watchdog_dev.c

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/*
 *  watchdog_dev.c
 *
 *  (c) Copyright 2008-2011 Alan Cox <[email protected]>,
 *                      All Rights Reserved.
 *
 *  (c) Copyright 2008-2011 Wim Van Sebroeck <[email protected]>.
 *
 *
 *  This source code is part of the generic code that can be used
 *  by all the watchdog timer drivers.
 *
 *  This part of the generic code takes care of the following
 *  misc device: /dev/watchdog.
 *
 *  Based on source code of the following authors:
 *    Matt Domsch <[email protected]>,
 *    Rob Radez <[email protected]>,
 *    Rusty Lynch <[email protected]>
 *    Satyam Sharma <[email protected]>
 *    Randy Dunlap <[email protected]>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 *
 *  Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
 *  admit liability nor provide warranty for any of this software.
 *  This material is provided "AS-IS" and at no charge.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>   /* For module stuff/... */
#include <linux/types.h>    /* For standard types (like size_t) */
#include <linux/errno.h>    /* For the -ENODEV/... values */
#include <linux/kernel.h>   /* For printk/panic/... */
#include <linux/fs.h>       /* For file operations */
#include <linux/watchdog.h> /* For watchdog specific items */
#include <linux/miscdevice.h>   /* For handling misc devices */
#include <linux/init.h>     /* For __init/__exit/... */
#include <linux/uaccess.h>  /* For copy_to_user/put_user/... */

#include "watchdog_core.h"

/* the dev_t structure to store the dynamically allocated watchdog devices */
static dev_t watchdog_devt;
/* the watchdog device behind /dev/watchdog */
static struct watchdog_device *old_wdd;

/*
 *  watchdog_ping: ping the watchdog.
 *  @wddev: the watchdog device to ping
 *
 *  If the watchdog has no own ping operation then it needs to be
 *  restarted via the start operation. This wrapper function does
 *  exactly that.
 *  We only ping when the watchdog device is running.
 */

static int watchdog_ping(struct watchdog_device *wddev)
{
    int err = 0;

    mutex_lock(&wddev->lock);

    if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
        err = -ENODEV;
        goto out_ping;
    }

    if (!watchdog_active(wddev))
        goto out_ping;

    if (wddev->ops->ping)
        err = wddev->ops->ping(wddev);  /* ping the watchdog */
    else
        err = wddev->ops->start(wddev); /* restart watchdog */

out_ping:
    mutex_unlock(&wddev->lock);
    return err;
}

/*
 *  watchdog_start: wrapper to start the watchdog.
 *  @wddev: the watchdog device to start
 *
 *  Start the watchdog if it is not active and mark it active.
 *  This function returns zero on success or a negative errno code for
 *  failure.
 */

static int watchdog_start(struct watchdog_device *wddev)
{
    int err = 0;

    mutex_lock(&wddev->lock);

    if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
        err = -ENODEV;
        goto out_start;
    }

    if (watchdog_active(wddev))
        goto out_start;

    err = wddev->ops->start(wddev);
    if (err == 0)
        set_bit(WDOG_ACTIVE, &wddev->status);

out_start:
    mutex_unlock(&wddev->lock);
    return err;
}

/*
 *  watchdog_stop: wrapper to stop the watchdog.
 *  @wddev: the watchdog device to stop
 *
 *  Stop the watchdog if it is still active and unmark it active.
 *  This function returns zero on success or a negative errno code for
 *  failure.
 *  If the 'nowayout' feature was set, the watchdog cannot be stopped.
 */

static int watchdog_stop(struct watchdog_device *wddev)
{
    int err = 0;

    mutex_lock(&wddev->lock);

    if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
        err = -ENODEV;
        goto out_stop;
    }

    if (!watchdog_active(wddev))
        goto out_stop;

    if (test_bit(WDOG_NO_WAY_OUT, &wddev->status)) {
        dev_info(wddev->dev, "nowayout prevents watchdog being stopped!\n");
        err = -EBUSY;
        goto out_stop;
    }

    err = wddev->ops->stop(wddev);
    if (err == 0)
        clear_bit(WDOG_ACTIVE, &wddev->status);

out_stop:
    mutex_unlock(&wddev->lock);
    return err;
}

/*
 *  watchdog_get_status: wrapper to get the watchdog status
 *  @wddev: the watchdog device to get the status from
 *  @status: the status of the watchdog device
 *
 *  Get the watchdog's status flags.
 */

static int watchdog_get_status(struct watchdog_device *wddev,
                            unsigned int *status)
{
    int err = 0;

    *status = 0;
    if (!wddev->ops->status)
        return -EOPNOTSUPP;

    mutex_lock(&wddev->lock);

    if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
        err = -ENODEV;
        goto out_status;
    }

    *status = wddev->ops->status(wddev);

out_status:
    mutex_unlock(&wddev->lock);
    return err;
}

/*
 *  watchdog_set_timeout: set the watchdog timer timeout
 *  @wddev: the watchdog device to set the timeout for
 *  @timeout: timeout to set in seconds
 */

static int watchdog_set_timeout(struct watchdog_device *wddev,
                            unsigned int timeout)
{
    int err;

    if ((wddev->ops->set_timeout == NULL) ||
        !(wddev->info->options & WDIOF_SETTIMEOUT))
        return -EOPNOTSUPP;

    if ((wddev->max_timeout != 0) &&
        (timeout < wddev->min_timeout || timeout > wddev->max_timeout))
        return -EINVAL;

    mutex_lock(&wddev->lock);

    if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
        err = -ENODEV;
        goto out_timeout;
    }

    err = wddev->ops->set_timeout(wddev, timeout);

out_timeout:
    mutex_unlock(&wddev->lock);
    return err;
}

/*
 *  watchdog_get_timeleft: wrapper to get the time left before a reboot
 *  @wddev: the watchdog device to get the remaining time from
 *  @timeleft: the time that's left
 *
 *  Get the time before a watchdog will reboot (if not pinged).
 */

static int watchdog_get_timeleft(struct watchdog_device *wddev,
                            unsigned int *timeleft)
{
    int err = 0;

    *timeleft = 0;
    if (!wddev->ops->get_timeleft)
        return -EOPNOTSUPP;

    mutex_lock(&wddev->lock);

    if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
        err = -ENODEV;
        goto out_timeleft;
    }

    *timeleft = wddev->ops->get_timeleft(wddev);

out_timeleft:
    mutex_unlock(&wddev->lock);
    return err;
}

/*
 *  watchdog_ioctl_op: call the watchdog drivers ioctl op if defined
 *  @wddev: the watchdog device to do the ioctl on
 *  @cmd: watchdog command
 *  @arg: argument pointer
 */

static int watchdog_ioctl_op(struct watchdog_device *wddev, unsigned int cmd,
                            unsigned long arg)
{
    int err;

    if (!wddev->ops->ioctl)
        return -ENOIOCTLCMD;

    mutex_lock(&wddev->lock);

    if (test_bit(WDOG_UNREGISTERED, &wddev->status)) {
        err = -ENODEV;
        goto out_ioctl;
    }

    err = wddev->ops->ioctl(wddev, cmd, arg);

out_ioctl:
    mutex_unlock(&wddev->lock);
    return err;
}

/*
 *  watchdog_write: writes to the watchdog.
 *  @file: file from VFS
 *  @data: user address of data
 *  @len: length of data
 *  @ppos: pointer to the file offset
 *
 *  A write to a watchdog device is defined as a keepalive ping.
 *  Writing the magic 'V' sequence allows the next close to turn
 *  off the watchdog (if 'nowayout' is not set).
 */

static ssize_t watchdog_write(struct file *file, const char __user *data,
                        size_t len, loff_t *ppos)
{
    struct watchdog_device *wdd = file->private_data;
    size_t i;
    char c;

    if (len == 0)
        return 0;

    /*
     * Note: just in case someone wrote the magic character
     * five months ago...
     */
    clear_bit(WDOG_ALLOW_RELEASE, &wdd->status);

    /* scan to see whether or not we got the magic character */
    for (i = 0; i != len; i++) {
        if (get_user(c, data + i))
            return -EFAULT;
        if (c == 'V')
            set_bit(WDOG_ALLOW_RELEASE, &wdd->status);
    }

    /* someone wrote to us, so we send the watchdog a keepalive ping */
    watchdog_ping(wdd);

    return len;
}

/*
 *  watchdog_ioctl: handle the different ioctl's for the watchdog device.
 *  @file: file handle to the device
 *  @cmd: watchdog command
 *  @arg: argument pointer
 *
 *  The watchdog API defines a common set of functions for all watchdogs
 *  according to their available features.
 */

static long watchdog_ioctl(struct file *file, unsigned int cmd,
                            unsigned long arg)
{
    struct watchdog_device *wdd = file->private_data;
    void __user *argp = (void __user *)arg;
    int __user *p = argp;
    unsigned int val;
    int err;

    err = watchdog_ioctl_op(wdd, cmd, arg);
    if (err != -ENOIOCTLCMD)
        return err;

    switch (cmd) {
    case WDIOC_GETSUPPORT:
        return copy_to_user(argp, wdd->info,
            sizeof(struct watchdog_info)) ? -EFAULT : 0;
    case WDIOC_GETSTATUS:
        err = watchdog_get_status(wdd, &val);
        if (err == -ENODEV)
            return err;
        return put_user(val, p);
    case WDIOC_GETBOOTSTATUS:
        return put_user(wdd->bootstatus, p);
    case WDIOC_SETOPTIONS:
        if (get_user(val, p))
            return -EFAULT;
        if (val & WDIOS_DISABLECARD) {
            err = watchdog_stop(wdd);
            if (err < 0)
                return err;
        }
        if (val & WDIOS_ENABLECARD) {
            err = watchdog_start(wdd);
            if (err < 0)
                return err;
        }
        return 0;
    case WDIOC_KEEPALIVE:
        if (!(wdd->info->options & WDIOF_KEEPALIVEPING))
            return -EOPNOTSUPP;
        watchdog_ping(wdd);
        return 0;
    case WDIOC_SETTIMEOUT:
        if (get_user(val, p))
            return -EFAULT;
        err = watchdog_set_timeout(wdd, val);
        if (err < 0)
            return err;
        /* If the watchdog is active then we send a keepalive ping
         * to make sure that the watchdog keep's running (and if
         * possible that it takes the new timeout) */
        watchdog_ping(wdd);
        /* Fall */
    case WDIOC_GETTIMEOUT:
        /* timeout == 0 means that we don't know the timeout */
        if (wdd->timeout == 0)
            return -EOPNOTSUPP;
        return put_user(wdd->timeout, p);
    case WDIOC_GETTIMELEFT:
        err = watchdog_get_timeleft(wdd, &val);
        if (err)
            return err;
        return put_user(val, p);
    default:
        return -ENOTTY;
    }
}

/*
 *  watchdog_open: open the /dev/watchdog* devices.
 *  @inode: inode of device
 *  @file: file handle to device
 *
 *  When the /dev/watchdog* device gets opened, we start the watchdog.
 *  Watch out: the /dev/watchdog device is single open, so we make sure
 *  it can only be opened once.
 */

static int watchdog_open(struct inode *inode, struct file *file)
{
    int err = -EBUSY;
    struct watchdog_device *wdd;

    /* Get the corresponding watchdog device */
    if (imajor(inode) == MISC_MAJOR)
        wdd = old_wdd;
    else
        wdd = container_of(inode->i_cdev, struct watchdog_device, cdev);

    /* the watchdog is single open! */
    if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status))
        return -EBUSY;

    /*
     * If the /dev/watchdog device is open, we don't want the module
     * to be unloaded.
     */
    if (!try_module_get(wdd->ops->owner))
        goto out;

    err = watchdog_start(wdd);
    if (err < 0)
        goto out_mod;

    file->private_data = wdd;

    if (wdd->ops->ref)
        wdd->ops->ref(wdd);

    /* dev/watchdog is a virtual (and thus non-seekable) filesystem */
    return nonseekable_open(inode, file);

out_mod:
    module_put(wdd->ops->owner);
out:
    clear_bit(WDOG_DEV_OPEN, &wdd->status);
    return err;
}

/*
 *  watchdog_release: release the watchdog device.
 *  @inode: inode of device
 *  @file: file handle to device
 *
 *  This is the code for when /dev/watchdog gets closed. We will only
 *  stop the watchdog when we have received the magic char (and nowayout
 *  was not set), else the watchdog will keep running.
 */

static int watchdog_release(struct inode *inode, struct file *file)
{
    struct watchdog_device *wdd = file->private_data;
    int err = -EBUSY;

    /*
     * We only stop the watchdog if we received the magic character
     * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then
     * watchdog_stop will fail.
     */
    if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) ||
        !(wdd->info->options & WDIOF_MAGICCLOSE))
        err = watchdog_stop(wdd);

    /* If the watchdog was not stopped, send a keepalive ping */
    if (err < 0) {
        mutex_lock(&wdd->lock);
        if (!test_bit(WDOG_UNREGISTERED, &wdd->status))
            dev_crit(wdd->dev, "watchdog did not stop!\n");
        mutex_unlock(&wdd->lock);
        watchdog_ping(wdd);
    }

    /* Allow the owner module to be unloaded again */
    module_put(wdd->ops->owner);

    /* make sure that /dev/watchdog can be re-opened */
    clear_bit(WDOG_DEV_OPEN, &wdd->status);

    /* Note wdd may be gone after this, do not use after this! */
    if (wdd->ops->unref)
        wdd->ops->unref(wdd);

    return 0;
}

static const struct file_operations watchdog_fops = {
    .owner      = THIS_MODULE,
    .write      = watchdog_write,
    .unlocked_ioctl = watchdog_ioctl,
    .open       = watchdog_open,
    .release    = watchdog_release,
};

static struct miscdevice watchdog_miscdev = {
    .minor      = WATCHDOG_MINOR,
    .name       = "watchdog",
    .fops       = &watchdog_fops,
};

/*
 *  watchdog_dev_register: register a watchdog device
 *  @watchdog: watchdog device
 *
 *  Register a watchdog device including handling the legacy
 *  /dev/watchdog node. /dev/watchdog is actually a miscdevice and
 *  thus we set it up like that.
 */

int watchdog_dev_register(struct watchdog_device *watchdog)
{
    int err, devno;

    if (watchdog->id == 0) {
        watchdog_miscdev.parent = watchdog->parent;
        err = misc_register(&watchdog_miscdev);
        if (err != 0) {
            pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
                watchdog->info->identity, WATCHDOG_MINOR, err);
            if (err == -EBUSY)
                pr_err("%s: a legacy watchdog module is probably present.\n",
                    watchdog->info->identity);
            return err;
        }
        old_wdd = watchdog;
    }

    /* Fill in the data structures */
    devno = MKDEV(MAJOR(watchdog_devt), watchdog->id);
    cdev_init(&watchdog->cdev, &watchdog_fops);
    watchdog->cdev.owner = watchdog->ops->owner;

    /* Add the device */
    err  = cdev_add(&watchdog->cdev, devno, 1);
    if (err) {
        pr_err("watchdog%d unable to add device %d:%d\n",
            watchdog->id,  MAJOR(watchdog_devt), watchdog->id);
        if (watchdog->id == 0) {
            misc_deregister(&watchdog_miscdev);
            old_wdd = NULL;
        }
    }
    return err;
}

/*
 *  watchdog_dev_unregister: unregister a watchdog device
 *  @watchdog: watchdog device
 *
 *  Unregister the watchdog and if needed the legacy /dev/watchdog device.
 */

int watchdog_dev_unregister(struct watchdog_device *watchdog)
{
    mutex_lock(&watchdog->lock);
    set_bit(WDOG_UNREGISTERED, &watchdog->status);
    mutex_unlock(&watchdog->lock);

    cdev_del(&watchdog->cdev);
    if (watchdog->id == 0) {
        misc_deregister(&watchdog_miscdev);
        old_wdd = NULL;
    }
    return 0;
}

/*
 *  watchdog_dev_init: init dev part of watchdog core
 *
 *  Allocate a range of chardev nodes to use for watchdog devices
 */

int __init watchdog_dev_init(void)
{
    int err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
    if (err < 0)
        pr_err("watchdog: unable to allocate char dev region\n");
    return err;
}

/*
 *  watchdog_dev_exit: exit dev part of watchdog core
 *
 *  Release the range of chardev nodes used for watchdog devices
 */

void __exit watchdog_dev_exit(void)
{
    unregister_chrdev_region(watchdog_devt, MAX_DOGS);
}