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, &wddev->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, &wddev->status)) { 85 err = wddev->ops->start(wddev); 86 if (err < 0) 87 return err; 88 89 set_bit(WDOG_ACTIVE, &wddev->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 * If the 'nowayout' feature was set, the watchdog cannot be stopped. 102 */ 103 104 static int watchdog_stop(struct watchdog_device *wddev) 105 { 106 int err = -EBUSY; 107 108 if (test_bit(WDOG_NO_WAY_OUT, &wddev->status)) { 109 pr_info("%s: nowayout prevents watchdog to be stopped!\n", 110 wddev->info->identity); 111 return err; 112 } 113 114 if (test_bit(WDOG_ACTIVE, &wddev->status)) { 115 err = wddev->ops->stop(wddev); 116 if (err < 0) 117 return err; 118 119 clear_bit(WDOG_ACTIVE, &wddev->status); 120 } 121 return 0; 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. 132 * Writing the magic 'V' sequence allows the next close to turn 133 * off the watchdog (if 'nowayout' is not set). 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; 144 145 /* 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 */ 152 for (i = 0; i != len; i++) { 153 if (get_user(c, data + i)) 154 return -EFAULT; 155 if (c == 'V') 156 set_bit(WDOG_ALLOW_RELEASE, &wdd->status); 157 } 158 159 /* someone wrote to us, so we send the watchdog a keepalive ping */ 160 watchdog_ping(wdd); 161 162 return len; 163 } 164 165 /* 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; 181 int err; 182 183 if (wdd->ops->ioctl) { 184 err = wdd->ops->ioctl(wdd, cmd, arg); 185 if (err != -ENOIOCTLCMD) 186 return err; 187 } 188 189 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); 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; 212 case WDIOC_KEEPALIVE: 213 if (!(wdd->info->options & WDIOF_KEEPALIVEPING)) 214 return -EOPNOTSUPP; 215 watchdog_ping(wdd); 216 return 0; 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; 223 if ((wdd->max_timeout != 0) && 224 (val < wdd->min_timeout || val > wdd->max_timeout)) 225 return -EINVAL; 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); 240 default: 241 return -ENOTTY; 242 } 243 } 244 245 /* 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; 269 270 err = watchdog_start(wdd); 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 * 289 * This is the code for when /dev/watchdog gets closed. We will only 290 * stop the watchdog when we have received the magic char (and nowayout 291 * was not set), else the watchdog will keep running. 292 */ 293 294 static int watchdog_release(struct inode *inode, struct file *file) 295 { 296 int err = -EBUSY; 297 298 /* 299 * We only stop the watchdog if we received the magic character 300 * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then 301 * watchdog_stop will fail. 302 */ 303 if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) || 304 !(wdd->info->options & WDIOF_MAGICCLOSE)) 305 err = watchdog_stop(wdd); 306 307 /* If the watchdog was not stopped, send a keepalive ping */ 308 if (err < 0) { 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, 325 .unlocked_ioctl = watchdog_ioctl, 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)) { 350 pr_err("only one watchdog can use /dev/watchdog\n"); 351 return -EBUSY; 352 } 353 354 wdd = watchdog; 355 356 err = misc_register(&watchdog_miscdev); 357 if (err != 0) { 358 pr_err("%s: cannot register miscdev on minor=%d (err=%d)\n", 359 watchdog->info->identity, WATCHDOG_MINOR, err); 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) { 386 pr_err("%s: watchdog was not registered as /dev/watchdog\n", 387 watchdog->info->identity); 388 return -ENODEV; 389 } 390 391 misc_deregister(&watchdog_miscdev); 392 wdd = NULL; 393 clear_bit(0, &watchdog_dev_busy); 394 return 0; 395 } 396