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