[PATCH v5] Documentation: Refactored watchdog old doc

[PATCH v5] Documentation: Refactored watchdog old doc

[Sunny Patel]

Mark WDIOC_GETTEMP and WDIOS_TEMPPANIC as deprecated since
neither is implemented by the watchdog core and both are only
present in a small number of legacy drivers.

Add documentation for previously undocumented status bits
WDIOF_MAGICCLOSE and WDIOF_ALARMONLY in the options field.

Add documentation for WDIOF_PRETIMEOUT and WDIOF_SETTIMEOUT
status bits describing their respective ioctls.

Fix the following issues in existing documentation:
  - Remove version-specific reference to Linux 2.4.18 from
    the GETTIMEOUT ioctl description
  - Fix duplicate "was is" in printf format strings
  - Replace [FIXME] placeholder with proper descriptions for
    WDIOS_DISABLECARD, WDIOS_ENABLECARD and WDIOS_TEMPPANIC

Signed-off-by: Sunny Patel <nueralspacetech@gmail.com>
---

Changes in v5:
  - Fixed WDIOC_GETTIMELEFT printf statement to correctly reference 
    "timeleft" instead of "timeout".
  
Changes in v4:
  - Fixed WDIOS_DISABLECARD description: corrected inverted logic —
    the ioctl disables the hardware timer entirely rather than
    stopping pings. Clarified that userspace, not the kernel driver,
    is primarily responsible for pinging under normal operation.

 Documentation/watchdog/watchdog-api.rst | 65 +++++++++++++++++++++----
 1 file changed, 55 insertions(+), 10 deletions(-)

diff --git a/Documentation/watchdog/watchdog-api.rst b/Documentation/watchdog/watchdog-api.rst
index 78e228c272cf..736436a68f65 100644
--- a/Documentation/watchdog/watchdog-api.rst
+++ b/Documentation/watchdog/watchdog-api.rst
@@ -2,7 +2,7 @@
 The Linux Watchdog driver API
 =============================
 
-Last reviewed: 10/05/2007
+Last reviewed: 04/08/2026
 
 
 
@@ -42,7 +42,7 @@ 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 source file:  see samples/watchdog/watchdog-simple.c
+like this source file: see samples/watchdog/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.
@@ -106,11 +106,10 @@ the requested one due to limitation of the hardware::
 This example might actually print "The timeout was set to 60 seconds"
 if the device has a granularity of minutes for its timeout.
 
-Starting with the Linux 2.4.18 kernel, it is possible to query the
-current timeout using the GETTIMEOUT ioctl::
+It is also possible to get the current timeout with the GETTIMEOUT ioctl::
 
     ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
-    printf("The timeout was is %d seconds\n", timeout);
+    printf("The timeout is %d seconds\n", timeout);
 
 Pretimeouts
 ===========
@@ -133,7 +132,7 @@ 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);
+    printf("The pretimeout is %d seconds\n", timeout);
 
 Not all watchdog drivers will support a pretimeout.
 
@@ -145,12 +144,12 @@ 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);
+    printf("The timeleft is %d seconds\n", timeleft);
 
 Environmental monitoring
 ========================
 
-All watchdog drivers are required return more information about the system,
+All watchdog drivers are required to return more information about the system,
 some do temperature, fan and power level monitoring, some can tell you
 the reason for the last reboot of the system.  The GETSUPPORT ioctl is
 available to ask what the device can do::
@@ -227,12 +226,33 @@ The watchdog saw a keepalive ping since it was last queried.
 	WDIOF_SETTIMEOUT	Can set/get the timeout
 	================	=======================
 
-The watchdog can do pretimeouts.
+The watchdog supports timeout set/get via the WDIOC_SETTIMEOUT and
+WDIOC_GETTIMEOUT ioctls.
 
 	================	================================
 	WDIOF_PRETIMEOUT	Pretimeout (in seconds), get/set
 	================	================================
 
+The watchdog supports a pretimeout, a warning interrupt that fires before
+the actual reboot timeout. Use WDIOC_SETPRETIMEOUT and WDIOC_GETPRETIMEOUT
+to set/get the pretimeout.
+
+	================	================================
+	WDIOF_MAGICCLOSE	Supports magic close char
+	================	================================
+
+The driver supports the Magic Close feature. The watchdog is only disabled
+if the character 'V' is written to /dev/watchdog before the file descriptor
+is closed. Without writing 'V' before closing, the watchdog remains active
+and will trigger a reboot after the timeout expires.
+
+	================	================================
+	WDIOF_ALARMONLY		Not a reboot watchdog
+	================	================================
+
+The watchdog will not reboot the system when it expires. Instead it
+triggers a management or other external alarm. Userspace should not
+rely on a system reboot occurring.
 
 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
@@ -254,6 +274,11 @@ returned value is the temperature in degrees Fahrenheit::
     int temperature;
     ioctl(fd, WDIOC_GETTEMP, &temperature);
 
+.. note::
+	``WDIOC_GETTEMP`` is not implemented by the watchdog core and is
+	considered deprecated. It is only supported by a small number of
+	legacy drivers. New drivers should not implement it.
+
 Finally the SETOPTIONS ioctl can be used to control some aspects of
 the cards operation::
 
@@ -268,4 +293,24 @@ The following options are available:
 	WDIOS_TEMPPANIC		Kernel panic on temperature trip
 	=================	================================
 
-[FIXME -- better explanations]
+``WDIOS_DISABLECARD`` disables the hardware watchdog timer entirely,
+allowing a controlled system shutdown without triggering a reboot.
+Userspace is responsible for pinging the watchdog under normal
+operation; this ioctl stops the underlying hardware timer so that
+the absence of pings no longer causes a system reset.
+
+``WDIOS_ENABLECARD`` starts the watchdog timer. If the watchdog was
+previously stopped via ``WDIOS_DISABLECARD``, this will re-enable it. The
+hardware watchdog will begin counting down from the configured timeout.
+
+``WDIOS_TEMPPANIC`` enables temperature-based kernel panic. When set,
+the driver will call ``panic()`` (or ``kernel_power_off()`` on some
+drivers) if the hardware temperature sensor exceeds its threshold,
+rather than only setting the ``WDIOF_OVERHEAT`` status bit. Support
+for this option is driver-specific; not all watchdog drivers implement
+temperature monitoring.
+
+.. note::
+	``WDIOS_TEMPPANIC`` is not implemented by the watchdog core and is
+	considered deprecated. It is only present in a small number of
+	legacy drivers. New drivers should not implement it.
-- 
2.43.0

Re: [PATCH v5] Documentation: Refactored watchdog old doc

[Guenter Roeck]

On 4/12/26 21:11, Sunny Patel wrote:
> Mark WDIOC_GETTEMP and WDIOS_TEMPPANIC as deprecated since
> neither is implemented by the watchdog core and both are only
> present in a small number of legacy drivers.
> 
> Add documentation for previously undocumented status bits
> WDIOF_MAGICCLOSE and WDIOF_ALARMONLY in the options field.
> 
> Add documentation for WDIOF_PRETIMEOUT and WDIOF_SETTIMEOUT
> status bits describing their respective ioctls.
> 
> Fix the following issues in existing documentation:
>    - Remove version-specific reference to Linux 2.4.18 from
>      the GETTIMEOUT ioctl description
>    - Fix duplicate "was is" in printf format strings
>    - Replace [FIXME] placeholder with proper descriptions for
>      WDIOS_DISABLECARD, WDIOS_ENABLECARD and WDIOS_TEMPPANIC
> 
> Signed-off-by: Sunny Patel <nueralspacetech@gmail.com>

Reviewed-by: Guenter Roeck <linux@ropeck-us.net>

> ---
> 
> Changes in v5:
>    - Fixed WDIOC_GETTIMELEFT printf statement to correctly reference
>      "timeleft" instead of "timeout".
>    
> Changes in v4:
>    - Fixed WDIOS_DISABLECARD description: corrected inverted logic —
>      the ioctl disables the hardware timer entirely rather than
>      stopping pings. Clarified that userspace, not the kernel driver,
>      is primarily responsible for pinging under normal operation.
> 
>   Documentation/watchdog/watchdog-api.rst | 65 +++++++++++++++++++++----
>   1 file changed, 55 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/watchdog/watchdog-api.rst b/Documentation/watchdog/watchdog-api.rst
> index 78e228c272cf..736436a68f65 100644
> --- a/Documentation/watchdog/watchdog-api.rst
> +++ b/Documentation/watchdog/watchdog-api.rst
> @@ -2,7 +2,7 @@
>   The Linux Watchdog driver API
>   =============================
>   
> -Last reviewed: 10/05/2007
> +Last reviewed: 04/08/2026
>   
>   
>   
> @@ -42,7 +42,7 @@ 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 source file:  see samples/watchdog/watchdog-simple.c
> +like this source file: see samples/watchdog/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.
> @@ -106,11 +106,10 @@ the requested one due to limitation of the hardware::
>   This example might actually print "The timeout was set to 60 seconds"
>   if the device has a granularity of minutes for its timeout.
>   
> -Starting with the Linux 2.4.18 kernel, it is possible to query the
> -current timeout using the GETTIMEOUT ioctl::
> +It is also possible to get the current timeout with the GETTIMEOUT ioctl::
>   
>       ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
> -    printf("The timeout was is %d seconds\n", timeout);
> +    printf("The timeout is %d seconds\n", timeout);
>   
>   Pretimeouts
>   ===========
> @@ -133,7 +132,7 @@ 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);
> +    printf("The pretimeout is %d seconds\n", timeout);
>   
>   Not all watchdog drivers will support a pretimeout.
>   
> @@ -145,12 +144,12 @@ 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);
> +    printf("The timeleft is %d seconds\n", timeleft);
>   
>   Environmental monitoring
>   ========================
>   
> -All watchdog drivers are required return more information about the system,
> +All watchdog drivers are required to return more information about the system,
>   some do temperature, fan and power level monitoring, some can tell you
>   the reason for the last reboot of the system.  The GETSUPPORT ioctl is
>   available to ask what the device can do::
> @@ -227,12 +226,33 @@ The watchdog saw a keepalive ping since it was last queried.
>   	WDIOF_SETTIMEOUT	Can set/get the timeout
>   	================	=======================
>   
> -The watchdog can do pretimeouts.
> +The watchdog supports timeout set/get via the WDIOC_SETTIMEOUT and
> +WDIOC_GETTIMEOUT ioctls.
>   
>   	================	================================
>   	WDIOF_PRETIMEOUT	Pretimeout (in seconds), get/set
>   	================	================================
>   
> +The watchdog supports a pretimeout, a warning interrupt that fires before
> +the actual reboot timeout. Use WDIOC_SETPRETIMEOUT and WDIOC_GETPRETIMEOUT
> +to set/get the pretimeout.
> +
> +	================	================================
> +	WDIOF_MAGICCLOSE	Supports magic close char
> +	================	================================
> +
> +The driver supports the Magic Close feature. The watchdog is only disabled
> +if the character 'V' is written to /dev/watchdog before the file descriptor
> +is closed. Without writing 'V' before closing, the watchdog remains active
> +and will trigger a reboot after the timeout expires.
> +
> +	================	================================
> +	WDIOF_ALARMONLY		Not a reboot watchdog
> +	================	================================
> +
> +The watchdog will not reboot the system when it expires. Instead it
> +triggers a management or other external alarm. Userspace should not
> +rely on a system reboot occurring.
>   
>   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
> @@ -254,6 +274,11 @@ returned value is the temperature in degrees Fahrenheit::
>       int temperature;
>       ioctl(fd, WDIOC_GETTEMP, &temperature);
>   
> +.. note::
> +	``WDIOC_GETTEMP`` is not implemented by the watchdog core and is
> +	considered deprecated. It is only supported by a small number of
> +	legacy drivers. New drivers should not implement it.
> +
>   Finally the SETOPTIONS ioctl can be used to control some aspects of
>   the cards operation::
>   
> @@ -268,4 +293,24 @@ The following options are available:
>   	WDIOS_TEMPPANIC		Kernel panic on temperature trip
>   	=================	================================
>   
> -[FIXME -- better explanations]
> +``WDIOS_DISABLECARD`` disables the hardware watchdog timer entirely,
> +allowing a controlled system shutdown without triggering a reboot.
> +Userspace is responsible for pinging the watchdog under normal
> +operation; this ioctl stops the underlying hardware timer so that
> +the absence of pings no longer causes a system reset.
> +
> +``WDIOS_ENABLECARD`` starts the watchdog timer. If the watchdog was
> +previously stopped via ``WDIOS_DISABLECARD``, this will re-enable it. The
> +hardware watchdog will begin counting down from the configured timeout.
> +
> +``WDIOS_TEMPPANIC`` enables temperature-based kernel panic. When set,
> +the driver will call ``panic()`` (or ``kernel_power_off()`` on some
> +drivers) if the hardware temperature sensor exceeds its threshold,
> +rather than only setting the ``WDIOF_OVERHEAT`` status bit. Support
> +for this option is driver-specific; not all watchdog drivers implement
> +temperature monitoring.
> +
> +.. note::
> +	``WDIOS_TEMPPANIC`` is not implemented by the watchdog core and is
> +	considered deprecated. It is only present in a small number of
> +	legacy drivers. New drivers should not implement it.