/*
* 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.
*/
static int watchdog_ping(struct watchdog_device *wddev)
{
if (wddev->ops->ping)
return wddev->ops->ping(wddev); /* ping the watchdog */
else
return wddev->ops->start(wddev); /* restart the watchdog */
}
/*
* 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.
*/
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;
for (i = 0; i != len; i++) {
if (get_user(c, data + i))
return -EFAULT;
}
/* someone wrote to us, so we send the watchdog a keepalive ping */
watchdog_ping(wdd);
return len;
}
/*
* 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 = wdd->ops->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.
*/
static int watchdog_release(struct inode *inode, struct file *file)
{
int err;
err = wdd->ops->stop(wdd);
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,
.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;
}
