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 /* If the watchdog is active then we send a keepalive ping 230 * to make sure that the watchdog keep's running (and if 231 * possible that it takes the new timeout) */ 232 watchdog_ping(wdd); 233 /* Fall */ 234 case WDIOC_GETTIMEOUT: 235 /* timeout == 0 means that we don't know the timeout */ 236 if (wdd->timeout == 0) 237 return -EOPNOTSUPP; 238 return put_user(wdd->timeout, p); 239 case WDIOC_GETTIMELEFT: 240 if (!wdd->ops->get_timeleft) 241 return -EOPNOTSUPP; 242 243 return put_user(wdd->ops->get_timeleft(wdd), p); 244 default: 245 return -ENOTTY; 246 } 247 } 248 249 /* 250 * watchdog_open: open the /dev/watchdog device. 251 * @inode: inode of device 252 * @file: file handle to device 253 * 254 * When the /dev/watchdog device gets opened, we start the watchdog. 255 * Watch out: the /dev/watchdog device is single open, so we make sure 256 * it can only be opened once. 257 */ 258 259 static int watchdog_open(struct inode *inode, struct file *file) 260 { 261 int err = -EBUSY; 262 263 /* the watchdog is single open! */ 264 if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status)) 265 return -EBUSY; 266 267 /* 268 * If the /dev/watchdog device is open, we don't want the module 269 * to be unloaded. 270 */ 271 if (!try_module_get(wdd->ops->owner)) 272 goto out; 273 274 err = watchdog_start(wdd); 275 if (err < 0) 276 goto out_mod; 277 278 /* dev/watchdog is a virtual (and thus non-seekable) filesystem */ 279 return nonseekable_open(inode, file); 280 281 out_mod: 282 module_put(wdd->ops->owner); 283 out: 284 clear_bit(WDOG_DEV_OPEN, &wdd->status); 285 return err; 286 } 287 288 /* 289 * watchdog_release: release the /dev/watchdog device. 290 * @inode: inode of device 291 * @file: file handle to device 292 * 293 * This is the code for when /dev/watchdog gets closed. We will only 294 * stop the watchdog when we have received the magic char (and nowayout 295 * was not set), else the watchdog will keep running. 296 */ 297 298 static int watchdog_release(struct inode *inode, struct file *file) 299 { 300 int err = -EBUSY; 301 302 /* 303 * We only stop the watchdog if we received the magic character 304 * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then 305 * watchdog_stop will fail. 306 */ 307 if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) || 308 !(wdd->info->options & WDIOF_MAGICCLOSE)) 309 err = watchdog_stop(wdd); 310 311 /* If the watchdog was not stopped, send a keepalive ping */ 312 if (err < 0) { 313 pr_crit("%s: watchdog did not stop!\n", wdd->info->identity); 314 watchdog_ping(wdd); 315 } 316 317 /* Allow the owner module to be unloaded again */ 318 module_put(wdd->ops->owner); 319 320 /* make sure that /dev/watchdog can be re-opened */ 321 clear_bit(WDOG_DEV_OPEN, &wdd->status); 322 323 return 0; 324 } 325 326 static const struct file_operations watchdog_fops = { 327 .owner = THIS_MODULE, 328 .write = watchdog_write, 329 .unlocked_ioctl = watchdog_ioctl, 330 .open = watchdog_open, 331 .release = watchdog_release, 332 }; 333 334 static struct miscdevice watchdog_miscdev = { 335 .minor = WATCHDOG_MINOR, 336 .name = "watchdog", 337 .fops = &watchdog_fops, 338 }; 339 340 /* 341 * watchdog_dev_register: 342 * @watchdog: watchdog device 343 * 344 * Register a watchdog device as /dev/watchdog. /dev/watchdog 345 * is actually a miscdevice and thus we set it up like that. 346 */ 347 348 int watchdog_dev_register(struct watchdog_device *watchdog) 349 { 350 int err; 351 352 /* Only one device can register for /dev/watchdog */ 353 if (test_and_set_bit(0, &watchdog_dev_busy)) { 354 pr_err("only one watchdog can use /dev/watchdog\n"); 355 return -EBUSY; 356 } 357 358 wdd = watchdog; 359 360 err = misc_register(&watchdog_miscdev); 361 if (err != 0) { 362 pr_err("%s: cannot register miscdev on minor=%d (err=%d)\n", 363 watchdog->info->identity, WATCHDOG_MINOR, err); 364 goto out; 365 } 366 367 return 0; 368 369 out: 370 wdd = NULL; 371 clear_bit(0, &watchdog_dev_busy); 372 return err; 373 } 374 375 /* 376 * watchdog_dev_unregister: 377 * @watchdog: watchdog device 378 * 379 * Deregister the /dev/watchdog device. 380 */ 381 382 int watchdog_dev_unregister(struct watchdog_device *watchdog) 383 { 384 /* Check that a watchdog device was registered in the past */ 385 if (!test_bit(0, &watchdog_dev_busy) || !wdd) 386 return -ENODEV; 387 388 /* We can only unregister the watchdog device that was registered */ 389 if (watchdog != wdd) { 390 pr_err("%s: watchdog was not registered as /dev/watchdog\n", 391 watchdog->info->identity); 392 return -ENODEV; 393 } 394 395 misc_deregister(&watchdog_miscdev); 396 wdd = NULL; 397 clear_bit(0, &watchdog_dev_busy); 398 return 0; 399 } 400