpk_curr = 0;
0051     }
0052 }
0053
0054 static int tpk_printk(const unsigned char *buf, int count)
0055 {
0056     int i;
0057
0058     for (i = 0; i < count; i++) {
0059         if (tpk_curr >= TPK_STR_SIZE) {
0060             /* end of tmp buffer reached: cut the message in two */
0061             tpk_buffer[tpk_curr++] = '\\';
0062             tpk_flush();
0063         }
0064
0065         switch (buf[i]) {
0066         case '\r':
0067             tpk_flush();
0068             if ((i + 1) < count && buf[i + 1] == '\n')
0069                 i++;
0070             break;
0071         case '\n':
0072             tpk_flush();
0073             break;
0074         default:
0075             tpk_buffer[tpk_curr++] = buf[i];
0076             break;
0077         }
0078     }
0079
0080     return count;
0081 }
0082
0083 /*
0084  * TTY operations open function.
0085  */
0086 static int tpk_open(struct tty_struct *tty, struct file *filp)
0087 {
0088     tty->driver_data = &tpk_port;
0089
0090     return tty_port_open(&tpk_port.port, tty, filp);
0091 }
0092
0093 /*
0094  * TTY operations close function.
0095  */
0096 static void tpk_close(struct tty_struct *tty, struct file *filp)
0097 {
0098     struct ttyprintk_port *tpkp = tty->driver_data;
0099
0100     tty_port_close(&tpkp->port, tty, filp);
0101 }
0102
0103 /*
0104  * TTY operations write function.
0105  */
0106 static int tpk_write(struct tty_struct *tty,
0107         const unsigned char *buf, int count)
0108 {
0109     struct ttyprintk_port *tpkp = tty->driver_data;
0110     unsigned long flags;
0111     int ret;
0112
0113     /* exclusive use of tpk_printk within this tty */
0114     spin_lock_irqsave(&tpkp->spinlock, flags);
0115     ret = tpk_printk(buf, count);
0116     spin_unlock_irqrestore(&tpkp->spinlock, flags);
0117
0118     return ret;
0119 }
0120
0121 /*
0122  * TTY operations write_room function.
0123  */
0124 static unsigned int tpk_write_room(struct tty_struct *tty)
0125 {
0126     return TPK_MAX_ROOM;
0127 }
0128
0129 /*
0130  * TTY operations hangup function.
0131  */
0132 static void tpk_hangup(struct tty_struct *tty)
0133 {
0134     struct ttyprintk_port *tpkp = tty->driver_data;
0135
0136     tty_port_hangup(&tpkp->port);
0137 }
0138
0139 /*
0140  * TTY port operations shutdown function.
0141  */
0142 static void tpk_port_shutdown(struct tty_port *tport)
0143 {
0144     struct ttyprintk_port *tpkp =
0145         container_of(tport, struct ttyprintk_port, port);
0146     unsigned long flags;
0147
0148     spin_lock_irqsave(&tpkp->spinlock, flags);
0149     tpk_flush();
0150     spin_unlock_irqrestore(&tpkp->spinlock, flags);
0151 }
0152
0153 static const struct tty_operations ttyprintk_ops = {
0154     .open = tpk_open,
0155     .close = tpk_close,
0156     .write = tpk_write,
0157     .write_room = tpk_write_room,
0158     .hangup = tpk_hangup,
0159 };
0160
0161 static const struct tty_port_operations tpk_port_ops = {
0162     .shutdown = tpk_port_shutdown,
0163 };
0164
0165 static struct tty_driver *ttyprintk_driver;
0166
0167 static struct tty_driver *ttyprintk_console_device(struct console *c,
0168                            int *index)
0169 {
0170     *index = 0;
0171     return ttyprintk_driver;
0172 }
0173
0174 static struct console ttyprintk_console = {
0175     .name = "ttyprintk",
0176     .device = ttyprintk_console_device,
0177 };
0178
0179 static int __init ttyprintk_init(void)
0180 {
0181     int ret;
0182
0183     spin_lock_init(&tpk_port.spinlock);
0184
0185     ttyprintk_driver = tty_alloc_driver(1,
0186             TTY_DRIVER_RESET_TERMIOS |
0187             TTY_DRIVER_REAL_RAW |
0188             TTY_DRIVER_UNNUMBERED_NODE);
0189     if (IS_ERR(ttyprintk_driver))
0190         return PTR_ERR(ttyprintk_driver);
0191
0192     tty_port_init(&tpk_port.port);
0193     tpk_port.port.ops = &tpk_port_ops;
0194
0195     ttyprintk_driver->driver_name = "ttyprintk";
0196     ttyprintk_driver->name = "ttyprintk";
0197     ttyprintk_driver->major = TTYAUX_MAJOR;
0198     ttyprintk_driver->minor_start = 3;
0199     ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
0200     ttyprintk_driver->init_termios = tty_std_termios;
0201     ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
0202     tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
0203     tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);
0204
0205     ret = tty_register_driver(ttyprintk_driver);
0206     if (ret < 0) {
0207         printk(KERN_ERR "Couldn't register ttyprintk driver\n");
0208         goto error;
0209     }
0210
0211     register_console(&ttyprintk_console);
0212
0213     return 0;
0214
0215 error:
0216     tty_driver_kref_put(ttyprintk_driver);
0217     tty_port_destroy(&tpk_port.port);
0218     return ret;
0219 }
0220
0221 static void __exit ttyprintk_exit(void)
0222 {
0223     unregister_console(&ttyprintk_console);
0224     tty_unregister_driver(ttyprintk_driver);
0225     tty_driver_kref_put(ttyprintk_driver);
0226     tty_port_destroy(&tpk_port.port);
0227 }
0228
0229 device_initcall(ttyprintk_init);
0230 module_exit(ttyprintk_exit);
0231
0232 MODULE_LICENSE("GPL");