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-rw-r--r--Documentation/watchdog/watchdog-api.txt56
1 files changed, 39 insertions, 17 deletions
diff --git a/Documentation/watchdog/watchdog-api.txt b/Documentation/watchdog/watchdog-api.txt
index 21ed5117366..958ff3d48be 100644
--- a/Documentation/watchdog/watchdog-api.txt
+++ b/Documentation/watchdog/watchdog-api.txt
@@ -34,22 +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:
-
-#include <stdlib.h>
-#include <fcntl.h>
-
-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.
@@ -110,7 +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
@@ -169,6 +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