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. 57 */ 58 59 static int watchdog_ping(struct watchdog_device *wddev) 60 { 61 if (wddev->ops->ping) 62 return wddev->ops->ping(wddev); /* ping the watchdog */ 63 else 64 return wddev->ops->start(wddev); /* restart the watchdog */ 65 } 66 67 /* 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 73 * 74 * A write to a watchdog device is defined as a keepalive ping. 75 */ 76 77 static ssize_t watchdog_write(struct file *file, const char __user *data, 78 size_t len, loff_t *ppos) 79 { 80 size_t i; 81 char c; 82 83 if (len == 0) 84 return 0; 85 86 for (i = 0; i != len; i++) { 87 if (get_user(c, data + i)) 88 return -EFAULT; 89 } 90 91 /* someone wrote to us, so we send the watchdog a keepalive ping */ 92 watchdog_ping(wdd); 93 94 return len; 95 } 96 97 /* 98 * watchdog_ioctl: handle the different ioctl's for the watchdog device. 99 * @file: file handle to the device 100 * @cmd: watchdog command 101 * @arg: argument pointer 102 * 103 * The watchdog API defines a common set of functions for all watchdogs 104 * according to their available features. 105 */ 106 107 static long watchdog_ioctl(struct file *file, unsigned int cmd, 108 unsigned long arg) 109 { 110 void __user *argp = (void __user *)arg; 111 int __user *p = argp; 112 unsigned int val; 113 114 switch (cmd) { 115 case WDIOC_GETSUPPORT: 116 return copy_to_user(argp, wdd->info, 117 sizeof(struct watchdog_info)) ? -EFAULT : 0; 118 case WDIOC_GETSTATUS: 119 val = wdd->ops->status ? wdd->ops->status(wdd) : 0; 120 return put_user(val, p); 121 case WDIOC_GETBOOTSTATUS: 122 return put_user(wdd->bootstatus, p); 123 default: 124 return -ENOTTY; 125 } 126 } 127 128 /* 129 * watchdog_open: open the /dev/watchdog device. 130 * @inode: inode of device 131 * @file: file handle to device 132 * 133 * When the /dev/watchdog device gets opened, we start the watchdog. 134 * Watch out: the /dev/watchdog device is single open, so we make sure 135 * it can only be opened once. 136 */ 137 138 static int watchdog_open(struct inode *inode, struct file *file) 139 { 140 int err = -EBUSY; 141 142 /* the watchdog is single open! */ 143 if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status)) 144 return -EBUSY; 145 146 /* 147 * If the /dev/watchdog device is open, we don't want the module 148 * to be unloaded. 149 */ 150 if (!try_module_get(wdd->ops->owner)) 151 goto out; 152 153 err = wdd->ops->start(wdd); 154 if (err < 0) 155 goto out_mod; 156 157 /* dev/watchdog is a virtual (and thus non-seekable) filesystem */ 158 return nonseekable_open(inode, file); 159 160 out_mod: 161 module_put(wdd->ops->owner); 162 out: 163 clear_bit(WDOG_DEV_OPEN, &wdd->status); 164 return err; 165 } 166 167 /* 168 * watchdog_release: release the /dev/watchdog device. 169 * @inode: inode of device 170 * @file: file handle to device 171 * 172 * This is the code for when /dev/watchdog gets closed. 173 */ 174 175 static int watchdog_release(struct inode *inode, struct file *file) 176 { 177 int err; 178 179 err = wdd->ops->stop(wdd); 180 if (err != 0) { 181 pr_crit("%s: watchdog did not stop!\n", wdd->info->identity); 182 watchdog_ping(wdd); 183 } 184 185 /* Allow the owner module to be unloaded again */ 186 module_put(wdd->ops->owner); 187 188 /* make sure that /dev/watchdog can be re-opened */ 189 clear_bit(WDOG_DEV_OPEN, &wdd->status); 190 191 return 0; 192 } 193 194 static const struct file_operations watchdog_fops = { 195 .owner = THIS_MODULE, 196 .write = watchdog_write, 197 .unlocked_ioctl = watchdog_ioctl, 198 .open = watchdog_open, 199 .release = watchdog_release, 200 }; 201 202 static struct miscdevice watchdog_miscdev = { 203 .minor = WATCHDOG_MINOR, 204 .name = "watchdog", 205 .fops = &watchdog_fops, 206 }; 207 208 /* 209 * watchdog_dev_register: 210 * @watchdog: watchdog device 211 * 212 * Register a watchdog device as /dev/watchdog. /dev/watchdog 213 * is actually a miscdevice and thus we set it up like that. 214 */ 215 216 int watchdog_dev_register(struct watchdog_device *watchdog) 217 { 218 int err; 219 220 /* Only one device can register for /dev/watchdog */ 221 if (test_and_set_bit(0, &watchdog_dev_busy)) { 222 pr_err("only one watchdog can use /dev/watchdog.\n"); 223 return -EBUSY; 224 } 225 226 wdd = watchdog; 227 228 err = misc_register(&watchdog_miscdev); 229 if (err != 0) { 230 pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n", 231 watchdog->info->identity, WATCHDOG_MINOR, err); 232 goto out; 233 } 234 235 return 0; 236 237 out: 238 wdd = NULL; 239 clear_bit(0, &watchdog_dev_busy); 240 return err; 241 } 242 243 /* 244 * watchdog_dev_unregister: 245 * @watchdog: watchdog device 246 * 247 * Deregister the /dev/watchdog device. 248 */ 249 250 int watchdog_dev_unregister(struct watchdog_device *watchdog) 251 { 252 /* Check that a watchdog device was registered in the past */ 253 if (!test_bit(0, &watchdog_dev_busy) || !wdd) 254 return -ENODEV; 255 256 /* We can only unregister the watchdog device that was registered */ 257 if (watchdog != wdd) { 258 pr_err("%s: watchdog was not registered as /dev/watchdog.\n", 259 watchdog->info->identity); 260 return -ENODEV; 261 } 262 263 misc_deregister(&watchdog_miscdev); 264 wdd = NULL; 265 clear_bit(0, &watchdog_dev_busy); 266 return 0; 267 } 268