fedora core 6 1.2949 + vserver 2.2.0

[linux-2.6.git] / Documentation / watchdog / watchdog-api.txt

diff --git a/Documentation/watchdog/watchdog-api.txt b/Documentation/watchdog/watchdog-api.txt
index c5beb54..8d16f6f 100644 (file)
--- a/Documentation/watchdog/watchdog-api.txt
+++ b/Documentation/watchdog/watchdog-api.txt
@@ -34,19 +34,7 @@ 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:
-
-int main(int argc, const char *argv[]) {
-       int fd=open("/dev/watchdog",O_WRONLY);
-       if (fd==-1) {
-               perror("watchdog");
-               exit(1);
-       }
-       while(1) {
-               write(fd, "\0", 1);
-               sleep(10);
-       }
-}
+like this source file:  see Documentation/watchdog/src/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.
@@ -57,7 +45,7 @@ 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 dameon crashes, the system
+it has been started.  So, if the watchdog daemon crashes, the system
 will reboot after the timeout has passed.
 
 Some other drivers will not disable the watchdog, unless a specific
@@ -107,7 +95,40 @@ current timeout using the GETTIMEOUT ioctl.
     ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
     printf("The timeout was is %d seconds\n", timeout);
 
-Envinronmental monitoring:
+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 pretimout will go of 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
@@ -166,6 +187,10 @@ 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
@@ -182,14 +207,14 @@ 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 farenheit.
+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; right now the pcwd driver is the only one
-supporting thiss ioctl.
+supporting this ioctl.
 
     int options = 0;
     ioctl(fd, WDIOC_SETOPTIONS, options);
@@ -233,13 +258,13 @@ booke_wdt.c -- PowerPC BookE Watchdog Timer
        Timeout default varies according to frequency, supports
        SETTIMEOUT
 
-       Watchdog can not be turned off, CONFIG_WATCHDOG_NOWAYOUT
+       Watchdog cannot be turned off, CONFIG_WATCHDOG_NOWAYOUT
        does not make sense
 
        GETSUPPORT returns the watchdog_info struct, and
        GETSTATUS returns the supported options. GETBOOTSTATUS
        returns a 1 if the last reset was caused by the
-       watchdog and a 0 otherwise. This watchdog can not be
+       watchdog and a 0 otherwise. This watchdog cannot be
        disabled once it has been started. The wdt_period kernel
        parameter selects which bit of the time base changing
        from 0->1 will trigger the watchdog exception. Changing