ttyprintk.c

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/*
 *  linux/drivers/char/ttyprintk.c
 *
 *  Copyright (C) 2010  Samo Pogacnik
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the smems of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 */

/*
 * This pseudo device allows user to make printk messages. It is possible
 * to store "console" messages inline with kernel messages for better analyses
 * of the boot process, for example.
 */

#include <linux/device.h>
#include <linux/serial.h>
#include <linux/tty.h>
#include <linux/export.h>

struct ttyprintk_port {
    struct tty_port port;
    struct mutex port_write_mutex;
};

static struct ttyprintk_port tpk_port;

/*
 * Our simple preformatting supports transparent output of (time-stamped)
 * printk messages (also suitable for logging service):
 * - any cr is replaced by nl
 * - adds a ttyprintk source tag in front of each line
 * - too long message is fragmeted, with '\'nl between fragments
 * - TPK_STR_SIZE isn't really the write_room limiting factor, bcause
 *   it is emptied on the fly during preformatting.
 */
#define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
#define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
static const char *tpk_tag = "[U] "; /* U for User */
static int tpk_curr;

static int tpk_printk(const unsigned char *buf, int count)
{
    static char tmp[TPK_STR_SIZE + 4];
    int i = tpk_curr;

    if (buf == NULL) {
        /* flush tmp[] */
        if (tpk_curr > 0) {
            /* non nl or cr terminated message - add nl */
            tmp[tpk_curr + 0] = '\n';
            tmp[tpk_curr + 1] = '\0';
            printk(KERN_INFO "%s%s", tpk_tag, tmp);
            tpk_curr = 0;
        }
        return i;
    }

    for (i = 0; i < count; i++) {
        tmp[tpk_curr] = buf[i];
        if (tpk_curr < TPK_STR_SIZE) {
            switch (buf[i]) {
            case '\r':
                /* replace cr with nl */
                tmp[tpk_curr + 0] = '\n';
                tmp[tpk_curr + 1] = '\0';
                printk(KERN_INFO "%s%s", tpk_tag, tmp);
                tpk_curr = 0;
                if ((i + 1) < count && buf[i + 1] == '\n')
                    i++;
                break;
            case '\n':
                tmp[tpk_curr + 1] = '\0';
                printk(KERN_INFO "%s%s", tpk_tag, tmp);
                tpk_curr = 0;
                break;
            default:
                tpk_curr++;
            }
        } else {
            /* end of tmp buffer reached: cut the message in two */
            tmp[tpk_curr + 1] = '\\';
            tmp[tpk_curr + 2] = '\n';
            tmp[tpk_curr + 3] = '\0';
            printk(KERN_INFO "%s%s", tpk_tag, tmp);
            tpk_curr = 0;
        }
    }

    return count;
}

/*
 * TTY operations open function.
 */
static int tpk_open(struct tty_struct *tty, struct file *filp)
{
    tty->driver_data = &tpk_port;

    return tty_port_open(&tpk_port.port, tty, filp);
}

/*
 * TTY operations close function.
 */
static void tpk_close(struct tty_struct *tty, struct file *filp)
{
    struct ttyprintk_port *tpkp = tty->driver_data;

    mutex_lock(&tpkp->port_write_mutex);
    /* flush tpk_printk buffer */
    tpk_printk(NULL, 0);
    mutex_unlock(&tpkp->port_write_mutex);

    tty_port_close(&tpkp->port, tty, filp);
}

/*
 * TTY operations write function.
 */
static int tpk_write(struct tty_struct *tty,
        const unsigned char *buf, int count)
{
    struct ttyprintk_port *tpkp = tty->driver_data;
    int ret;


    /* exclusive use of tpk_printk within this tty */
    mutex_lock(&tpkp->port_write_mutex);
    ret = tpk_printk(buf, count);
    mutex_unlock(&tpkp->port_write_mutex);

    return ret;
}

/*
 * TTY operations write_room function.
 */
static int tpk_write_room(struct tty_struct *tty)
{
    return TPK_MAX_ROOM;
}

/*
 * TTY operations ioctl function.
 */
static int tpk_ioctl(struct tty_struct *tty,
            unsigned int cmd, unsigned long arg)
{
    struct ttyprintk_port *tpkp = tty->driver_data;

    if (!tpkp)
        return -EINVAL;

    switch (cmd) {
    /* Stop TIOCCONS */
    case TIOCCONS:
        return -EOPNOTSUPP;
    default:
        return -ENOIOCTLCMD;
    }
    return 0;
}

static const struct tty_operations ttyprintk_ops = {
    .open = tpk_open,
    .close = tpk_close,
    .write = tpk_write,
    .write_room = tpk_write_room,
    .ioctl = tpk_ioctl,
};

static struct tty_port_operations null_ops = { };

static struct tty_driver *ttyprintk_driver;

static int __init ttyprintk_init(void)
{
    int ret = -ENOMEM;

    tty_port_init(&tpk_port.port);
    tpk_port.port.ops = &null_ops;
    mutex_init(&tpk_port.port_write_mutex);

    ttyprintk_driver = tty_alloc_driver(1,
            TTY_DRIVER_RESET_TERMIOS |
            TTY_DRIVER_REAL_RAW |
            TTY_DRIVER_UNNUMBERED_NODE);
    if (IS_ERR(ttyprintk_driver))
        return PTR_ERR(ttyprintk_driver);

    ttyprintk_driver->driver_name = "ttyprintk";
    ttyprintk_driver->name = "ttyprintk";
    ttyprintk_driver->major = TTYAUX_MAJOR;
    ttyprintk_driver->minor_start = 3;
    ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
    ttyprintk_driver->init_termios = tty_std_termios;
    ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
    tty_set_operations(ttyprintk_driver, &ttyprintk_ops);
    tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);

    ret = tty_register_driver(ttyprintk_driver);
    if (ret < 0) {
        printk(KERN_ERR "Couldn't register ttyprintk driver\n");
        goto error;
    }

    return 0;

error:
    tty_unregister_driver(ttyprintk_driver);
    put_tty_driver(ttyprintk_driver);
    ttyprintk_driver = NULL;
    return ret;
}
module_init(ttyprintk_init);