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 source file:  see Documentation/watchdog/src/watchdog-simple.c
  38
  39 A more advanced driver could for example check that a HTTP server is
  40 still responding before doing the write call to ping the watchdog.
  41
  42 When the device is closed, the watchdog is disabled.  This is not
  43 always such a good idea, since if there is a bug in the watchdog
  44 daemon and it crashes the system will not reboot.  Because of this,
  45 some of the drivers support the configuration option "Disable watchdog
  46 shutdown on close", CONFIG_WATCHDOG_NOWAYOUT.  If it is set to Y when
  47 compiling the kernel, there is no way of disabling the watchdog once
  48 it has been started.  So, if the watchdog dameon crashes, the system
  49 will reboot after the timeout has passed.
  50
  51 Some other drivers will not disable the watchdog, unless a specific
  52 magic character 'V' has been sent /dev/watchdog just before closing
  53 the file.  If the userspace daemon closes the file without sending
  54 this special character, the driver will assume that the daemon (and
  55 userspace in general) died, and will stop pinging the watchdog without
  56 disabling it first.  This will then cause a reboot.
  57
  58 The ioctl API:
  59
  60 All conforming drivers also support an ioctl API.
  61
  62 Pinging the watchdog using an ioctl:
  63
  64 All drivers that have an ioctl interface support at least one ioctl,
  65 KEEPALIVE.  This ioctl does exactly the same thing as a write to the
  66 watchdog device, so the main loop in the above program could be
  67 replaced with:
  68
  69         while (1) {
  70                 ioctl(fd, WDIOC_KEEPALIVE, 0);
  71                 sleep(10);
  72         }
  73
  74 the argument to the ioctl is ignored.
  75
  76 Setting and getting the timeout:
  77
  78 For some drivers it is possible to modify the watchdog timeout on the
  79 fly with the SETTIMEOUT ioctl, those drivers have the WDIOF_SETTIMEOUT
  80 flag set in their option field.  The argument is an integer
  81 representing the timeout in seconds.  The driver returns the real
  82 timeout used in the same variable, and this timeout might differ from
  83 the requested one due to limitation of the hardware.
  84
  85     int timeout = 45;
  86     ioctl(fd, WDIOC_SETTIMEOUT, &timeout);
  87     printf("The timeout was set to %d seconds\n", timeout);
  88
  89 This example might actually print "The timeout was set to 60 seconds"
  90 if the device has a granularity of minutes for its timeout.
  91
  92 Starting with the Linux 2.4.18 kernel, it is possible to query the
  93 current timeout using the GETTIMEOUT ioctl.
  94
  95     ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
  96     printf("The timeout was is %d seconds\n", timeout);
  97
  98 Pretimeouts:
  99
 100 Some watchdog timers can be set to have a trigger go off before the
 101 actual time they will reset the system.  This can be done with an NMI,
 102 interrupt, or other mechanism.  This allows Linux to record useful
 103 information (like panic information and kernel coredumps) before it
 104 resets.
 105
 106     pretimeout = 10;
 107     ioctl(fd, WDIOC_SETPRETIMEOUT, &pretimeout);
 108
 109 Note that the pretimeout is the number of seconds before the time
 110 when the timeout will go off.  It is not the number of seconds until
 111 the pretimeout.  So, for instance, if you set the timeout to 60 seconds
 112 and the pretimeout to 10 seconds, the pretimout will go of in 50
 113 seconds.  Setting a pretimeout to zero disables it.
 114
 115 There is also a get function for getting the pretimeout:
 116
 117     ioctl(fd, WDIOC_GETPRETIMEOUT, &timeout);
 118     printf("The pretimeout was is %d seconds\n", timeout);
 119
 120 Not all watchdog drivers will support a pretimeout.
 121
 122 Get the number of seconds before reboot:
 123
 124 Some watchdog drivers have the ability to report the remaining time
 125 before the system will reboot. The WDIOC_GETTIMELEFT is the ioctl
 126 that returns the number of seconds before reboot.
 127
 128     ioctl(fd, WDIOC_GETTIMELEFT, &timeleft);
 129     printf("The timeout was is %d seconds\n", timeleft);
 130
 131 Environmental monitoring:
 132
 133 All watchdog drivers are required return more information about the system,
 134 some do temperature, fan and power level monitoring, some can tell you
 135 the reason for the last reboot of the system.  The GETSUPPORT ioctl is
 136 available to ask what the device can do:
 137
 138         struct watchdog_info ident;
 139         ioctl(fd, WDIOC_GETSUPPORT, &ident);
 140
 141 the fields returned in the ident struct are:
 142
 143         identity                a string identifying the watchdog driver
 144         firmware_version        the firmware version of the card if available
 145         options                 a flags describing what the device supports
 146
 147 the options field can have the following bits set, and describes what
 148 kind of information that the GET_STATUS and GET_BOOT_STATUS ioctls can
 149 return.   [FIXME -- Is this correct?]
 150
 151         WDIOF_OVERHEAT          Reset due to CPU overheat
 152
 153 The machine was last rebooted by the watchdog because the thermal limit was
 154 exceeded
 155
 156         WDIOF_FANFAULT          Fan failed
 157
 158 A system fan monitored by the watchdog card has failed
 159
 160         WDIOF_EXTERN1           External relay 1
 161
 162 External monitoring relay/source 1 was triggered. Controllers intended for
 163 real world applications include external monitoring pins that will trigger
 164 a reset.
 165
 166         WDIOF_EXTERN2           External relay 2
 167
 168 External monitoring relay/source 2 was triggered
 169
 170         WDIOF_POWERUNDER        Power bad/power fault
 171
 172 The machine is showing an undervoltage status
 173
 174         WDIOF_CARDRESET         Card previously reset the CPU
 175
 176 The last reboot was caused by the watchdog card
 177
 178         WDIOF_POWEROVER         Power over voltage
 179
 180 The machine is showing an overvoltage status. Note that if one level is
 181 under and one over both bits will be set - this may seem odd but makes
 182 sense.
 183
 184         WDIOF_KEEPALIVEPING     Keep alive ping reply
 185
 186 The watchdog saw a keepalive ping since it was last queried.
 187
 188         WDIOF_SETTIMEOUT        Can set/get the timeout
 189
 190 The watchdog can do pretimeouts.
 191
 192         WDIOF_PRETIMEOUT        Pretimeout (in seconds), get/set
 193
 194
 195 For those drivers that return any bits set in the option field, the
 196 GETSTATUS and GETBOOTSTATUS ioctls can be used to ask for the current
 197 status, and the status at the last reboot, respectively.
 198
 199     int flags;
 200     ioctl(fd, WDIOC_GETSTATUS, &flags);
 201
 202     or
 203
 204     ioctl(fd, WDIOC_GETBOOTSTATUS, &flags);
 205
 206 Note that not all devices support these two calls, and some only
 207 support the GETBOOTSTATUS call.
 208
 209 Some drivers can measure the temperature using the GETTEMP ioctl.  The
 210 returned value is the temperature in degrees farenheit.
 211
 212     int temperature;
 213     ioctl(fd, WDIOC_GETTEMP, &temperature);
 214
 215 Finally the SETOPTIONS ioctl can be used to control some aspects of
 216 the cards operation; right now the pcwd driver is the only one
 217 supporting thiss ioctl.
 218
 219     int options = 0;
 220     ioctl(fd, WDIOC_SETOPTIONS, options);
 221
 222 The following options are available:
 223
 224         WDIOS_DISABLECARD       Turn off the watchdog timer
 225         WDIOS_ENABLECARD        Turn on the watchdog timer
 226         WDIOS_TEMPPANIC         Kernel panic on temperature trip
 227
 228 [FIXME -- better explanations]
 229
 230 Implementations in the current drivers in the kernel tree:
 231
 232 Here I have tried to summarize what the different drivers support and
 233 where they do strange things compared to the other drivers.
 234
 235 acquirewdt.c -- Acquire Single Board Computer
 236
 237         This driver has a hardcoded timeout of 1 minute
 238
 239         Supports CONFIG_WATCHDOG_NOWAYOUT
 240
 241         GETSUPPORT returns KEEPALIVEPING.  GETSTATUS will return 1 if
 242         the device is open, 0 if not.  [FIXME -- isn't this rather
 243         silly?  To be able to use the ioctl, the device must be open
 244         and so GETSTATUS will always return 1].
 245
 246 advantechwdt.c -- Advantech Single Board Computer
 247
 248         Timeout that defaults to 60 seconds, supports SETTIMEOUT.
 249
 250         Supports CONFIG_WATCHDOG_NOWAYOUT
 251
 252         GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
 253         The GETSTATUS call returns if the device is open or not.
 254         [FIXME -- silliness again?]
 255
 256 booke_wdt.c -- PowerPC BookE Watchdog Timer
 257
 258         Timeout default varies according to frequency, supports
 259         SETTIMEOUT
 260
 261         Watchdog can not be turned off, CONFIG_WATCHDOG_NOWAYOUT
 262         does not make sense
 263
 264         GETSUPPORT returns the watchdog_info struct, and
 265         GETSTATUS returns the supported options. GETBOOTSTATUS
 266         returns a 1 if the last reset was caused by the
 267         watchdog and a 0 otherwise. This watchdog can not be
 268         disabled once it has been started. The wdt_period kernel
 269         parameter selects which bit of the time base changing
 270         from 0->1 will trigger the watchdog exception. Changing
 271         the timeout from the ioctl calls will change the
 272         wdt_period as defined above. Finally if you would like to
 273         replace the default Watchdog Handler you can implement the
 274         WatchdogHandler() function in your own code.
 275
 276 eurotechwdt.c -- Eurotech CPU-1220/1410
 277
 278         The timeout can be set using the SETTIMEOUT ioctl and defaults
 279         to 60 seconds.
 280
 281         Also has a module parameter "ev", event type which controls
 282         what should happen on a timeout, the string "int" or anything
 283         else that causes a reboot.  [FIXME -- better description]
 284
 285         Supports CONFIG_WATCHDOG_NOWAYOUT
 286
 287         GETSUPPORT returns CARDRESET and WDIOF_SETTIMEOUT but
 288         GETSTATUS is not supported and GETBOOTSTATUS just returns 0.
 289
 290 i810-tco.c -- Intel 810 chipset
 291
 292         Also has support for a lot of other i8x0 stuff, but the
 293         watchdog is one of the things.
 294
 295         The timeout is set using the module parameter "i810_margin",
 296         which is in steps of 0.6 seconds where 2<i810_margin<64.  The
 297         driver supports the SETTIMEOUT ioctl.
 298
 299         Supports CONFIG_WATCHDOG_NOWAYOUT.
 300
 301         GETSUPPORT returns WDIOF_SETTIMEOUT.  The GETSTATUS call
 302         returns some kind of timer value which ist not compatible with
 303         the other drivers.  GETBOOT status returns some kind of
 304         hardware specific boot status.  [FIXME -- describe this]
 305
 306 ib700wdt.c -- IB700 Single Board Computer
 307
 308         Default timeout of 30 seconds and the timeout is settable
 309         using the SETTIMEOUT ioctl.  Note that only a few timeout
 310         values are supported.
 311
 312         Supports CONFIG_WATCHDOG_NOWAYOUT
 313
 314         GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
 315         The GETSTATUS call returns if the device is open or not.
 316         [FIXME -- silliness again?]
 317
 318 machzwd.c -- MachZ ZF-Logic
 319
 320         Hardcoded timeout of 10 seconds
 321
 322         Has a module parameter "action" that controls what happens
 323         when the timeout runs out which can be 0 = RESET (default),
 324         1 = SMI, 2 = NMI, 3 = SCI.
 325
 326         Supports CONFIG_WATCHDOG_NOWAYOUT and the magic character
 327         'V' close handling.
 328
 329         GETSUPPORT returns WDIOF_KEEPALIVEPING, and the GETSTATUS call
 330         returns if the device is open or not.  [FIXME -- silliness
 331         again?]
 332
 333 mixcomwd.c -- MixCom Watchdog
 334
 335         [FIXME -- I'm unable to tell what the timeout is]
 336
 337         Supports CONFIG_WATCHDOG_NOWAYOUT
 338
 339         GETSUPPORT returns WDIOF_KEEPALIVEPING, GETSTATUS returns if
 340         the device is opened or not [FIXME -- I'm not really sure how
 341         this works, there seems to be some magic connected to
 342         CONFIG_WATCHDOG_NOWAYOUT]
 343
 344 pcwd.c -- Berkshire PC Watchdog
 345
 346         Hardcoded timeout of 1.5 seconds
 347
 348         Supports CONFIG_WATCHDOG_NOWAYOUT
 349
 350         GETSUPPORT returns WDIOF_OVERHEAT|WDIOF_CARDRESET and both
 351         GETSTATUS and GETBOOTSTATUS return something useful.
 352
 353         The SETOPTIONS call can be used to enable and disable the card
 354         and to ask the driver to call panic if the system overheats.
 355
 356 sbc60xxwdt.c -- 60xx Single Board Computer
 357
 358         Hardcoded timeout of 10 seconds
 359
 360         Does not support CONFIG_WATCHDOG_NOWAYOUT, but has the magic
 361         character 'V' close handling.
 362
 363         No bits set in GETSUPPORT
 364
 365 scx200.c -- National SCx200 CPUs
 366
 367         Not in the kernel yet.
 368
 369         The timeout is set using a module parameter "margin" which
 370         defaults to 60 seconds.  The timeout can also be set using
 371         SETTIMEOUT and read using GETTIMEOUT.
 372
 373         Supports a module parameter "nowayout" that is initialized
 374         with the value of CONFIG_WATCHDOG_NOWAYOUT.  Also supports the
 375         magic character 'V' handling.
 376
 377 shwdt.c -- SuperH 3/4 processors
 378
 379         [FIXME -- I'm unable to tell what the timeout is]
 380
 381         Supports CONFIG_WATCHDOG_NOWAYOUT
 382
 383         GETSUPPORT returns WDIOF_KEEPALIVEPING, and the GETSTATUS call
 384         returns if the device is open or not.  [FIXME -- silliness
 385         again?]
 386
 387 softdog.c -- Software watchdog
 388
 389         The timeout is set with the module parameter "soft_margin"
 390         which defaults to 60 seconds, the timeout is also settable
 391         using the SETTIMEOUT ioctl.
 392
 393         Supports CONFIG_WATCHDOG_NOWAYOUT
 394
 395         WDIOF_SETTIMEOUT bit set in GETSUPPORT
 396
 397 w83877f_wdt.c -- W83877F Computer
 398
 399         Hardcoded timeout of 30 seconds
 400
 401         Does not support CONFIG_WATCHDOG_NOWAYOUT, but has the magic
 402         character 'V' close handling.
 403
 404         No bits set in GETSUPPORT
 405
 406 w83627hf_wdt.c -- w83627hf watchdog
 407
 408         Timeout that defaults to 60 seconds, supports SETTIMEOUT.
 409
 410         Supports CONFIG_WATCHDOG_NOWAYOUT
 411
 412         GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
 413         The GETSTATUS call returns if the device is open or not.
 414
 415 wdt.c -- ICS WDT500/501 ISA and
 416 wdt_pci.c -- ICS WDT500/501 PCI
 417
 418         Default timeout of 60 seconds.  The timeout is also settable
 419         using the SETTIMEOUT ioctl.
 420
 421         Supports CONFIG_WATCHDOG_NOWAYOUT
 422
 423         GETSUPPORT returns with bits set depending on the actual
 424         card. The WDT501 supports a lot of external monitoring, the
 425         WDT500 much less.
 426
 427 wdt285.c -- Footbridge watchdog
 428
 429         The timeout is set with the module parameter "soft_margin"
 430         which defaults to 60 seconds.  The timeout is also settable
 431         using the SETTIMEOUT ioctl.
 432
 433         Does not support CONFIG_WATCHDOG_NOWAYOUT
 434
 435         WDIOF_SETTIMEOUT bit set in GETSUPPORT
 436
 437 wdt977.c -- Netwinder W83977AF chip
 438
 439         Hardcoded timeout of 3 minutes
 440
 441         Supports CONFIG_WATCHDOG_NOWAYOUT
 442
 443         Does not support any ioctls at all.
 444