xen_wdt.c

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/*
 *  Xen Watchdog Driver
 *
 *  (c) Copyright 2010 Novell, Inc.
 *
 *  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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#define DRV_NAME    "wdt"
#define DRV_VERSION "0.01"

#include <linux/bug.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/hrtimer.h>
#include <linux/kernel.h>
#include <linux/ktime.h>
#include <linux/init.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/platform_device.h>
#include <linux/spinlock.h>
#include <linux/uaccess.h>
#include <linux/watchdog.h>
#include <xen/xen.h>
#include <asm/xen/hypercall.h>
#include <xen/interface/sched.h>

static struct platform_device *platform_device;
static DEFINE_SPINLOCK(wdt_lock);
static struct sched_watchdog wdt;
static __kernel_time_t wdt_expires;
static bool is_active, expect_release;

#define WATCHDOG_TIMEOUT 60 /* in seconds */
static unsigned int timeout = WATCHDOG_TIMEOUT;
module_param(timeout, uint, S_IRUGO);
MODULE_PARM_DESC(timeout, "Watchdog timeout in seconds "
    "(default=" __MODULE_STRING(WATCHDOG_TIMEOUT) ")");

static bool nowayout = WATCHDOG_NOWAYOUT;
module_param(nowayout, bool, S_IRUGO);
MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started "
    "(default=" __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");

static inline __kernel_time_t set_timeout(void)
{
    wdt.timeout = timeout;
    return ktime_to_timespec(ktime_get()).tv_sec + timeout;
}

static int xen_wdt_start(void)
{
    __kernel_time_t expires;
    int err;

    spin_lock(&wdt_lock);

    expires = set_timeout();
    if (!wdt.id)
        err = HYPERVISOR_sched_op(SCHEDOP_watchdog, &wdt);
    else
        err = -EBUSY;
    if (err > 0) {
        wdt.id = err;
        wdt_expires = expires;
        err = 0;
    } else
        BUG_ON(!err);

    spin_unlock(&wdt_lock);

    return err;
}

static int xen_wdt_stop(void)
{
    int err = 0;

    spin_lock(&wdt_lock);

    wdt.timeout = 0;
    if (wdt.id)
        err = HYPERVISOR_sched_op(SCHEDOP_watchdog, &wdt);
    if (!err)
        wdt.id = 0;

    spin_unlock(&wdt_lock);

    return err;
}

static int xen_wdt_kick(void)
{
    __kernel_time_t expires;
    int err;

    spin_lock(&wdt_lock);

    expires = set_timeout();
    if (wdt.id)
        err = HYPERVISOR_sched_op(SCHEDOP_watchdog, &wdt);
    else
        err = -ENXIO;
    if (!err)
        wdt_expires = expires;

    spin_unlock(&wdt_lock);

    return err;
}

static int xen_wdt_open(struct inode *inode, struct file *file)
{
    int err;

    /* /dev/watchdog can only be opened once */
    if (xchg(&is_active, true))
        return -EBUSY;

    err = xen_wdt_start();
    if (err == -EBUSY)
        err = xen_wdt_kick();
    return err ?: nonseekable_open(inode, file);
}

static int xen_wdt_release(struct inode *inode, struct file *file)
{
    int err = 0;

    if (expect_release)
        err = xen_wdt_stop();
    else {
        pr_crit("unexpected close, not stopping watchdog!\n");
        xen_wdt_kick();
    }
    is_active = err;
    expect_release = false;
    return err;
}

static ssize_t xen_wdt_write(struct file *file, const char __user *data,
                 size_t len, loff_t *ppos)
{
    /* See if we got the magic character 'V' and reload the timer */
    if (len) {
        if (!nowayout) {
            size_t i;

            /* in case it was set long ago */
            expect_release = false;

            /* scan to see whether or not we got the magic
               character */
            for (i = 0; i != len; i++) {
                char c;
                if (get_user(c, data + i))
                    return -EFAULT;
                if (c == 'V')
                    expect_release = true;
            }
        }

        /* someone wrote to us, we should reload the timer */
        xen_wdt_kick();
    }
    return len;
}

static long xen_wdt_ioctl(struct file *file, unsigned int cmd,
              unsigned long arg)
{
    int new_options, retval = -EINVAL;
    int new_timeout;
    int __user *argp = (void __user *)arg;
    static const struct watchdog_info ident = {
        .options =      WDIOF_SETTIMEOUT | WDIOF_MAGICCLOSE,
        .firmware_version = 0,
        .identity =     DRV_NAME,
    };

    switch (cmd) {
    case WDIOC_GETSUPPORT:
        return copy_to_user(argp, &ident, sizeof(ident)) ? -EFAULT : 0;

    case WDIOC_GETSTATUS:
    case WDIOC_GETBOOTSTATUS:
        return put_user(0, argp);

    case WDIOC_SETOPTIONS:
        if (get_user(new_options, argp))
            return -EFAULT;

        if (new_options & WDIOS_DISABLECARD)
            retval = xen_wdt_stop();
        if (new_options & WDIOS_ENABLECARD) {
            retval = xen_wdt_start();
            if (retval == -EBUSY)
                retval = xen_wdt_kick();
        }
        return retval;

    case WDIOC_KEEPALIVE:
        xen_wdt_kick();
        return 0;

    case WDIOC_SETTIMEOUT:
        if (get_user(new_timeout, argp))
            return -EFAULT;
        if (!new_timeout)
            return -EINVAL;
        timeout = new_timeout;
        xen_wdt_kick();
        /* fall through */
    case WDIOC_GETTIMEOUT:
        return put_user(timeout, argp);

    case WDIOC_GETTIMELEFT:
        retval = wdt_expires - ktime_to_timespec(ktime_get()).tv_sec;
        return put_user(retval, argp);
    }

    return -ENOTTY;
}

static const struct file_operations xen_wdt_fops = {
    .owner =        THIS_MODULE,
    .llseek =       no_llseek,
    .write =        xen_wdt_write,
    .unlocked_ioctl =   xen_wdt_ioctl,
    .open =         xen_wdt_open,
    .release =      xen_wdt_release,
};

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

static int __devinit xen_wdt_probe(struct platform_device *dev)
{
    struct sched_watchdog wd = { .id = ~0 };
    int ret = HYPERVISOR_sched_op(SCHEDOP_watchdog, &wd);

    switch (ret) {
    case -EINVAL:
        if (!timeout) {
            timeout = WATCHDOG_TIMEOUT;
            pr_info("timeout value invalid, using %d\n", timeout);
        }

        ret = misc_register(&xen_wdt_miscdev);
        if (ret) {
            pr_err("cannot register miscdev on minor=%d (%d)\n",
                   WATCHDOG_MINOR, ret);
            break;
        }

        pr_info("initialized (timeout=%ds, nowayout=%d)\n",
            timeout, nowayout);
        break;

    case -ENOSYS:
        pr_info("not supported\n");
        ret = -ENODEV;
        break;

    default:
        pr_info("bogus return value %d\n", ret);
        break;
    }

    return ret;
}

static int __devexit xen_wdt_remove(struct platform_device *dev)
{
    /* Stop the timer before we leave */
    if (!nowayout)
        xen_wdt_stop();

    misc_deregister(&xen_wdt_miscdev);

    return 0;
}

static void xen_wdt_shutdown(struct platform_device *dev)
{
    xen_wdt_stop();
}

static int xen_wdt_suspend(struct platform_device *dev, pm_message_t state)
{
    typeof(wdt.id) id = wdt.id;
    int rc = xen_wdt_stop();

    wdt.id = id;
    return rc;
}

static int xen_wdt_resume(struct platform_device *dev)
{
    if (!wdt.id)
        return 0;
    wdt.id = 0;
    return xen_wdt_start();
}

static struct platform_driver xen_wdt_driver = {
    .probe          = xen_wdt_probe,
    .remove         = __devexit_p(xen_wdt_remove),
    .shutdown       = xen_wdt_shutdown,
    .suspend        = xen_wdt_suspend,
    .resume         = xen_wdt_resume,
    .driver         = {
        .owner  = THIS_MODULE,
        .name   = DRV_NAME,
    },
};

static int __init xen_wdt_init_module(void)
{
    int err;

    if (!xen_domain())
        return -ENODEV;

    pr_info("Xen WatchDog Timer Driver v%s\n", DRV_VERSION);

    err = platform_driver_register(&xen_wdt_driver);
    if (err)
        return err;

    platform_device = platform_device_register_simple(DRV_NAME,
                                  -1, NULL, 0);
    if (IS_ERR(platform_device)) {
        err = PTR_ERR(platform_device);
        platform_driver_unregister(&xen_wdt_driver);
    }

    return err;
}

static void __exit xen_wdt_cleanup_module(void)
{
    platform_device_unregister(platform_device);
    platform_driver_unregister(&xen_wdt_driver);
    pr_info("module unloaded\n");
}

module_init(xen_wdt_init_module);
module_exit(xen_wdt_cleanup_module);

MODULE_AUTHOR("Jan Beulich <[email protected]>");
MODULE_DESCRIPTION("Xen WatchDog Timer Driver");
MODULE_VERSION(DRV_VERSION);
MODULE_LICENSE("GPL");
MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR);