[mirror_ubuntu-bionic-kernel.git] / drivers / watchdog / watchdog_dev.c

/*
 *      watchdog_dev.c
 *
 *      (c) Copyright 2008-2011 Alan Cox <alan@lxorguk.ukuu.org.uk>,
 *                                              All Rights Reserved.
 *
 *      (c) Copyright 2008-2011 Wim Van Sebroeck <wim@iguana.be>.
 *
 *
 *      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 <Matt_Domsch@dell.com>,
 *        Rob Radez <rob@osinvestor.com>,
 *        Rusty Lynch <rusty@linux.co.intel.com>
 *        Satyam Sharma <satyam@infradead.org>
 *        Randy Dunlap <randy.dunlap@oracle.com>
 *
 *      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/cdev.h>         /* For character device */
#include <linux/errno.h>        /* For the -ENODEV/... values */
#include <linux/fs.h>           /* For file operations */
#include <linux/init.h>         /* For __init/__exit/... */
#include <linux/jiffies.h>      /* For timeout functions */
#include <linux/kernel.h>       /* For printk/panic/... */
#include <linux/kref.h>         /* For data references */
#include <linux/miscdevice.h>   /* For handling misc devices */
#include <linux/module.h>       /* For module stuff/... */
#include <linux/mutex.h>        /* For mutexes */
#include <linux/slab.h>         /* For memory functions */
#include <linux/types.h>        /* For standard types (like size_t) */
#include <linux/watchdog.h>     /* For watchdog specific items */
#include <linux/workqueue.h>    /* For workqueue */
#include <linux/uaccess.h>      /* For copy_to_user/put_user/... */

#include "watchdog_core.h"
#include "watchdog_pretimeout.h"

/*
 * struct watchdog_core_data - watchdog core internal data
 * @kref:       Reference count.
 * @cdev:       The watchdog's Character device.
 * @wdd:        Pointer to watchdog device.
 * @lock:       Lock for watchdog core.
 * @status:     Watchdog core internal status bits.
 */
struct watchdog_core_data {
        struct kref kref;
        struct cdev cdev;
        struct watchdog_device *wdd;
        struct mutex lock;
        unsigned long last_keepalive;
        unsigned long last_hw_keepalive;
        struct delayed_work work;
        unsigned long status;           /* Internal status bits */
#define _WDOG_DEV_OPEN          0       /* Opened ? */
#define _WDOG_ALLOW_RELEASE     1       /* Did we receive the magic char ? */
#define _WDOG_KEEPALIVE         2       /* Did we receive a keepalive ? */
};

/* the dev_t structure to store the dynamically allocated watchdog devices */
static dev_t watchdog_devt;
/* Reference to watchdog device behind /dev/watchdog */
static struct watchdog_core_data *old_wd_data;

static struct workqueue_struct *watchdog_wq;

static bool handle_boot_enabled =
        IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED);

static inline bool watchdog_need_worker(struct watchdog_device *wdd)
{
        /* All variables in milli-seconds */
        unsigned int hm = wdd->max_hw_heartbeat_ms;
        unsigned int t = wdd->timeout * 1000;

        /*
         * A worker to generate heartbeat requests is needed if all of the
         * following conditions are true.
         * - Userspace activated the watchdog.
         * - The driver provided a value for the maximum hardware timeout, and
         *   thus is aware that the framework supports generating heartbeat
         *   requests.
         * - Userspace requests a longer timeout than the hardware can handle.
         *
         * Alternatively, if userspace has not opened the watchdog
         * device, we take care of feeding the watchdog if it is
         * running.
         */
        return (hm && watchdog_active(wdd) && t > hm) ||
                (t && !watchdog_active(wdd) && watchdog_hw_running(wdd));
}

static long watchdog_next_keepalive(struct watchdog_device *wdd)
{
        struct watchdog_core_data *wd_data = wdd->wd_data;
        unsigned int timeout_ms = wdd->timeout * 1000;
        unsigned long keepalive_interval;
        unsigned long last_heartbeat;
        unsigned long virt_timeout;
        unsigned int hw_heartbeat_ms;

        virt_timeout = wd_data->last_keepalive + msecs_to_jiffies(timeout_ms);
        hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
        keepalive_interval = msecs_to_jiffies(hw_heartbeat_ms / 2);

        if (!watchdog_active(wdd))
                return keepalive_interval;

        /*
         * To ensure that the watchdog times out wdd->timeout seconds
         * after the most recent ping from userspace, the last
         * worker ping has to come in hw_heartbeat_ms before this timeout.
         */
        last_heartbeat = virt_timeout - msecs_to_jiffies(hw_heartbeat_ms);
        return min_t(long, last_heartbeat - jiffies, keepalive_interval);
}

static inline void watchdog_update_worker(struct watchdog_device *wdd)
{
        struct watchdog_core_data *wd_data = wdd->wd_data;

        if (watchdog_need_worker(wdd)) {
                long t = watchdog_next_keepalive(wdd);

                if (t > 0)
                        mod_delayed_work(watchdog_wq, &wd_data->work, t);
        } else {
                cancel_delayed_work(&wd_data->work);
        }
}

static int __watchdog_ping(struct watchdog_device *wdd)
{
        struct watchdog_core_data *wd_data = wdd->wd_data;
        unsigned long earliest_keepalive = wd_data->last_hw_keepalive +
                                msecs_to_jiffies(wdd->min_hw_heartbeat_ms);
        int err;

        if (time_is_after_jiffies(earliest_keepalive)) {
                mod_delayed_work(watchdog_wq, &wd_data->work,
                                 earliest_keepalive - jiffies);
                return 0;
        }

        wd_data->last_hw_keepalive = jiffies;

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

        watchdog_update_worker(wdd);

        return err;
}

/*
 *      watchdog_ping: ping the watchdog.
 *      @wdd: the watchdog device to ping
 *
 *      The caller must hold wd_data->lock.
 *
 *      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 *wdd)
{
        struct watchdog_core_data *wd_data = wdd->wd_data;

        if (!watchdog_active(wdd) && !watchdog_hw_running(wdd))
                return 0;

        set_bit(_WDOG_KEEPALIVE, &wd_data->status);

        wd_data->last_keepalive = jiffies;
        return __watchdog_ping(wdd);
}

static void watchdog_ping_work(struct work_struct *work)
{
        struct watchdog_core_data *wd_data;
        struct watchdog_device *wdd;

        wd_data = container_of(to_delayed_work(work), struct watchdog_core_data,
                               work);

        mutex_lock(&wd_data->lock);
        wdd = wd_data->wdd;
        if (wdd && (watchdog_active(wdd) || watchdog_hw_running(wdd)))
                __watchdog_ping(wdd);
        mutex_unlock(&wd_data->lock);
}

/*
 *      watchdog_start: wrapper to start the watchdog.
 *      @wdd: the watchdog device to start
 *
 *      The caller must hold wd_data->lock.
 *
 *      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 *wdd)
{
        struct watchdog_core_data *wd_data = wdd->wd_data;
        unsigned long started_at;
        int err;

        if (watchdog_active(wdd))
                return 0;

        set_bit(_WDOG_KEEPALIVE, &wd_data->status);

        started_at = jiffies;
        if (watchdog_hw_running(wdd) && wdd->ops->ping)
                err = wdd->ops->ping(wdd);
        else
                err = wdd->ops->start(wdd);
        if (err == 0) {
                set_bit(WDOG_ACTIVE, &wdd->status);
                wd_data->last_keepalive = started_at;
                watchdog_update_worker(wdd);
        }

        return err;
}

/*
 *      watchdog_stop: wrapper to stop the watchdog.
 *      @wdd: the watchdog device to stop
 *
 *      The caller must hold wd_data->lock.
 *
 *      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 *wdd)
{
        int err = 0;

        if (!watchdog_active(wdd))
                return 0;

        if (test_bit(WDOG_NO_WAY_OUT, &wdd->status)) {
                pr_info("watchdog%d: nowayout prevents watchdog being stopped!\n",
                        wdd->id);
                return -EBUSY;
        }

        if (wdd->ops->stop) {
                clear_bit(WDOG_HW_RUNNING, &wdd->status);
                err = wdd->ops->stop(wdd);
        } else {
                set_bit(WDOG_HW_RUNNING, &wdd->status);
        }

        if (err == 0) {
                clear_bit(WDOG_ACTIVE, &wdd->status);
                watchdog_update_worker(wdd);
        }

        return err;
}

/*
 *      watchdog_get_status: wrapper to get the watchdog status
 *      @wdd: the watchdog device to get the status from
 *
 *      The caller must hold wd_data->lock.
 *
 *      Get the watchdog's status flags.
 */

static unsigned int watchdog_get_status(struct watchdog_device *wdd)
{
        struct watchdog_core_data *wd_data = wdd->wd_data;
        unsigned int status;

        if (wdd->ops->status)
                status = wdd->ops->status(wdd);
        else
                status = wdd->bootstatus & (WDIOF_CARDRESET |
                                            WDIOF_OVERHEAT |
                                            WDIOF_FANFAULT |
                                            WDIOF_EXTERN1 |
                                            WDIOF_EXTERN2 |
                                            WDIOF_POWERUNDER |
                                            WDIOF_POWEROVER);

        if (test_bit(_WDOG_ALLOW_RELEASE, &wd_data->status))
                status |= WDIOF_MAGICCLOSE;

        if (test_and_clear_bit(_WDOG_KEEPALIVE, &wd_data->status))
                status |= WDIOF_KEEPALIVEPING;

        return status;
}

/*
 *      watchdog_set_timeout: set the watchdog timer timeout
 *      @wdd: the watchdog device to set the timeout for
 *      @timeout: timeout to set in seconds
 *
 *      The caller must hold wd_data->lock.
 */

static int watchdog_set_timeout(struct watchdog_device *wdd,
                                                        unsigned int timeout)
{
        int err = 0;

        if (!(wdd->info->options & WDIOF_SETTIMEOUT))
                return -EOPNOTSUPP;

        if (watchdog_timeout_invalid(wdd, timeout))
                return -EINVAL;

        if (wdd->ops->set_timeout) {
                err = wdd->ops->set_timeout(wdd, timeout);
        } else {
                wdd->timeout = timeout;
                /* Disable pretimeout if it doesn't fit the new timeout */
                if (wdd->pretimeout >= wdd->timeout)
                        wdd->pretimeout = 0;
        }

        watchdog_update_worker(wdd);

        return err;
}

/*
 *      watchdog_set_pretimeout: set the watchdog timer pretimeout
 *      @wdd: the watchdog device to set the timeout for
 *      @timeout: pretimeout to set in seconds
 */

static int watchdog_set_pretimeout(struct watchdog_device *wdd,
                                   unsigned int timeout)
{
        int err = 0;

        if (!(wdd->info->options & WDIOF_PRETIMEOUT))
                return -EOPNOTSUPP;

        if (watchdog_pretimeout_invalid(wdd, timeout))
                return -EINVAL;

        if (wdd->ops->set_pretimeout)
                err = wdd->ops->set_pretimeout(wdd, timeout);
        else
                wdd->pretimeout = timeout;

        return err;
}

/*
 *      watchdog_get_timeleft: wrapper to get the time left before a reboot
 *      @wdd: the watchdog device to get the remaining time from
 *      @timeleft: the time that's left
 *
 *      The caller must hold wd_data->lock.
 *
 *      Get the time before a watchdog will reboot (if not pinged).
 */

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

        if (!wdd->ops->get_timeleft)
                return -EOPNOTSUPP;

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

        return 0;
}

#ifdef CONFIG_WATCHDOG_SYSFS
static ssize_t nowayout_show(struct device *dev, struct device_attribute *attr,
                                char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);

        return sprintf(buf, "%d\n", !!test_bit(WDOG_NO_WAY_OUT, &wdd->status));
}
static DEVICE_ATTR_RO(nowayout);

static ssize_t status_show(struct device *dev, struct device_attribute *attr,
                                char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);
        struct watchdog_core_data *wd_data = wdd->wd_data;
        unsigned int status;

        mutex_lock(&wd_data->lock);
        status = watchdog_get_status(wdd);
        mutex_unlock(&wd_data->lock);

        return sprintf(buf, "0x%x\n", status);
}
static DEVICE_ATTR_RO(status);

static ssize_t bootstatus_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);

        return sprintf(buf, "%u\n", wdd->bootstatus);
}
static DEVICE_ATTR_RO(bootstatus);

static ssize_t timeleft_show(struct device *dev, struct device_attribute *attr,
                                char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);
        struct watchdog_core_data *wd_data = wdd->wd_data;
        ssize_t status;
        unsigned int val;

        mutex_lock(&wd_data->lock);
        status = watchdog_get_timeleft(wdd, &val);
        mutex_unlock(&wd_data->lock);
        if (!status)
                status = sprintf(buf, "%u\n", val);

        return status;
}
static DEVICE_ATTR_RO(timeleft);

static ssize_t timeout_show(struct device *dev, struct device_attribute *attr,
                                char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);

        return sprintf(buf, "%u\n", wdd->timeout);
}
static DEVICE_ATTR_RO(timeout);

static ssize_t pretimeout_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);

        return sprintf(buf, "%u\n", wdd->pretimeout);
}
static DEVICE_ATTR_RO(pretimeout);

static ssize_t identity_show(struct device *dev, struct device_attribute *attr,
                                char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);

        return sprintf(buf, "%s\n", wdd->info->identity);
}
static DEVICE_ATTR_RO(identity);

static ssize_t state_show(struct device *dev, struct device_attribute *attr,
                                char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);

        if (watchdog_active(wdd))
                return sprintf(buf, "active\n");

        return sprintf(buf, "inactive\n");
}
static DEVICE_ATTR_RO(state);

static ssize_t pretimeout_available_governors_show(struct device *dev,
                                   struct device_attribute *attr, char *buf)
{
        return watchdog_pretimeout_available_governors_get(buf);
}
static DEVICE_ATTR_RO(pretimeout_available_governors);

static ssize_t pretimeout_governor_show(struct device *dev,
                                        struct device_attribute *attr,
                                        char *buf)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);

        return watchdog_pretimeout_governor_get(wdd, buf);
}

static ssize_t pretimeout_governor_store(struct device *dev,
                                         struct device_attribute *attr,
                                         const char *buf, size_t count)
{
        struct watchdog_device *wdd = dev_get_drvdata(dev);
        int ret = watchdog_pretimeout_governor_set(wdd, buf);

        if (!ret)
                ret = count;

        return ret;
}
static DEVICE_ATTR_RW(pretimeout_governor);

static umode_t wdt_is_visible(struct kobject *kobj, struct attribute *attr,
                                int n)
{
        struct device *dev = container_of(kobj, struct device, kobj);
        struct watchdog_device *wdd = dev_get_drvdata(dev);
        umode_t mode = attr->mode;

        if (attr == &dev_attr_timeleft.attr && !wdd->ops->get_timeleft)
                mode = 0;
        else if (attr == &dev_attr_pretimeout.attr &&
                 !(wdd->info->options & WDIOF_PRETIMEOUT))
                mode = 0;
        else if ((attr == &dev_attr_pretimeout_governor.attr ||
                  attr == &dev_attr_pretimeout_available_governors.attr) &&
                 (!(wdd->info->options & WDIOF_PRETIMEOUT) ||
                  !IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_GOV)))
                mode = 0;

        return mode;
}
static struct attribute *wdt_attrs[] = {
        &dev_attr_state.attr,
        &dev_attr_identity.attr,
        &dev_attr_timeout.attr,
        &dev_attr_pretimeout.attr,
        &dev_attr_timeleft.attr,
        &dev_attr_bootstatus.attr,
        &dev_attr_status.attr,
        &dev_attr_nowayout.attr,
        &dev_attr_pretimeout_governor.attr,
        &dev_attr_pretimeout_available_governors.attr,
        NULL,
};

static const struct attribute_group wdt_group = {
        .attrs = wdt_attrs,
        .is_visible = wdt_is_visible,
};
__ATTRIBUTE_GROUPS(wdt);
#else
#define wdt_groups      NULL
#endif

/*
 *      watchdog_ioctl_op: call the watchdog drivers ioctl op if defined
 *      @wdd: the watchdog device to do the ioctl on
 *      @cmd: watchdog command
 *      @arg: argument pointer
 *
 *      The caller must hold wd_data->lock.
 */

static int watchdog_ioctl_op(struct watchdog_device *wdd, unsigned int cmd,
                                                        unsigned long arg)
{
        if (!wdd->ops->ioctl)
                return -ENOIOCTLCMD;

        return wdd->ops->ioctl(wdd, cmd, arg);
}

/*
 *      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_core_data *wd_data = file->private_data;
        struct watchdog_device *wdd;
        int err;
        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, &wd_data->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, &wd_data->status);
        }

        /* someone wrote to us, so we send the watchdog a keepalive ping */

        err = -ENODEV;
        mutex_lock(&wd_data->lock);
        wdd = wd_data->wdd;
        if (wdd)
                err = watchdog_ping(wdd);
        mutex_unlock(&wd_data->lock);

        if (err < 0)
                return err;

        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_core_data *wd_data = file->private_data;
        void __user *argp = (void __user *)arg;
        struct watchdog_device *wdd;
        int __user *p = argp;
        unsigned int val;
        int err;

        mutex_lock(&wd_data->lock);

        wdd = wd_data->wdd;
        if (!wdd) {
                err = -ENODEV;
                goto out_ioctl;
        }

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

        switch (cmd) {
        case WDIOC_GETSUPPORT:
                err = copy_to_user(argp, wdd->info,
                        sizeof(struct watchdog_info)) ? -EFAULT : 0;
                break;
        case WDIOC_GETSTATUS:
                val = watchdog_get_status(wdd);
                err = put_user(val, p);
                break;
        case WDIOC_GETBOOTSTATUS:
                err = put_user(wdd->bootstatus, p);
                break;
        case WDIOC_SETOPTIONS:
                if (get_user(val, p)) {
                        err = -EFAULT;
                        break;
                }
                if (val & WDIOS_DISABLECARD) {
                        err = watchdog_stop(wdd);
                        if (err < 0)
                                break;
                }
                if (val & WDIOS_ENABLECARD)
                        err = watchdog_start(wdd);
                break;
        case WDIOC_KEEPALIVE:
                if (!(wdd->info->options & WDIOF_KEEPALIVEPING)) {
                        err = -EOPNOTSUPP;
                        break;
                }
                err = watchdog_ping(wdd);
                break;
        case WDIOC_SETTIMEOUT:
                if (get_user(val, p)) {
                        err = -EFAULT;
                        break;
                }
                err = watchdog_set_timeout(wdd, val);
                if (err < 0)
                        break;
                /* 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) */
                err = watchdog_ping(wdd);
                if (err < 0)
                        break;
                /* Fall */
        case WDIOC_GETTIMEOUT:
                /* timeout == 0 means that we don't know the timeout */
                if (wdd->timeout == 0) {
                        err = -EOPNOTSUPP;
                        break;
                }
                err = put_user(wdd->timeout, p);
                break;
        case WDIOC_GETTIMELEFT:
                err = watchdog_get_timeleft(wdd, &val);
                if (err < 0)
                        break;
                err = put_user(val, p);
                break;
        case WDIOC_SETPRETIMEOUT:
                if (get_user(val, p)) {
                        err = -EFAULT;
                        break;
                }
                err = watchdog_set_pretimeout(wdd, val);
                break;
        case WDIOC_GETPRETIMEOUT:
                err = put_user(wdd->pretimeout, p);
                break;
        default:
                err = -ENOTTY;
                break;
        }

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

/*
 *      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)
{
        struct watchdog_core_data *wd_data;
        struct watchdog_device *wdd;
        int err;

        /* Get the corresponding watchdog device */
        if (imajor(inode) == MISC_MAJOR)
                wd_data = old_wd_data;
        else
                wd_data = container_of(inode->i_cdev, struct watchdog_core_data,
                                       cdev);

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

        wdd = wd_data->wdd;

        /*
         * If the /dev/watchdog device is open, we don't want the module
         * to be unloaded.
         */
        if (!watchdog_hw_running(wdd) && !try_module_get(wdd->ops->owner)) {
                err = -EBUSY;
                goto out_clear;
        }

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

        file->private_data = wd_data;

        if (!watchdog_hw_running(wdd))
                kref_get(&wd_data->kref);

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

out_mod:
        module_put(wd_data->wdd->ops->owner);
out_clear:
        clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
        return err;
}

static void watchdog_core_data_release(struct kref *kref)
{
        struct watchdog_core_data *wd_data;

        wd_data = container_of(kref, struct watchdog_core_data, kref);

        kfree(wd_data);
}

/*
 *      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_core_data *wd_data = file->private_data;
        struct watchdog_device *wdd;
        int err = -EBUSY;
        bool running;

        mutex_lock(&wd_data->lock);

        wdd = wd_data->wdd;
        if (!wdd)
                goto done;

        /*
         * 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_bit(WDOG_ACTIVE, &wdd->status))
                err = 0;
        else if (test_and_clear_bit(_WDOG_ALLOW_RELEASE, &wd_data->status) ||
                 !(wdd->info->options & WDIOF_MAGICCLOSE))
                err = watchdog_stop(wdd);

        /* If the watchdog was not stopped, send a keepalive ping */
        if (err < 0) {
                pr_crit("watchdog%d: watchdog did not stop!\n", wdd->id);
                watchdog_ping(wdd);
        }

        watchdog_update_worker(wdd);

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

done:
        running = wdd && watchdog_hw_running(wdd);
        mutex_unlock(&wd_data->lock);
        /*
         * Allow the owner module to be unloaded again unless the watchdog
         * is still running. If the watchdog is still running, it can not
         * be stopped, and its driver must not be unloaded.
         */
        if (!running) {
                module_put(wd_data->cdev.owner);
                kref_put(&wd_data->kref, watchdog_core_data_release);
        }
        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_cdev_register: register watchdog character device
 *      @wdd: watchdog device
 *      @devno: character device number
 *
 *      Register a watchdog character device including handling the legacy
 *      /dev/watchdog node. /dev/watchdog is actually a miscdevice and
 *      thus we set it up like that.
 */

static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
{
        struct watchdog_core_data *wd_data;
        int err;

        wd_data = kzalloc(sizeof(struct watchdog_core_data), GFP_KERNEL);
        if (!wd_data)
                return -ENOMEM;
        kref_init(&wd_data->kref);
        mutex_init(&wd_data->lock);

        wd_data->wdd = wdd;
        wdd->wd_data = wd_data;

        if (!watchdog_wq)
                return -ENODEV;

        INIT_DELAYED_WORK(&wd_data->work, watchdog_ping_work);

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

        /* Fill in the data structures */
        cdev_init(&wd_data->cdev, &watchdog_fops);
        wd_data->cdev.owner = wdd->ops->owner;

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

        /* Record time of most recent heartbeat as 'just before now'. */
        wd_data->last_hw_keepalive = jiffies - 1;

        /*
         * If the watchdog is running, prevent its driver from being unloaded,
         * and schedule an immediate ping.
         */
        if (watchdog_hw_running(wdd)) {
                if (handle_boot_enabled) {
                        __module_get(wdd->ops->owner);
                        kref_get(&wd_data->kref);
                        queue_delayed_work(watchdog_wq, &wd_data->work, 0);
                } else {
                        pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n",
                                        wdd->id);
                }
        }

        return 0;
}

/*
 *      watchdog_cdev_unregister: unregister watchdog character device
 *      @watchdog: watchdog device
 *
 *      Unregister watchdog character device and if needed the legacy
 *      /dev/watchdog device.
 */

static void watchdog_cdev_unregister(struct watchdog_device *wdd)
{
        struct watchdog_core_data *wd_data = wdd->wd_data;

        cdev_del(&wd_data->cdev);
        if (wdd->id == 0) {
                misc_deregister(&watchdog_miscdev);
                old_wd_data = NULL;
        }

        mutex_lock(&wd_data->lock);
        wd_data->wdd = NULL;
        wdd->wd_data = NULL;
        mutex_unlock(&wd_data->lock);

        if (watchdog_active(wdd) &&
            test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) {
                watchdog_stop(wdd);
        }

        cancel_delayed_work_sync(&wd_data->work);

        kref_put(&wd_data->kref, watchdog_core_data_release);
}

static struct class watchdog_class = {
        .name =         "watchdog",
        .owner =        THIS_MODULE,
        .dev_groups =   wdt_groups,
};

/*
 *      watchdog_dev_register: register a watchdog device
 *      @wdd: 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 *wdd)
{
        struct device *dev;
        dev_t devno;
        int ret;

        devno = MKDEV(MAJOR(watchdog_devt), wdd->id);

        ret = watchdog_cdev_register(wdd, devno);
        if (ret)
                return ret;

        dev = device_create_with_groups(&watchdog_class, wdd->parent,
                                        devno, wdd, wdd->groups,
                                        "watchdog%d", wdd->id);
        if (IS_ERR(dev)) {
                watchdog_cdev_unregister(wdd);
                return PTR_ERR(dev);
        }

        ret = watchdog_register_pretimeout(wdd);
        if (ret) {
                device_destroy(&watchdog_class, devno);
                watchdog_cdev_unregister(wdd);
        }

        return ret;
}

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

void watchdog_dev_unregister(struct watchdog_device *wdd)
{
        watchdog_unregister_pretimeout(wdd);
        device_destroy(&watchdog_class, wdd->wd_data->cdev.dev);
        watchdog_cdev_unregister(wdd);
}

/*
 *      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;

        watchdog_wq = alloc_workqueue("watchdogd",
                                      WQ_HIGHPRI | WQ_MEM_RECLAIM, 0);
        if (!watchdog_wq) {
                pr_err("Failed to create watchdog workqueue\n");
                return -ENOMEM;
        }

        err = class_register(&watchdog_class);
        if (err < 0) {
                pr_err("couldn't register class\n");
                goto err_register;
        }

        err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
        if (err < 0) {
                pr_err("watchdog: unable to allocate char dev region\n");
                goto err_alloc;
        }

        return 0;

err_alloc:
        class_unregister(&watchdog_class);
err_register:
        destroy_workqueue(watchdog_wq);
        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);
        class_unregister(&watchdog_class);
        destroy_workqueue(watchdog_wq);
}

module_param(handle_boot_enabled, bool, 0444);
MODULE_PARM_DESC(handle_boot_enabled,
        "Watchdog core auto-updates boot enabled watchdogs before userspace takes over (default="
        __MODULE_STRING(IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED)) ")");