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| -rw-r--r-- | Documentation/watchdog/watchdog-api.rst (renamed from Documentation/watchdog/watchdog-api.txt) | 76 |
1 files changed, 55 insertions, 21 deletions
diff --git a/Documentation/watchdog/watchdog-api.txt b/Documentation/watchdog/watchdog-api.rst index 0e62ba33b7fb..c6c1e9fa9f73 100644 --- a/Documentation/watchdog/watchdog-api.txt +++ b/Documentation/watchdog/watchdog-api.rst @@ -1,7 +1,10 @@ +============================= +The Linux Watchdog driver API +============================= + Last reviewed: 10/05/2007 -The Linux Watchdog driver API. Copyright 2002 Christer Weingel <wingel@nano-system.com> @@ -10,7 +13,8 @@ driver which is (c) Copyright 2000 Jakob Oestergaard <jakob@ostenfeld.dk> This document describes the state of the Linux 2.4.18 kernel. -Introduction: +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 @@ -30,7 +34,8 @@ 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: +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 @@ -54,7 +59,8 @@ 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: +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 @@ -64,7 +70,8 @@ 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: +The ioctl API +============= All conforming drivers also support an ioctl API. @@ -73,7 +80,7 @@ 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: +replaced with:: while (1) { ioctl(fd, WDIOC_KEEPALIVE, 0); @@ -82,14 +89,15 @@ replaced with: the argument to the ioctl is ignored. -Setting and getting the timeout: +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. +the requested one due to limitation of the hardware:: int timeout = 45; ioctl(fd, WDIOC_SETTIMEOUT, &timeout); @@ -99,18 +107,19 @@ 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. +current timeout using the GETTIMEOUT ioctl:: ioctl(fd, WDIOC_GETTIMEOUT, &timeout); printf("The timeout was is %d seconds\n", timeout); -Pretimeouts: +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. +resets:: pretimeout = 10; ioctl(fd, WDIOC_SETPRETIMEOUT, &pretimeout); @@ -121,89 +130,113 @@ 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: +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: +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. +that returns the number of seconds before reboot:: ioctl(fd, WDIOC_GETTIMELEFT, &timeleft); printf("The timeout was is %d seconds\n", timeleft); -Environmental monitoring: +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: +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 +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. +status, and the status at the last reboot, respectively:: int flags; ioctl(fd, WDIOC_GETSTATUS, &flags); @@ -216,22 +249,23 @@ 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. +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. +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] - |