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The watchdog framework takes care of feeding a hardware watchdog until userspace opens /dev/watchdogN. If that never happens for some reason (buggy init script, corrupt root filesystem or whatnot) but the kernel itself is fine, the machine stays up indefinitely. This patch allows setting an upper limit for how long the kernel will take care of the watchdog, thus ensuring that the watchdog will eventually reset the machine. A value of 0 (the default) means infinite timeout, preserving the current behaviour. This is particularly useful for embedded devices where some fallback logic is implemented in the bootloader (e.g., use a different root partition, boot from network, ...). There is already handle_boot_enabled serving a similar purpose. However, such a binary choice is unsuitable if the hardware watchdog cannot be programmed by the bootloader to provide a timeout long enough for userspace to get up and running. Many of the embedded devices we see use external (gpio-triggered) watchdogs with a fixed timeout of the order of 1-2 seconds. The open timeout only applies for the first open from userspace. Should userspace need to close the watchdog device, with the intention of re-opening it shortly, the application can emulate the open timeout feature by combining the nowayout feature with an appropriate WDIOC_SETTIMEOUT immediately prior to closing the device. Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk> Reviewed-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.