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authorAndrew Dyer <amdyer@gmail.com>2008-01-08 15:40:37 -0500
committerWim Van Sebroeck <wim@iguana.be>2008-01-18 16:23:05 -0500
commit0d710cba3afde2109030254ee90654fbb580e8af (patch)
tree2a1f9a1b8462c7a2fa3cdece5fa3496b5fcd3e51 /Documentation
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')
-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 bb7cb1d31ec7..4cc4ba9d7150 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
42A more advanced driver could for example check that a HTTP server is 42A more advanced driver could for example check that a HTTP server is
43still responding before doing the write call to ping the watchdog. 43still responding before doing the write call to ping the watchdog.
44 44
45When the device is closed, the watchdog is disabled. This is not 45When the device is closed, the watchdog is disabled, unless the "Magic
46always such a good idea, since if there is a bug in the watchdog 46Close" feature is supported (see below). This is not always such a
47daemon and it crashes the system will not reboot. Because of this, 47good idea, since if there is a bug in the watchdog daemon and it
48some of the drivers support the configuration option "Disable watchdog 48crashes the system will not reboot. Because of this, some of the
49shutdown on close", CONFIG_WATCHDOG_NOWAYOUT. If it is set to Y when 49drivers support the configuration option "Disable watchdog shutdown on
50compiling the kernel, there is no way of disabling the watchdog once 50close", CONFIG_WATCHDOG_NOWAYOUT. If it is set to Y when compiling
51it has been started. So, if the watchdog daemon crashes, the system 51the kernel, there is no way of disabling the watchdog once it has been
52will reboot after the timeout has passed. Watchdog devices also usually 52started. So, if the watchdog daemon crashes, the system will reboot
53support the nowayout module parameter so that this option can be controlled 53after the timeout has passed. Watchdog devices also usually support
54at runtime. 54the nowayout module parameter so that this option can be controlled at
55 55runtime.
56Drivers will not disable the watchdog, unless a specific magic character 'V' 56
57has been sent /dev/watchdog just before closing the file. If the userspace 57Magic Close feature:
58daemon closes the file without sending this special character, the driver 58
59will assume that the daemon (and userspace in general) died, and will stop 59If a driver supports "Magic Close", the driver will not disable the
60pinging the watchdog without disabling it first. This will then cause a 60watchdog unless a specific magic character 'V' has been sent to
61reboot if the watchdog is not re-opened in sufficient time. 61/dev/watchdog just before closing the file. If the userspace daemon
62closes the file without sending this special character, the driver
63will assume that the daemon (and userspace in general) died, and will
64stop pinging the watchdog without disabling it first. This will then
65cause a reboot if the watchdog is not re-opened in sufficient time.
62 66
63The ioctl API: 67The ioctl API:
64 68