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authorAndrew Dyer <amdyer@gmail.com>2008-01-08 20:40:37 (GMT)
committerWim Van Sebroeck <wim@iguana.be>2008-01-18 21:23:05 (GMT)
commit0d710cba3afde2109030254ee90654fbb580e8af (patch)
tree2a1f9a1b8462c7a2fa3cdece5fa3496b5fcd3e51 /Documentation/watchdog
parentcde10ba3ba439592d1bc094102ebfccdeee80cf9 (diff)
[WATCHDOG] clarify watchdog operation in documentation
It was not clear what the difference is/was between the nowayout feature and the Magic Close feature. Signed-off-by: "Andrew Dyer" <amdyer@gmail.com> Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Diffstat (limited to 'Documentation/watchdog')
-rw-r--r--Documentation/watchdog/watchdog-api.txt38
1 files changed, 21 insertions, 17 deletions
diff --git a/Documentation/watchdog/watchdog-api.txt b/Documentation/watchdog/watchdog-api.txt
index bb7cb1d..4cc4ba9 100644
--- a/Documentation/watchdog/watchdog-api.txt
+++ b/Documentation/watchdog/watchdog-api.txt
@@ -42,23 +42,27 @@ 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.
-When the device is closed, the watchdog is disabled. 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.
-
-Drivers will not disable the watchdog, unless a specific magic character 'V'
-has been sent /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.
+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:

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