/*
   *	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!
  ");
  		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 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
  ", timeout);
  		}
  
  		ret = misc_register(&xen_wdt_miscdev);
  		if (ret) {
  			pr_err("cannot register miscdev on minor=%d (%d)
  ",
  			       WATCHDOG_MINOR, ret);
  			break;
  		}
  
  		pr_info("initialized (timeout=%ds, nowayout=%d)
  ",
  			timeout, nowayout);
  		break;
  
  	case -ENOSYS:
  		pr_info("not supported
  ");
  		ret = -ENODEV;
  		break;
  
  	default:
  		pr_info("bogus return value %d
  ", ret);
  		break;
  	}
  
  	return ret;
  }
  
  static int 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         = 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
  ", 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
  ");
  }
  
  module_init(xen_wdt_init_module);
  module_exit(xen_wdt_cleanup_module);
  
  MODULE_AUTHOR("Jan Beulich <jbeulich@novell.com>");
  MODULE_DESCRIPTION("Xen WatchDog Timer Driver");
  MODULE_VERSION(DRV_VERSION);
  MODULE_LICENSE("GPL");