4 * (c) Copyright 2008-2011 Alan Cox <alan@lxorguk.ukuu.org.uk>,
7 * (c) Copyright 2008-2011 Wim Van Sebroeck <wim@iguana.be>.
10 * This source code is part of the generic code that can be used
11 * by all the watchdog timer drivers.
13 * This part of the generic code takes care of the following
14 * misc device: /dev/watchdog.
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>
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.
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.
33 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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/... */
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;
51 * watchdog_ping: ping the watchdog.
52 * @wddev: the watchdog device to ping
54 * If the watchdog has no own ping operation then it needs to be
55 * restarted via the start operation. This wrapper function does
59 static int watchdog_ping(struct watchdog_device *wddev)
62 return wddev->ops->ping(wddev); /* ping the watchdog */
64 return wddev->ops->start(wddev); /* restart the watchdog */
68 * watchdog_write: writes to the watchdog.
69 * @file: file from VFS
70 * @data: user address of data
71 * @len: length of data
72 * @ppos: pointer to the file offset
74 * A write to a watchdog device is defined as a keepalive ping.
77 static ssize_t watchdog_write(struct file *file, const char __user *data,
78 size_t len, loff_t *ppos)
86 for (i = 0; i != len; i++) {
87 if (get_user(c, data + i))
91 /* someone wrote to us, so we send the watchdog a keepalive ping */
98 * watchdog_open: open the /dev/watchdog device.
99 * @inode: inode of device
100 * @file: file handle to device
102 * When the /dev/watchdog device gets opened, we start the watchdog.
103 * Watch out: the /dev/watchdog device is single open, so we make sure
104 * it can only be opened once.
107 static int watchdog_open(struct inode *inode, struct file *file)
111 /* the watchdog is single open! */
112 if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status))
116 * If the /dev/watchdog device is open, we don't want the module
119 if (!try_module_get(wdd->ops->owner))
122 err = wdd->ops->start(wdd);
126 /* dev/watchdog is a virtual (and thus non-seekable) filesystem */
127 return nonseekable_open(inode, file);
130 module_put(wdd->ops->owner);
132 clear_bit(WDOG_DEV_OPEN, &wdd->status);
137 * watchdog_release: release the /dev/watchdog device.
138 * @inode: inode of device
139 * @file: file handle to device
141 * This is the code for when /dev/watchdog gets closed.
144 static int watchdog_release(struct inode *inode, struct file *file)
148 err = wdd->ops->stop(wdd);
150 pr_crit("%s: watchdog did not stop!\n", wdd->info->identity);
154 /* Allow the owner module to be unloaded again */
155 module_put(wdd->ops->owner);
157 /* make sure that /dev/watchdog can be re-opened */
158 clear_bit(WDOG_DEV_OPEN, &wdd->status);
163 static const struct file_operations watchdog_fops = {
164 .owner = THIS_MODULE,
165 .write = watchdog_write,
166 .open = watchdog_open,
167 .release = watchdog_release,
170 static struct miscdevice watchdog_miscdev = {
171 .minor = WATCHDOG_MINOR,
173 .fops = &watchdog_fops,
177 * watchdog_dev_register:
178 * @watchdog: watchdog device
180 * Register a watchdog device as /dev/watchdog. /dev/watchdog
181 * is actually a miscdevice and thus we set it up like that.
184 int watchdog_dev_register(struct watchdog_device *watchdog)
188 /* Only one device can register for /dev/watchdog */
189 if (test_and_set_bit(0, &watchdog_dev_busy)) {
190 pr_err("only one watchdog can use /dev/watchdog.\n");
196 err = misc_register(&watchdog_miscdev);
198 pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
199 watchdog->info->identity, WATCHDOG_MINOR, err);
207 clear_bit(0, &watchdog_dev_busy);
212 * watchdog_dev_unregister:
213 * @watchdog: watchdog device
215 * Deregister the /dev/watchdog device.
218 int watchdog_dev_unregister(struct watchdog_device *watchdog)
220 /* Check that a watchdog device was registered in the past */
221 if (!test_bit(0, &watchdog_dev_busy) || !wdd)
224 /* We can only unregister the watchdog device that was registered */
225 if (watchdog != wdd) {
226 pr_err("%s: watchdog was not registered as /dev/watchdog.\n",
227 watchdog->info->identity);
231 misc_deregister(&watchdog_miscdev);
233 clear_bit(0, &watchdog_dev_busy);