drivers/watchdog/watchdog_dev.c

   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 }