Documentation/watchdog/watchdog-api.txt

   1 The Linux Watchdog driver API.
   2
   3 Copyright 2002 Christer Weingel <wingel@nano-system.com>
   4
   5 Some parts of this document are copied verbatim from the sbc60xxwdt
   6 driver which is (c) Copyright 2000 Jakob Oestergaard <jakob@ostenfeld.dk>
   7
   8 This document describes the state of the Linux 2.4.18 kernel.
   9
  10 Introduction:
  11
  12 A Watchdog Timer (WDT) is a hardware circuit that can reset the
  13 computer system in case of a software fault.  You probably knew that
  14 already.
  15
  16 Usually a userspace daemon will notify the kernel watchdog driver via the
  17 /dev/watchdog special device file that userspace is still alive, at
  18 regular intervals.  When such a notification occurs, the driver will
  19 usually tell the hardware watchdog that everything is in order, and
  20 that the watchdog should wait for yet another little while to reset
  21 the system.  If userspace fails (RAM error, kernel bug, whatever), the
  22 notifications cease to occur, and the hardware watchdog will reset the
  23 system (causing a reboot) after the timeout occurs.
  24
  25 The Linux watchdog API is a rather AD hoc construction and different
  26 drivers implement different, and sometimes incompatible, parts of it.
  27 This file is an attempt to document the existing usage and allow
  28 future driver writers to use it as a reference.
  29
  30 The simplest API:
  31
  32 All drivers support the basic mode of operation, where the watchdog
  33 activates as soon as /dev/watchdog is opened and will reboot unless
  34 the watchdog is pinged within a certain time, this time is called the
  35 timeout or margin.  The simplest way to ping the watchdog is to write
  36 some data to the device.  So a very simple watchdog daemon would look
  37 like this:
  38
  39 #include <stdlib.h>
  40 #include <fcntl.h>
  41
  42 int main(int argc, const char *argv[]) {
  43         int fd=open("/dev/watchdog",O_WRONLY);
  44         if (fd==-1) {
  45                 perror("watchdog");
  46                 exit(1);
  47         }
  48         while(1) {
  49                 write(fd, "\0", 1);
  50                 sleep(10);
  51         }
  52 }
  53
  54 A more advanced driver could for example check that a HTTP server is
  55 still responding before doing the write call to ping the watchdog.
  56
  57 When the device is closed, the watchdog is disabled.  This is not
  58 always such a good idea, since if there is a bug in the watchdog
  59 daemon and it crashes the system will not reboot.  Because of this,
  60 some of the drivers support the configuration option "Disable watchdog
  61 shutdown on close", CONFIG_WATCHDOG_NOWAYOUT.  If it is set to Y when
  62 compiling the kernel, there is no way of disabling the watchdog once
  63 it has been started.  So, if the watchdog dameon crashes, the system
  64 will reboot after the timeout has passed.
  65
  66 Some other drivers will not disable the watchdog, unless a specific
  67 magic character 'V' has been sent /dev/watchdog just before closing
  68 the file.  If the userspace daemon closes the file without sending
  69 this special character, the driver will assume that the daemon (and
  70 userspace in general) died, and will stop pinging the watchdog without
  71 disabling it first.  This will then cause a reboot.
  72
  73 The ioctl API:
  74
  75 All conforming drivers also support an ioctl API.
  76
  77 Pinging the watchdog using an ioctl:
  78
  79 All drivers that have an ioctl interface support at least one ioctl,
  80 KEEPALIVE.  This ioctl does exactly the same thing as a write to the
  81 watchdog device, so the main loop in the above program could be
  82 replaced with:
  83
  84         while (1) {
  85                 ioctl(fd, WDIOC_KEEPALIVE, 0);
  86                 sleep(10);
  87         }
  88
  89 the argument to the ioctl is ignored.
  90
  91 Setting and getting the timeout:
  92
  93 For some drivers it is possible to modify the watchdog timeout on the
  94 fly with the SETTIMEOUT ioctl, those drivers have the WDIOF_SETTIMEOUT
  95 flag set in their option field.  The argument is an integer
  96 representing the timeout in seconds.  The driver returns the real
  97 timeout used in the same variable, and this timeout might differ from
  98 the requested one due to limitation of the hardware.
  99
 100     int timeout = 45;
 101     ioctl(fd, WDIOC_SETTIMEOUT, &timeout);
 102     printf("The timeout was set to %d seconds\n", timeout);
 103
 104 This example might actually print "The timeout was set to 60 seconds"
 105 if the device has a granularity of minutes for its timeout.
 106
 107 Starting with the Linux 2.4.18 kernel, it is possible to query the
 108 current timeout using the GETTIMEOUT ioctl.
 109
 110     ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
 111     printf("The timeout was is %d seconds\n", timeout);
 112
 113 Envinronmental monitoring:
 114
 115 All watchdog drivers are required return more information about the system,
 116 some do temperature, fan and power level monitoring, some can tell you
 117 the reason for the last reboot of the system.  The GETSUPPORT ioctl is
 118 available to ask what the device can do:
 119
 120         struct watchdog_info ident;
 121         ioctl(fd, WDIOC_GETSUPPORT, &ident);
 122
 123 the fields returned in the ident struct are:
 124
 125         identity                a string identifying the watchdog driver
 126         firmware_version        the firmware version of the card if available
 127         options                 a flags describing what the device supports
 128
 129 the options field can have the following bits set, and describes what
 130 kind of information that the GET_STATUS and GET_BOOT_STATUS ioctls can
 131 return.   [FIXME -- Is this correct?]
 132
 133         WDIOF_OVERHEAT          Reset due to CPU overheat
 134
 135 The machine was last rebooted by the watchdog because the thermal limit was
 136 exceeded
 137
 138         WDIOF_FANFAULT          Fan failed
 139
 140 A system fan monitored by the watchdog card has failed
 141
 142         WDIOF_EXTERN1           External relay 1
 143
 144 External monitoring relay/source 1 was triggered. Controllers intended for
 145 real world applications include external monitoring pins that will trigger
 146 a reset.
 147
 148         WDIOF_EXTERN2           External relay 2
 149
 150 External monitoring relay/source 2 was triggered
 151
 152         WDIOF_POWERUNDER        Power bad/power fault
 153
 154 The machine is showing an undervoltage status
 155
 156         WDIOF_CARDRESET         Card previously reset the CPU
 157
 158 The last reboot was caused by the watchdog card
 159
 160         WDIOF_POWEROVER         Power over voltage
 161
 162 The machine is showing an overvoltage status. Note that if one level is
 163 under and one over both bits will be set - this may seem odd but makes
 164 sense.
 165
 166         WDIOF_KEEPALIVEPING     Keep alive ping reply
 167
 168 The watchdog saw a keepalive ping since it was last queried.
 169
 170         WDIOF_SETTIMEOUT        Can set/get the timeout
 171
 172
 173 For those drivers that return any bits set in the option field, the
 174 GETSTATUS and GETBOOTSTATUS ioctls can be used to ask for the current
 175 status, and the status at the last reboot, respectively.
 176
 177     int flags;
 178     ioctl(fd, WDIOC_GETSTATUS, &flags);
 179
 180     or
 181
 182     ioctl(fd, WDIOC_GETBOOTSTATUS, &flags);
 183
 184 Note that not all devices support these two calls, and some only
 185 support the GETBOOTSTATUS call.
 186
 187 Some drivers can measure the temperature using the GETTEMP ioctl.  The
 188 returned value is the temperature in degrees farenheit.
 189
 190     int temperature;
 191     ioctl(fd, WDIOC_GETTEMP, &temperature);
 192
 193 Finally the SETOPTIONS ioctl can be used to control some aspects of
 194 the cards operation; right now the pcwd driver is the only one
 195 supporting thiss ioctl.
 196
 197     int options = 0;
 198     ioctl(fd, WDIOC_SETOPTIONS, options);
 199
 200 The following options are available:
 201
 202         WDIOS_DISABLECARD       Turn off the watchdog timer
 203         WDIOS_ENABLECARD        Turn on the watchdog timer
 204         WDIOS_TEMPPANIC         Kernel panic on temperature trip
 205
 206 [FIXME -- better explanations]
 207
 208 Implementations in the current drivers in the kernel tree:
 209
 210 Here I have tried to summarize what the different drivers support and
 211 where they do strange things compared to the other drivers.
 212
 213 acquirewdt.c -- Acquire Single Board Computer
 214
 215         This driver has a hardcoded timeout of 1 minute
 216
 217         Supports CONFIG_WATCHDOG_NOWAYOUT
 218
 219         GETSUPPORT returns KEEPALIVEPING.  GETSTATUS will return 1 if
 220         the device is open, 0 if not.  [FIXME -- isn't this rather
 221         silly?  To be able to use the ioctl, the device must be open
 222         and so GETSTATUS will always return 1].
 223
 224 advantechwdt.c -- Advantech Single Board Computer
 225
 226         Timeout that defaults to 60 seconds, supports SETTIMEOUT.
 227
 228         Supports CONFIG_WATCHDOG_NOWAYOUT
 229
 230         GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
 231         The GETSTATUS call returns if the device is open or not.
 232         [FIXME -- silliness again?]
 233
 234 booke_wdt.c -- PowerPC BookE Watchdog Timer
 235
 236         Timeout default varies according to frequency, supports
 237         SETTIMEOUT
 238
 239         Watchdog can not be turned off, CONFIG_WATCHDOG_NOWAYOUT
 240         does not make sense
 241
 242         GETSUPPORT returns the watchdog_info struct, and
 243         GETSTATUS returns the supported options. GETBOOTSTATUS
 244         returns a 1 if the last reset was caused by the
 245         watchdog and a 0 otherwise. This watchdog can not be
 246         disabled once it has been started. The wdt_period kernel
 247         parameter selects which bit of the time base changing
 248         from 0->1 will trigger the watchdog exception. Changing
 249         the timeout from the ioctl calls will change the
 250         wdt_period as defined above. Finally if you would like to
 251         replace the default Watchdog Handler you can implement the
 252         WatchdogHandler() function in your own code.
 253
 254 eurotechwdt.c -- Eurotech CPU-1220/1410
 255
 256         The timeout can be set using the SETTIMEOUT ioctl and defaults
 257         to 60 seconds.
 258
 259         Also has a module parameter "ev", event type which controls
 260         what should happen on a timeout, the string "int" or anything
 261         else that causes a reboot.  [FIXME -- better description]
 262
 263         Supports CONFIG_WATCHDOG_NOWAYOUT
 264
 265         GETSUPPORT returns CARDRESET and WDIOF_SETTIMEOUT but
 266         GETSTATUS is not supported and GETBOOTSTATUS just returns 0.
 267
 268 i810-tco.c -- Intel 810 chipset
 269
 270         Also has support for a lot of other i8x0 stuff, but the
 271         watchdog is one of the things.
 272
 273         The timeout is set using the module parameter "i810_margin",
 274         which is in steps of 0.6 seconds where 2<i810_margin<64.  The
 275         driver supports the SETTIMEOUT ioctl.
 276
 277         Supports CONFIG_WATCHDOG_NOWAYOUT.
 278
 279         GETSUPPORT returns WDIOF_SETTIMEOUT.  The GETSTATUS call
 280         returns some kind of timer value which ist not compatible with
 281         the other drivers.  GETBOOT status returns some kind of
 282         hardware specific boot status.  [FIXME -- describe this]
 283
 284 ib700wdt.c -- IB700 Single Board Computer
 285
 286         Default timeout of 30 seconds and the timeout is settable
 287         using the SETTIMEOUT ioctl.  Note that only a few timeout
 288         values are supported.
 289
 290         Supports CONFIG_WATCHDOG_NOWAYOUT
 291
 292         GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
 293         The GETSTATUS call returns if the device is open or not.
 294         [FIXME -- silliness again?]
 295
 296 machzwd.c -- MachZ ZF-Logic
 297
 298         Hardcoded timeout of 10 seconds
 299
 300         Has a module parameter "action" that controls what happens
 301         when the timeout runs out which can be 0 = RESET (default),
 302         1 = SMI, 2 = NMI, 3 = SCI.
 303
 304         Supports CONFIG_WATCHDOG_NOWAYOUT and the magic character
 305         'V' close handling.
 306
 307         GETSUPPORT returns WDIOF_KEEPALIVEPING, and the GETSTATUS call
 308         returns if the device is open or not.  [FIXME -- silliness
 309         again?]
 310
 311 mixcomwd.c -- MixCom Watchdog
 312
 313         [FIXME -- I'm unable to tell what the timeout is]
 314
 315         Supports CONFIG_WATCHDOG_NOWAYOUT
 316
 317         GETSUPPORT returns WDIOF_KEEPALIVEPING, GETSTATUS returns if
 318         the device is opened or not [FIXME -- I'm not really sure how
 319         this works, there seems to be some magic connected to
 320         CONFIG_WATCHDOG_NOWAYOUT]
 321
 322 pcwd.c -- Berkshire PC Watchdog
 323
 324         Hardcoded timeout of 1.5 seconds
 325
 326         Supports CONFIG_WATCHDOG_NOWAYOUT
 327
 328         GETSUPPORT returns WDIOF_OVERHEAT|WDIOF_CARDRESET and both
 329         GETSTATUS and GETBOOTSTATUS return something useful.
 330
 331         The SETOPTIONS call can be used to enable and disable the card
 332         and to ask the driver to call panic if the system overheats.
 333
 334 sbc60xxwdt.c -- 60xx Single Board Computer
 335
 336         Hardcoded timeout of 10 seconds
 337
 338         Does not support CONFIG_WATCHDOG_NOWAYOUT, but has the magic
 339         character 'V' close handling.
 340
 341         No bits set in GETSUPPORT
 342
 343 scx200.c -- National SCx200 CPUs
 344
 345         Not in the kernel yet.
 346
 347         The timeout is set using a module parameter "margin" which
 348         defaults to 60 seconds.  The timeout can also be set using
 349         SETTIMEOUT and read using GETTIMEOUT.
 350
 351         Supports a module parameter "nowayout" that is initialized
 352         with the value of CONFIG_WATCHDOG_NOWAYOUT.  Also supports the
 353         magic character 'V' handling.
 354
 355 shwdt.c -- SuperH 3/4 processors
 356
 357         [FIXME -- I'm unable to tell what the timeout is]
 358
 359         Supports CONFIG_WATCHDOG_NOWAYOUT
 360
 361         GETSUPPORT returns WDIOF_KEEPALIVEPING, and the GETSTATUS call
 362         returns if the device is open or not.  [FIXME -- silliness
 363         again?]
 364
 365 softdog.c -- Software watchdog
 366
 367         The timeout is set with the module parameter "soft_margin"
 368         which defaults to 60 seconds, the timeout is also settable
 369         using the SETTIMEOUT ioctl.
 370
 371         Supports CONFIG_WATCHDOG_NOWAYOUT
 372
 373         WDIOF_SETTIMEOUT bit set in GETSUPPORT
 374
 375 w83877f_wdt.c -- W83877F Computer
 376
 377         Hardcoded timeout of 30 seconds
 378
 379         Does not support CONFIG_WATCHDOG_NOWAYOUT, but has the magic
 380         character 'V' close handling.
 381
 382         No bits set in GETSUPPORT
 383
 384 w83627hf_wdt.c -- w83627hf watchdog
 385
 386         Timeout that defaults to 60 seconds, supports SETTIMEOUT.
 387
 388         Supports CONFIG_WATCHDOG_NOWAYOUT
 389
 390         GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
 391         The GETSTATUS call returns if the device is open or not.
 392
 393 wdt.c -- ICS WDT500/501 ISA and
 394 wdt_pci.c -- ICS WDT500/501 PCI
 395
 396         Default timeout of 60 seconds.  The timeout is also settable
 397         using the SETTIMEOUT ioctl.
 398
 399         Supports CONFIG_WATCHDOG_NOWAYOUT
 400
 401         GETSUPPORT returns with bits set depending on the actual
 402         card. The WDT501 supports a lot of external monitoring, the
 403         WDT500 much less.
 404
 405 wdt285.c -- Footbridge watchdog
 406
 407         The timeout is set with the module parameter "soft_margin"
 408         which defaults to 60 seconds.  The timeout is also settable
 409         using the SETTIMEOUT ioctl.
 410
 411         Does not support CONFIG_WATCHDOG_NOWAYOUT
 412
 413         WDIOF_SETTIMEOUT bit set in GETSUPPORT
 414
 415 wdt977.c -- Netwinder W83977AF chip
 416
 417         Hardcoded timeout of 3 minutes
 418
 419         Supports CONFIG_WATCHDOG_NOWAYOUT
 420
 421         Does not support any ioctls at all.
 422