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 * We only ping when the watchdog device is running. 58 */ 59 60 static int watchdog_ping(struct watchdog_device *wddev) 61 { 62 if (test_bit(WDOG_ACTIVE, &wdd->status)) { 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 84 if (!test_bit(WDOG_ACTIVE, &wdd->status)) { 85 err = wddev->ops->start(wddev); 86 if (err < 0) 87 return err; 88 89 set_bit(WDOG_ACTIVE, &wdd->status); 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. 101 */ 102 103 static int watchdog_stop(struct watchdog_device *wddev) 104 { 105 int err; 106 107 if (test_bit(WDOG_ACTIVE, &wdd->status)) { 108 err = wddev->ops->stop(wddev); 109 if (err < 0) 110 return err; 111 112 clear_bit(WDOG_ACTIVE, &wdd->status); 113 } 114 return 0; 115 } 116 117 /* 118 * watchdog_write: writes to the watchdog. 119 * @file: file from VFS 120 * @data: user address of data 121 * @len: length of data 122 * @ppos: pointer to the file offset 123 * 124 * A write to a watchdog device is defined as a keepalive ping. 125 */ 126 127 static ssize_t watchdog_write(struct file *file, const char __user *data, 128 size_t len, loff_t *ppos) 129 { 130 size_t i; 131 char c; 132 133 if (len == 0) 134 return 0; 135 136 for (i = 0; i != len; i++) { 137 if (get_user(c, data + i)) 138 return -EFAULT; 139 } 140 141 /* someone wrote to us, so we send the watchdog a keepalive ping */ 142 watchdog_ping(wdd); 143 144 return len; 145 } 146 147 /* 148 * watchdog_ioctl: handle the different ioctl's for the watchdog device. 149 * @file: file handle to the device 150 * @cmd: watchdog command 151 * @arg: argument pointer 152 * 153 * The watchdog API defines a common set of functions for all watchdogs 154 * according to their available features. 155 */ 156 157 static long watchdog_ioctl(struct file *file, unsigned int cmd, 158 unsigned long arg) 159 { 160 void __user *argp = (void __user *)arg; 161 int __user *p = argp; 162 unsigned int val; 163 int err; 164 165 switch (cmd) { 166 case WDIOC_GETSUPPORT: 167 return copy_to_user(argp, wdd->info, 168 sizeof(struct watchdog_info)) ? -EFAULT : 0; 169 case WDIOC_GETSTATUS: 170 val = wdd->ops->status ? wdd->ops->status(wdd) : 0; 171 return put_user(val, p); 172 case WDIOC_GETBOOTSTATUS: 173 return put_user(wdd->bootstatus, p); 174 case WDIOC_SETOPTIONS: 175 if (get_user(val, p)) 176 return -EFAULT; 177 if (val & WDIOS_DISABLECARD) { 178 err = watchdog_stop(wdd); 179 if (err < 0) 180 return err; 181 } 182 if (val & WDIOS_ENABLECARD) { 183 err = watchdog_start(wdd); 184 if (err < 0) 185 return err; 186 } 187 return 0; 188 case WDIOC_KEEPALIVE: 189 if (!(wdd->info->options & WDIOF_KEEPALIVEPING)) 190 return -EOPNOTSUPP; 191 watchdog_ping(wdd); 192 return 0; 193 default: 194 return -ENOTTY; 195 } 196 } 197 198 /* 199 * watchdog_open: open the /dev/watchdog device. 200 * @inode: inode of device 201 * @file: file handle to device 202 * 203 * When the /dev/watchdog device gets opened, we start the watchdog. 204 * Watch out: the /dev/watchdog device is single open, so we make sure 205 * it can only be opened once. 206 */ 207 208 static int watchdog_open(struct inode *inode, struct file *file) 209 { 210 int err = -EBUSY; 211 212 /* the watchdog is single open! */ 213 if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status)) 214 return -EBUSY; 215 216 /* 217 * If the /dev/watchdog device is open, we don't want the module 218 * to be unloaded. 219 */ 220 if (!try_module_get(wdd->ops->owner)) 221 goto out; 222 223 err = watchdog_start(wdd); 224 if (err < 0) 225 goto out_mod; 226 227 /* dev/watchdog is a virtual (and thus non-seekable) filesystem */ 228 return nonseekable_open(inode, file); 229 230 out_mod: 231 module_put(wdd->ops->owner); 232 out: 233 clear_bit(WDOG_DEV_OPEN, &wdd->status); 234 return err; 235 } 236 237 /* 238 * watchdog_release: release the /dev/watchdog device. 239 * @inode: inode of device 240 * @file: file handle to device 241 * 242 * This is the code for when /dev/watchdog gets closed. 243 */ 244 245 static int watchdog_release(struct inode *inode, struct file *file) 246 { 247 int err; 248 249 err = watchdog_stop(wdd); 250 if (err < 0) { 251 pr_crit("%s: watchdog did not stop!\n", wdd->info->identity); 252 watchdog_ping(wdd); 253 } 254 255 /* Allow the owner module to be unloaded again */ 256 module_put(wdd->ops->owner); 257 258 /* make sure that /dev/watchdog can be re-opened */ 259 clear_bit(WDOG_DEV_OPEN, &wdd->status); 260 261 return 0; 262 } 263 264 static const struct file_operations watchdog_fops = { 265 .owner = THIS_MODULE, 266 .write = watchdog_write, 267 .unlocked_ioctl = watchdog_ioctl, 268 .open = watchdog_open, 269 .release = watchdog_release, 270 }; 271 272 static struct miscdevice watchdog_miscdev = { 273 .minor = WATCHDOG_MINOR, 274 .name = "watchdog", 275 .fops = &watchdog_fops, 276 }; 277 278 /* 279 * watchdog_dev_register: 280 * @watchdog: watchdog device 281 * 282 * Register a watchdog device as /dev/watchdog. /dev/watchdog 283 * is actually a miscdevice and thus we set it up like that. 284 */ 285 286 int watchdog_dev_register(struct watchdog_device *watchdog) 287 { 288 int err; 289 290 /* Only one device can register for /dev/watchdog */ 291 if (test_and_set_bit(0, &watchdog_dev_busy)) { 292 pr_err("only one watchdog can use /dev/watchdog.\n"); 293 return -EBUSY; 294 } 295 296 wdd = watchdog; 297 298 err = misc_register(&watchdog_miscdev); 299 if (err != 0) { 300 pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n", 301 watchdog->info->identity, WATCHDOG_MINOR, err); 302 goto out; 303 } 304 305 return 0; 306 307 out: 308 wdd = NULL; 309 clear_bit(0, &watchdog_dev_busy); 310 return err; 311 } 312 313 /* 314 * watchdog_dev_unregister: 315 * @watchdog: watchdog device 316 * 317 * Deregister the /dev/watchdog device. 318 */ 319 320 int watchdog_dev_unregister(struct watchdog_device *watchdog) 321 { 322 /* Check that a watchdog device was registered in the past */ 323 if (!test_bit(0, &watchdog_dev_busy) || !wdd) 324 return -ENODEV; 325 326 /* We can only unregister the watchdog device that was registered */ 327 if (watchdog != wdd) { 328 pr_err("%s: watchdog was not registered as /dev/watchdog.\n", 329 watchdog->info->identity); 330 return -ENODEV; 331 } 332 333 misc_deregister(&watchdog_miscdev); 334 wdd = NULL; 335 clear_bit(0, &watchdog_dev_busy); 336 return 0; 337 } 338