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diff --git a/Documentation/watchdog/watchdog-api.txt b/Documentation/watchdog/watchdog-api.txt deleted file mode 100644 index 0e62ba33b7fb..000000000000 --- a/Documentation/watchdog/watchdog-api.txt +++ /dev/null @@ -1,237 +0,0 @@ -Last reviewed: 10/05/2007 - - -The Linux Watchdog driver API. - -Copyright 2002 Christer Weingel <wingel@nano-system.com> - -Some parts of this document are copied verbatim from the sbc60xxwdt -driver which is (c) Copyright 2000 Jakob Oestergaard <jakob@ostenfeld.dk> - -This document describes the state of the Linux 2.4.18 kernel. - -Introduction: - -A Watchdog Timer (WDT) is a hardware circuit that can reset the -computer system in case of a software fault. You probably knew that -already. - -Usually a userspace daemon will notify the kernel watchdog driver via the -/dev/watchdog special device file that userspace is still alive, at -regular intervals. When such a notification occurs, the driver will -usually tell the hardware watchdog that everything is in order, and -that the watchdog should wait for yet another little while to reset -the system. If userspace fails (RAM error, kernel bug, whatever), the -notifications cease to occur, and the hardware watchdog will reset the -system (causing a reboot) after the timeout occurs. - -The Linux watchdog API is a rather ad-hoc construction and different -drivers implement different, and sometimes incompatible, parts of it. -This file is an attempt to document the existing usage and allow -future driver writers to use it as a reference. - -The simplest API: - -All drivers support the basic mode of operation, where the watchdog -activates as soon as /dev/watchdog is opened and will reboot unless -the watchdog is pinged within a certain time, this time is called the -timeout or margin. The simplest way to ping the watchdog is to write -some data to the device. So a very simple watchdog daemon would look -like this source file: see samples/watchdog/watchdog-simple.c - -A more advanced driver could for example check that a HTTP server is -still responding before doing the write call to ping the watchdog. - -When the device is closed, the watchdog is disabled, unless the "Magic -Close" feature is supported (see below). This is not always such a -good idea, since if there is a bug in the watchdog daemon and it -crashes the system will not reboot. Because of this, some of the -drivers support the configuration option "Disable watchdog shutdown on -close", CONFIG_WATCHDOG_NOWAYOUT. If it is set to Y when compiling -the kernel, there is no way of disabling the watchdog once it has been -started. So, if the watchdog daemon crashes, the system will reboot -after the timeout has passed. Watchdog devices also usually support -the nowayout module parameter so that this option can be controlled at -runtime. - -Magic Close feature: - -If a driver supports "Magic Close", the driver will not disable the -watchdog unless a specific magic character 'V' has been sent to -/dev/watchdog just before closing the file. If the userspace daemon -closes the file without sending this special character, the driver -will assume that the daemon (and userspace in general) died, and will -stop pinging the watchdog without disabling it first. This will then -cause a reboot if the watchdog is not re-opened in sufficient time. - -The ioctl API: - -All conforming drivers also support an ioctl API. - -Pinging the watchdog using an ioctl: - -All drivers that have an ioctl interface support at least one ioctl, -KEEPALIVE. This ioctl does exactly the same thing as a write to the -watchdog device, so the main loop in the above program could be -replaced with: - - while (1) { - ioctl(fd, WDIOC_KEEPALIVE, 0); - sleep(10); - } - -the argument to the ioctl is ignored. - -Setting and getting the timeout: - -For some drivers it is possible to modify the watchdog timeout on the -fly with the SETTIMEOUT ioctl, those drivers have the WDIOF_SETTIMEOUT -flag set in their option field. The argument is an integer -representing the timeout in seconds. The driver returns the real -timeout used in the same variable, and this timeout might differ from -the requested one due to limitation of the hardware. - - int timeout = 45; - ioctl(fd, WDIOC_SETTIMEOUT, &timeout); - printf("The timeout was set to %d seconds\n", timeout); - -This example might actually print "The timeout was set to 60 seconds" -if the device has a granularity of minutes for its timeout. - -Starting with the Linux 2.4.18 kernel, it is possible to query the -current timeout using the GETTIMEOUT ioctl. - - ioctl(fd, WDIOC_GETTIMEOUT, &timeout); - printf("The timeout was is %d seconds\n", timeout); - -Pretimeouts: - -Some watchdog timers can be set to have a trigger go off before the -actual time they will reset the system. This can be done with an NMI, -interrupt, or other mechanism. This allows Linux to record useful -information (like panic information and kernel coredumps) before it -resets. - - pretimeout = 10; - ioctl(fd, WDIOC_SETPRETIMEOUT, &pretimeout); - -Note that the pretimeout is the number of seconds before the time -when the timeout will go off. It is not the number of seconds until -the pretimeout. So, for instance, if you set the timeout to 60 seconds -and the pretimeout to 10 seconds, the pretimeout will go off in 50 -seconds. Setting a pretimeout to zero disables it. - -There is also a get function for getting the pretimeout: - - ioctl(fd, WDIOC_GETPRETIMEOUT, &timeout); - printf("The pretimeout was is %d seconds\n", timeout); - -Not all watchdog drivers will support a pretimeout. - -Get the number of seconds before reboot: - -Some watchdog drivers have the ability to report the remaining time -before the system will reboot. The WDIOC_GETTIMELEFT is the ioctl -that returns the number of seconds before reboot. - - ioctl(fd, WDIOC_GETTIMELEFT, &timeleft); - printf("The timeout was is %d seconds\n", timeleft); - -Environmental monitoring: - -All watchdog drivers are required return more information about the system, -some do temperature, fan and power level monitoring, some can tell you -the reason for the last reboot of the system. The GETSUPPORT ioctl is -available to ask what the device can do: - - struct watchdog_info ident; - ioctl(fd, WDIOC_GETSUPPORT, &ident); - -the fields returned in the ident struct are: - - identity a string identifying the watchdog driver - firmware_version the firmware version of the card if available - options a flags describing what the device supports - -the options field can have the following bits set, and describes what -kind of information that the GET_STATUS and GET_BOOT_STATUS ioctls can -return. [FIXME -- Is this correct?] - - WDIOF_OVERHEAT Reset due to CPU overheat - -The machine was last rebooted by the watchdog because the thermal limit was -exceeded - - WDIOF_FANFAULT Fan failed - -A system fan monitored by the watchdog card has failed - - WDIOF_EXTERN1 External relay 1 - -External monitoring relay/source 1 was triggered. Controllers intended for -real world applications include external monitoring pins that will trigger -a reset. - - WDIOF_EXTERN2 External relay 2 - -External monitoring relay/source 2 was triggered - - WDIOF_POWERUNDER Power bad/power fault - -The machine is showing an undervoltage status - - WDIOF_CARDRESET Card previously reset the CPU - -The last reboot was caused by the watchdog card - - WDIOF_POWEROVER Power over voltage - -The machine is showing an overvoltage status. Note that if one level is -under and one over both bits will be set - this may seem odd but makes -sense. - - WDIOF_KEEPALIVEPING Keep alive ping reply - -The watchdog saw a keepalive ping since it was last queried. - - WDIOF_SETTIMEOUT Can set/get the timeout - -The watchdog can do pretimeouts. - - WDIOF_PRETIMEOUT Pretimeout (in seconds), get/set - - -For those drivers that return any bits set in the option field, the -GETSTATUS and GETBOOTSTATUS ioctls can be used to ask for the current -status, and the status at the last reboot, respectively. - - int flags; - ioctl(fd, WDIOC_GETSTATUS, &flags); - - or - - ioctl(fd, WDIOC_GETBOOTSTATUS, &flags); - -Note that not all devices support these two calls, and some only -support the GETBOOTSTATUS call. - -Some drivers can measure the temperature using the GETTEMP ioctl. The -returned value is the temperature in degrees fahrenheit. - - int temperature; - ioctl(fd, WDIOC_GETTEMP, &temperature); - -Finally the SETOPTIONS ioctl can be used to control some aspects of -the cards operation. - - int options = 0; - ioctl(fd, WDIOC_SETOPTIONS, &options); - -The following options are available: - - WDIOS_DISABLECARD Turn off the watchdog timer - WDIOS_ENABLECARD Turn on the watchdog timer - WDIOS_TEMPPANIC Kernel panic on temperature trip - -[FIXME -- better explanations] - |