[deliverable/linux.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/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/... */

/* make sure we only register one /dev/watchdog device */
static unsigned long watchdog_dev_busy;
/* the watchdog device behind /dev/watchdog */
static struct watchdog_device *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)
{
	if (test_bit(WDOG_ACTIVE, &wddev->status)) {
		if (wddev->ops->ping)
			return wddev->ops->ping(wddev);  /* ping the watchdog */
		else
			return wddev->ops->start(wddev); /* restart watchdog */
	}
	return 0;
}

/*
 *	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;

	if (!test_bit(WDOG_ACTIVE, &wddev->status)) {
		err = wddev->ops->start(wddev);
		if (err < 0)
			return err;

		set_bit(WDOG_ACTIVE, &wddev->status);
	}
	return 0;
}

/*
 *	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 = -EBUSY;

	if (test_bit(WDOG_NO_WAY_OUT, &wddev->status)) {
		pr_info("%s: nowayout prevents watchdog to be stopped!\n",
							wddev->info->identity);
		return err;
	}

	if (test_bit(WDOG_ACTIVE, &wddev->status)) {
		err = wddev->ops->stop(wddev);
		if (err < 0)
			return err;

		clear_bit(WDOG_ACTIVE, &wddev->status);
	}
	return 0;
}

/*
 *	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)
{
	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)
{
	void __user *argp = (void __user *)arg;
	int __user *p = argp;
	unsigned int val;
	int err;

	if (wdd->ops->ioctl) {
		err = wdd->ops->ioctl(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:
		val = wdd->ops->status ? wdd->ops->status(wdd) : 0;
		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 ((wdd->ops->set_timeout == NULL) ||
		    !(wdd->info->options & WDIOF_SETTIMEOUT))
			return -EOPNOTSUPP;
		if (get_user(val, p))
			return -EFAULT;
		if ((wdd->max_timeout != 0) &&
		    (val < wdd->min_timeout || val > wdd->max_timeout))
				return -EINVAL;
		err = wdd->ops->set_timeout(wdd, val);
		if (err < 0)
			return err;
		wdd->timeout = val;
		/* 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);
	default:
		return -ENOTTY;
	}
}

/*
 *	watchdog_open: open the /dev/watchdog device.
 *	@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;

	/* 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;

	/* 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 /dev/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)
{
	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) {
		pr_crit("%s: watchdog did not stop!\n", wdd->info->identity);
		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);

	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:
 *	@watchdog: watchdog device
 *
 *	Register a watchdog device as /dev/watchdog. /dev/watchdog
 *	is actually a miscdevice and thus we set it up like that.
 */

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

	/* Only one device can register for /dev/watchdog */
	if (test_and_set_bit(0, &watchdog_dev_busy)) {
		pr_err("only one watchdog can use /dev/watchdog\n");
		return -EBUSY;
	}

	wdd = watchdog;

	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);
		goto out;
	}

	return 0;

out:
	wdd = NULL;
	clear_bit(0, &watchdog_dev_busy);
	return err;
}

/*
 *	watchdog_dev_unregister:
 *	@watchdog: watchdog device
 *
 *	Deregister the /dev/watchdog device.
 */

int watchdog_dev_unregister(struct watchdog_device *watchdog)
{
	/* Check that a watchdog device was registered in the past */
	if (!test_bit(0, &watchdog_dev_busy) || !wdd)
		return -ENODEV;

	/* We can only unregister the watchdog device that was registered */
	if (watchdog != wdd) {
		pr_err("%s: watchdog was not registered as /dev/watchdog\n",
		       watchdog->info->identity);
		return -ENODEV;
	}

	misc_deregister(&watchdog_miscdev);
	wdd = NULL;
	clear_bit(0, &watchdog_dev_busy);
	return 0;
}
Commit	Line	Data
43316044 WVS	1	/*
	2	* watchdog_dev.c
	3	*
	4	* (c) Copyright 2008-2011 Alan Cox <alan@lxorguk.ukuu.org.uk>,
	5	* All Rights Reserved.
	6	*
	7	* (c) Copyright 2008-2011 Wim Van Sebroeck <wim@iguana.be>.
	8	*
	9	*
	10	* This source code is part of the generic code that can be used
	11	* by all the watchdog timer drivers.
	12	*
	13	* This part of the generic code takes care of the following
	14	* misc device: /dev/watchdog.
	15	*
	16	* Based on source code of the following authors:
	17	* Matt Domsch <Matt_Domsch@dell.com>,
	18	* Rob Radez <rob@osinvestor.com>,
	19	* Rusty Lynch <rusty@linux.co.intel.com>
	20	* Satyam Sharma <satyam@infradead.org>
	21	* Randy Dunlap <randy.dunlap@oracle.com>
	22	*
	23	* This program is free software; you can redistribute it and/or
	24	* modify it under the terms of the GNU General Public License
	25	* as published by the Free Software Foundation; either version
	26	* 2 of the License, or (at your option) any later version.
	27	*
	28	* Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
	29	* admit liability nor provide warranty for any of this software.
	30	* This material is provided "AS-IS" and at no charge.
	31	*/
	32
	33	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
	34
	35	#include <linux/module.h> /* For module stuff/... */
	36	#include <linux/types.h> /* For standard types (like size_t) */
	37	#include <linux/errno.h> /* For the -ENODEV/... values */
	38	#include <linux/kernel.h> /* For printk/panic/... */
	39	#include <linux/fs.h> /* For file operations */
	40	#include <linux/watchdog.h> /* For watchdog specific items */
	41	#include <linux/miscdevice.h> /* For handling misc devices */
	42	#include <linux/init.h> /* For __init/__exit/... */
	43	#include <linux/uaccess.h> /* For copy_to_user/put_user/... */
	44
	45	/* make sure we only register one /dev/watchdog device */
	46	static unsigned long watchdog_dev_busy;
	47	/* the watchdog device behind /dev/watchdog */
	48	static struct watchdog_device *wdd;
	49
	50	/*
	51	* watchdog_ping: ping the watchdog.
	52	* @wddev: the watchdog device to ping
	53	*
	54	* If the watchdog has no own ping operation then it needs to be
	55	* restarted via the start operation. This wrapper function does
	56	* exactly that.
234445b4	57	* We only ping when the watchdog device is running.
43316044 WVS	58	*/
	59
	60	static int watchdog_ping(struct watchdog_device *wddev)
	61	{
cb7efc02	62	if (test_bit(WDOG_ACTIVE, &wddev->status)) {
234445b4 WVS	63	if (wddev->ops->ping)
	64	return wddev->ops->ping(wddev); /* ping the watchdog */
	65	else
	66	return wddev->ops->start(wddev); /* restart watchdog */
	67	}
	68	return 0;
	69	}
	70
	71	/*
	72	* watchdog_start: wrapper to start the watchdog.
	73	* @wddev: the watchdog device to start
	74	*
	75	* Start the watchdog if it is not active and mark it active.
	76	* This function returns zero on success or a negative errno code for
	77	* failure.
	78	*/
	79
	80	static int watchdog_start(struct watchdog_device *wddev)
	81	{
	82	int err;
	83
cb7efc02	84	if (!test_bit(WDOG_ACTIVE, &wddev->status)) {
234445b4 WVS	85	err = wddev->ops->start(wddev);
	86	if (err < 0)
	87	return err;
	88
cb7efc02	89	set_bit(WDOG_ACTIVE, &wddev->status);
234445b4 WVS	90	}
	91	return 0;
	92	}
	93
	94	/*
	95	* watchdog_stop: wrapper to stop the watchdog.
	96	* @wddev: the watchdog device to stop
	97	*
	98	* Stop the watchdog if it is still active and unmark it active.
	99	* This function returns zero on success or a negative errno code for
	100	* failure.
7e192b9c	101	* If the 'nowayout' feature was set, the watchdog cannot be stopped.
234445b4 WVS	102	*/
	103
	104	static int watchdog_stop(struct watchdog_device *wddev)
	105	{
7e192b9c WVS	106	int err = -EBUSY;
7e192b9c WVS	107
cb7efc02	108	if (test_bit(WDOG_NO_WAY_OUT, &wddev->status)) {
7e192b9c	109	pr_info("%s: nowayout prevents watchdog to be stopped!\n",
cb7efc02	110	wddev->info->identity);
7e192b9c WVS	111	return err;
7e192b9c WVS	112	}
234445b4	113
cb7efc02	114	if (test_bit(WDOG_ACTIVE, &wddev->status)) {
234445b4 WVS	115	err = wddev->ops->stop(wddev);
	116	if (err < 0)
	117	return err;
	118
cb7efc02	119	clear_bit(WDOG_ACTIVE, &wddev->status);
234445b4 WVS	120	}
234445b4 WVS	121	return 0;
43316044 WVS	122	}
	123
	124	/*
	125	* watchdog_write: writes to the watchdog.
	126	* @file: file from VFS
	127	* @data: user address of data
	128	* @len: length of data
	129	* @ppos: pointer to the file offset
	130	*
	131	* A write to a watchdog device is defined as a keepalive ping.
017cf080	132	* Writing the magic 'V' sequence allows the next close to turn
7e192b9c	133	* off the watchdog (if 'nowayout' is not set).
43316044 WVS	134	*/
	135
	136	static ssize_t watchdog_write(struct file file, const char __user data,
	137	size_t len, loff_t *ppos)
	138	{
	139	size_t i;
	140	char c;
	141
	142	if (len == 0)
	143	return 0;
	144
017cf080 WVS	145	/*
	146	* Note: just in case someone wrote the magic character
	147	* five months ago...
	148	*/
	149	clear_bit(WDOG_ALLOW_RELEASE, &wdd->status);
	150
	151	/* scan to see whether or not we got the magic character */
43316044 WVS	152	for (i = 0; i != len; i++) {
	153	if (get_user(c, data + i))
	154	return -EFAULT;
017cf080 WVS	155	if (c == 'V')
017cf080 WVS	156	set_bit(WDOG_ALLOW_RELEASE, &wdd->status);
43316044 WVS	157	}
	158
	159	/* someone wrote to us, so we send the watchdog a keepalive ping */
	160	watchdog_ping(wdd);
	161
	162	return len;
	163	}
	164
2fa03560 WVS	165	/*
	166	* watchdog_ioctl: handle the different ioctl's for the watchdog device.
	167	* @file: file handle to the device
	168	* @cmd: watchdog command
	169	* @arg: argument pointer
	170	*
	171	* The watchdog API defines a common set of functions for all watchdogs
	172	* according to their available features.
	173	*/
	174
	175	static long watchdog_ioctl(struct file *file, unsigned int cmd,
	176	unsigned long arg)
	177	{
	178	void __user argp = (void __user )arg;
	179	int __user *p = argp;
	180	unsigned int val;
234445b4	181	int err;
2fa03560	182
78d88fc0 WVS	183	if (wdd->ops->ioctl) {
	184	err = wdd->ops->ioctl(wdd, cmd, arg);
	185	if (err != -ENOIOCTLCMD)
	186	return err;
	187	}
	188
2fa03560 WVS	189	switch (cmd) {
	190	case WDIOC_GETSUPPORT:
	191	return copy_to_user(argp, wdd->info,
	192	sizeof(struct watchdog_info)) ? -EFAULT : 0;
	193	case WDIOC_GETSTATUS:
	194	val = wdd->ops->status ? wdd->ops->status(wdd) : 0;
	195	return put_user(val, p);
	196	case WDIOC_GETBOOTSTATUS:
	197	return put_user(wdd->bootstatus, p);
234445b4 WVS	198	case WDIOC_SETOPTIONS:
	199	if (get_user(val, p))
	200	return -EFAULT;
	201	if (val & WDIOS_DISABLECARD) {
	202	err = watchdog_stop(wdd);
	203	if (err < 0)
	204	return err;
	205	}
	206	if (val & WDIOS_ENABLECARD) {
	207	err = watchdog_start(wdd);
	208	if (err < 0)
	209	return err;
	210	}
	211	return 0;
c2dc00e4 WVS	212	case WDIOC_KEEPALIVE:
	213	if (!(wdd->info->options & WDIOF_KEEPALIVEPING))
	214	return -EOPNOTSUPP;
	215	watchdog_ping(wdd);
	216	return 0;
014d694e WVS	217	case WDIOC_SETTIMEOUT:
	218	if ((wdd->ops->set_timeout == NULL) \|\|
	219	!(wdd->info->options & WDIOF_SETTIMEOUT))
	220	return -EOPNOTSUPP;
	221	if (get_user(val, p))
	222	return -EFAULT;
3f43f68e WVS	223	if ((wdd->max_timeout != 0) &&
	224	(val < wdd->min_timeout \|\| val > wdd->max_timeout))
	225	return -EINVAL;
014d694e WVS	226	err = wdd->ops->set_timeout(wdd, val);
	227	if (err < 0)
	228	return err;
	229	wdd->timeout = val;
	230	/* If the watchdog is active then we send a keepalive ping
	231	* to make sure that the watchdog keep's running (and if
	232	* possible that it takes the new timeout) */
	233	watchdog_ping(wdd);
	234	/* Fall */
	235	case WDIOC_GETTIMEOUT:
	236	/* timeout == 0 means that we don't know the timeout */
	237	if (wdd->timeout == 0)
	238	return -EOPNOTSUPP;
	239	return put_user(wdd->timeout, p);
2fa03560 WVS	240	default:
	241	return -ENOTTY;
	242	}
	243	}
	244
43316044 WVS	245	/*
	246	* watchdog_open: open the /dev/watchdog device.
	247	* @inode: inode of device
	248	* @file: file handle to device
	249	*
	250	* When the /dev/watchdog device gets opened, we start the watchdog.
	251	* Watch out: the /dev/watchdog device is single open, so we make sure
	252	* it can only be opened once.
	253	*/
	254
	255	static int watchdog_open(struct inode inode, struct file file)
	256	{
	257	int err = -EBUSY;
	258
	259	/* the watchdog is single open! */
	260	if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status))
	261	return -EBUSY;
	262
	263	/*
	264	* If the /dev/watchdog device is open, we don't want the module
	265	* to be unloaded.
	266	*/
	267	if (!try_module_get(wdd->ops->owner))
	268	goto out;
	269
234445b4	270	err = watchdog_start(wdd);
43316044 WVS	271	if (err < 0)
	272	goto out_mod;
	273
	274	/* dev/watchdog is a virtual (and thus non-seekable) filesystem */
	275	return nonseekable_open(inode, file);
	276
	277	out_mod:
	278	module_put(wdd->ops->owner);
	279	out:
	280	clear_bit(WDOG_DEV_OPEN, &wdd->status);
	281	return err;
	282	}
	283
	284	/*
	285	* watchdog_release: release the /dev/watchdog device.
	286	* @inode: inode of device
	287	* @file: file handle to device
	288	*
017cf080	289	* This is the code for when /dev/watchdog gets closed. We will only
7e192b9c WVS	290	* stop the watchdog when we have received the magic char (and nowayout
7e192b9c WVS	291	* was not set), else the watchdog will keep running.
43316044 WVS	292	*/
	293
	294	static int watchdog_release(struct inode inode, struct file file)
	295	{
017cf080 WVS	296	int err = -EBUSY;
	297
	298	/*
	299	* We only stop the watchdog if we received the magic character
7e192b9c WVS	300	* or if WDIOF_MAGICCLOSE is not set. If nowayout was set then
7e192b9c WVS	301	* watchdog_stop will fail.
017cf080 WVS	302	*/
	303	if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) \|\|
	304	!(wdd->info->options & WDIOF_MAGICCLOSE))
	305	err = watchdog_stop(wdd);
43316044	306
017cf080	307	/* If the watchdog was not stopped, send a keepalive ping */
234445b4	308	if (err < 0) {
43316044 WVS	309	pr_crit("%s: watchdog did not stop!\n", wdd->info->identity);
	310	watchdog_ping(wdd);
	311	}
	312
	313	/* Allow the owner module to be unloaded again */
	314	module_put(wdd->ops->owner);
	315
	316	/* make sure that /dev/watchdog can be re-opened */
	317	clear_bit(WDOG_DEV_OPEN, &wdd->status);
	318
	319	return 0;
	320	}
	321
	322	static const struct file_operations watchdog_fops = {
	323	.owner = THIS_MODULE,
	324	.write = watchdog_write,
2fa03560	325	.unlocked_ioctl = watchdog_ioctl,
43316044 WVS	326	.open = watchdog_open,
	327	.release = watchdog_release,
	328	};
	329
	330	static struct miscdevice watchdog_miscdev = {
	331	.minor = WATCHDOG_MINOR,
	332	.name = "watchdog",
	333	.fops = &watchdog_fops,
	334	};
	335
	336	/*
	337	* watchdog_dev_register:
	338	* @watchdog: watchdog device
	339	*
	340	* Register a watchdog device as /dev/watchdog. /dev/watchdog
	341	* is actually a miscdevice and thus we set it up like that.
	342	*/
	343
	344	int watchdog_dev_register(struct watchdog_device *watchdog)
	345	{
	346	int err;
	347
	348	/* Only one device can register for /dev/watchdog */
	349	if (test_and_set_bit(0, &watchdog_dev_busy)) {
27c766aa	350	pr_err("only one watchdog can use /dev/watchdog\n");
43316044 WVS	351	return -EBUSY;
	352	}
	353
	354	wdd = watchdog;
	355
	356	err = misc_register(&watchdog_miscdev);
	357	if (err != 0) {
27c766aa JP	358	pr_err("%s: cannot register miscdev on minor=%d (err=%d)\n",
27c766aa JP	359	watchdog->info->identity, WATCHDOG_MINOR, err);
43316044 WVS	360	goto out;
	361	}
	362
	363	return 0;
	364
	365	out:
	366	wdd = NULL;
	367	clear_bit(0, &watchdog_dev_busy);
	368	return err;
	369	}
	370
	371	/*
	372	* watchdog_dev_unregister:
	373	* @watchdog: watchdog device
	374	*
	375	* Deregister the /dev/watchdog device.
	376	*/
	377
	378	int watchdog_dev_unregister(struct watchdog_device *watchdog)
	379	{
	380	/* Check that a watchdog device was registered in the past */
	381	if (!test_bit(0, &watchdog_dev_busy) \|\| !wdd)
	382	return -ENODEV;
	383
	384	/* We can only unregister the watchdog device that was registered */
	385	if (watchdog != wdd) {
27c766aa JP	386	pr_err("%s: watchdog was not registered as /dev/watchdog\n",
27c766aa JP	387	watchdog->info->identity);
43316044 WVS	388	return -ENODEV;
	389	}
	390
	391	misc_deregister(&watchdog_miscdev);
	392	wdd = NULL;
	393	clear_bit(0, &watchdog_dev_busy);
	394	return 0;
	395	}