400 lines
12 KiB
Plaintext
400 lines
12 KiB
Plaintext
The Linux Watchdog driver API.
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Copyright 2002 Christer Weingel <wingel@nano-system.com>
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Some parts of this document are copied verbatim from the sbc60xxwdt
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driver which is (c) Copyright 2000 Jakob Oestergaard <jakob@ostenfeld.dk>
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This document describes the state of the Linux 2.4.18 kernel.
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Introduction:
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A Watchdog Timer (WDT) is a hardware circuit that can reset the
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computer system in case of a software fault. You probably knew that
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already.
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Usually a userspace daemon will notify the kernel watchdog driver via the
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/dev/watchdog special device file that userspace is still alive, at
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regular intervals. When such a notification occurs, the driver will
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usually tell the hardware watchdog that everything is in order, and
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that the watchdog should wait for yet another little while to reset
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the system. If userspace fails (RAM error, kernel bug, whatever), the
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notifications cease to occur, and the hardware watchdog will reset the
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system (causing a reboot) after the timeout occurs.
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The Linux watchdog API is a rather AD hoc construction and different
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drivers implement different, and sometimes incompatible, parts of it.
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This file is an attempt to document the existing usage and allow
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future driver writers to use it as a reference.
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The simplest API:
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All drivers support the basic mode of operation, where the watchdog
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activates as soon as /dev/watchdog is opened and will reboot unless
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the watchdog is pinged within a certain time, this time is called the
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timeout or margin. The simplest way to ping the watchdog is to write
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some data to the device. So a very simple watchdog daemon would look
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like this:
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int main(int argc, const char *argv[]) {
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int fd=open("/dev/watchdog",O_WRONLY);
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if (fd==-1) {
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perror("watchdog");
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exit(1);
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}
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while(1) {
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write(fd, "\0", 1);
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sleep(10);
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}
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}
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A more advanced driver could for example check that a HTTP server is
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still responding before doing the write call to ping the watchdog.
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When the device is closed, the watchdog is disabled. This is not
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always such a good idea, since if there is a bug in the watchdog
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daemon and it crashes the system will not reboot. Because of this,
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some of the drivers support the configuration option "Disable watchdog
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shutdown on close", CONFIG_WATCHDOG_NOWAYOUT. If it is set to Y when
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compiling the kernel, there is no way of disabling the watchdog once
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it has been started. So, if the watchdog dameon crashes, the system
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will reboot after the timeout has passed.
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Some other drivers will not disable the watchdog, unless a specific
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magic character 'V' has been sent /dev/watchdog just before closing
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the file. If the userspace daemon closes the file without sending
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this special character, the driver will assume that the daemon (and
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userspace in general) died, and will stop pinging the watchdog without
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disabling it first. This will then cause a reboot.
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The ioctl API:
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All conforming drivers also support an ioctl API.
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Pinging the watchdog using an ioctl:
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All drivers that have an ioctl interface support at least one ioctl,
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KEEPALIVE. This ioctl does exactly the same thing as a write to the
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watchdog device, so the main loop in the above program could be
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replaced with:
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while (1) {
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ioctl(fd, WDIOC_KEEPALIVE, 0);
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sleep(10);
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}
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the argument to the ioctl is ignored.
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Setting and getting the timeout:
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For some drivers it is possible to modify the watchdog timeout on the
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fly with the SETTIMEOUT ioctl, those drivers have the WDIOF_SETTIMEOUT
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flag set in their option field. The argument is an integer
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representing the timeout in seconds. The driver returns the real
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timeout used in the same variable, and this timeout might differ from
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the requested one due to limitation of the hardware.
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int timeout = 45;
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ioctl(fd, WDIOC_SETTIMEOUT, &timeout);
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printf("The timeout was set to %d seconds\n", timeout);
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This example might actually print "The timeout was set to 60 seconds"
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if the device has a granularity of minutes for its timeout.
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Starting with the Linux 2.4.18 kernel, it is possible to query the
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current timeout using the GETTIMEOUT ioctl.
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ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
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printf("The timeout was is %d seconds\n", timeout);
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Envinronmental monitoring:
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All watchdog drivers are required return more information about the system,
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some do temperature, fan and power level monitoring, some can tell you
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the reason for the last reboot of the system. The GETSUPPORT ioctl is
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available to ask what the device can do:
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struct watchdog_info ident;
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ioctl(fd, WDIOC_GETSUPPORT, &ident);
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the fields returned in the ident struct are:
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identity a string identifying the watchdog driver
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firmware_version the firmware version of the card if available
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options a flags describing what the device supports
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the options field can have the following bits set, and describes what
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kind of information that the GET_STATUS and GET_BOOT_STATUS ioctls can
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return. [FIXME -- Is this correct?]
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WDIOF_OVERHEAT Reset due to CPU overheat
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The machine was last rebooted by the watchdog because the thermal limit was
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exceeded
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WDIOF_FANFAULT Fan failed
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A system fan monitored by the watchdog card has failed
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WDIOF_EXTERN1 External relay 1
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External monitoring relay/source 1 was triggered. Controllers intended for
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real world applications include external monitoring pins that will trigger
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a reset.
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WDIOF_EXTERN2 External relay 2
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External monitoring relay/source 2 was triggered
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WDIOF_POWERUNDER Power bad/power fault
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The machine is showing an undervoltage status
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WDIOF_CARDRESET Card previously reset the CPU
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The last reboot was caused by the watchdog card
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WDIOF_POWEROVER Power over voltage
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The machine is showing an overvoltage status. Note that if one level is
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under and one over both bits will be set - this may seem odd but makes
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sense.
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WDIOF_KEEPALIVEPING Keep alive ping reply
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The watchdog saw a keepalive ping since it was last queried.
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WDIOF_SETTIMEOUT Can set/get the timeout
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For those drivers that return any bits set in the option field, the
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GETSTATUS and GETBOOTSTATUS ioctls can be used to ask for the current
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status, and the status at the last reboot, respectively.
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int flags;
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ioctl(fd, WDIOC_GETSTATUS, &flags);
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or
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ioctl(fd, WDIOC_GETBOOTSTATUS, &flags);
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Note that not all devices support these two calls, and some only
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support the GETBOOTSTATUS call.
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Some drivers can measure the temperature using the GETTEMP ioctl. The
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returned value is the temperature in degrees farenheit.
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int temperature;
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ioctl(fd, WDIOC_GETTEMP, &temperature);
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Finally the SETOPTIONS ioctl can be used to control some aspects of
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the cards operation; right now the pcwd driver is the only one
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supporting thiss ioctl.
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int options = 0;
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ioctl(fd, WDIOC_SETOPTIONS, options);
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The following options are available:
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WDIOS_DISABLECARD Turn off the watchdog timer
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WDIOS_ENABLECARD Turn on the watchdog timer
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WDIOS_TEMPPANIC Kernel panic on temperature trip
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[FIXME -- better explanations]
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Implementations in the current drivers in the kernel tree:
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Here I have tried to summarize what the different drivers support and
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where they do strange things compared to the other drivers.
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acquirewdt.c -- Acquire Single Board Computer
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This driver has a hardcoded timeout of 1 minute
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns KEEPALIVEPING. GETSTATUS will return 1 if
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the device is open, 0 if not. [FIXME -- isn't this rather
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silly? To be able to use the ioctl, the device must be open
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and so GETSTATUS will always return 1].
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advantechwdt.c -- Advantech Single Board Computer
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Timeout that defaults to 60 seconds, supports SETTIMEOUT.
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
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The GETSTATUS call returns if the device is open or not.
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[FIXME -- silliness again?]
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eurotechwdt.c -- Eurotech CPU-1220/1410
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The timeout can be set using the SETTIMEOUT ioctl and defaults
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to 60 seconds.
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Also has a module parameter "ev", event type which controls
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what should happen on a timeout, the string "int" or anything
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else that causes a reboot. [FIXME -- better description]
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns CARDRESET and WDIOF_SETTIMEOUT but
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GETSTATUS is not supported and GETBOOTSTATUS just returns 0.
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i810-tco.c -- Intel 810 chipset
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Also has support for a lot of other i8x0 stuff, but the
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watchdog is one of the things.
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The timeout is set using the module parameter "i810_margin",
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which is in steps of 0.6 seconds where 2<i810_margin<64. The
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driver supports the SETTIMEOUT ioctl.
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Supports CONFIG_WATCHDOG_NOWAYOUT.
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GETSUPPORT returns WDIOF_SETTIMEOUT. The GETSTATUS call
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returns some kind of timer value which ist not compatible with
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the other drivers. GETBOOT status returns some kind of
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hardware specific boot status. [FIXME -- describe this]
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ib700wdt.c -- IB700 Single Board Computer
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Default timeout of 30 seconds and the timeout is settable
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using the SETTIMEOUT ioctl. Note that only a few timeout
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values are supported.
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
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The GETSTATUS call returns if the device is open or not.
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[FIXME -- silliness again?]
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machzwd.c -- MachZ ZF-Logic
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Hardcoded timeout of 10 seconds
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Has a module parameter "action" that controls what happens
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when the timeout runs out which can be 0 = RESET (default),
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1 = SMI, 2 = NMI, 3 = SCI.
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Supports CONFIG_WATCHDOG_NOWAYOUT and the magic character
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'V' close handling.
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GETSUPPORT returns WDIOF_KEEPALIVEPING, and the GETSTATUS call
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returns if the device is open or not. [FIXME -- silliness
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again?]
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mixcomwd.c -- MixCom Watchdog
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[FIXME -- I'm unable to tell what the timeout is]
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns WDIOF_KEEPALIVEPING, GETSTATUS returns if
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the device is opened or not [FIXME -- I'm not really sure how
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this works, there seems to be some magic connected to
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CONFIG_WATCHDOG_NOWAYOUT]
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pcwd.c -- Berkshire PC Watchdog
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Hardcoded timeout of 1.5 seconds
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns WDIOF_OVERHEAT|WDIOF_CARDRESET and both
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GETSTATUS and GETBOOTSTATUS return something useful.
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The SETOPTIONS call can be used to enable and disable the card
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and to ask the driver to call panic if the system overheats.
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sbc60xxwdt.c -- 60xx Single Board Computer
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Hardcoded timeout of 10 seconds
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Does not support CONFIG_WATCHDOG_NOWAYOUT, but has the magic
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character 'V' close handling.
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No bits set in GETSUPPORT
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scx200.c -- National SCx200 CPUs
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Not in the kernel yet.
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The timeout is set using a module parameter "margin" which
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defaults to 60 seconds. The timeout can also be set using
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SETTIMEOUT and read using GETTIMEOUT.
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Supports a module parameter "nowayout" that is initialized
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with the value of CONFIG_WATCHDOG_NOWAYOUT. Also supports the
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magic character 'V' handling.
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shwdt.c -- SuperH 3/4 processors
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[FIXME -- I'm unable to tell what the timeout is]
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns WDIOF_KEEPALIVEPING, and the GETSTATUS call
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returns if the device is open or not. [FIXME -- silliness
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again?]
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softdog.c -- Software watchdog
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The timeout is set with the module parameter "soft_margin"
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which defaults to 60 seconds, the timeout is also settable
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using the SETTIMEOUT ioctl.
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Supports CONFIG_WATCHDOG_NOWAYOUT
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WDIOF_SETTIMEOUT bit set in GETSUPPORT
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w83877f_wdt.c -- W83877F Computer
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Hardcoded timeout of 30 seconds
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Does not support CONFIG_WATCHDOG_NOWAYOUT, but has the magic
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character 'V' close handling.
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No bits set in GETSUPPORT
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w83627hf_wdt.c -- w83627hf watchdog
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Timeout that defaults to 60 seconds, supports SETTIMEOUT.
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns WDIOF_KEEPALIVEPING and WDIOF_SETTIMEOUT.
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The GETSTATUS call returns if the device is open or not.
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wdt.c -- ICS WDT500/501 ISA and
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wdt_pci.c -- ICS WDT500/501 PCI
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Default timeout of 60 seconds. The timeout is also settable
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using the SETTIMEOUT ioctl.
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Supports CONFIG_WATCHDOG_NOWAYOUT
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GETSUPPORT returns with bits set depending on the actual
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card. The WDT501 supports a lot of external monitoring, the
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WDT500 much less.
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wdt285.c -- Footbridge watchdog
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The timeout is set with the module parameter "soft_margin"
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which defaults to 60 seconds. The timeout is also settable
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using the SETTIMEOUT ioctl.
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Does not support CONFIG_WATCHDOG_NOWAYOUT
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WDIOF_SETTIMEOUT bit set in GETSUPPORT
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wdt977.c -- Netwinder W83977AF chip
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Hardcoded timeout of 3 minutes
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Supports CONFIG_WATCHDOG_NOWAYOUT
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Does not support any ioctls at all.
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