Update the netconsole documentation to explain the new feature that allows automatic population of the CPU number.
The key changes include introducing a new section titled "CPU number auto population in userdata", explaining how to enable the CPU number auto-population feature by writing to the "populate_cpu_nr" file in the netconsole configfs hierarchy.
This documentation update ensures users are aware of the new CPU number auto-population functionality and how to leverage it for better demultiplexing and visibility of parallel netconsole output.
Signed-off-by: Breno Leitao leitao@debian.org --- Documentation/networking/netconsole.rst | 45 +++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+)
diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst index 94c4680fdf3e7e1a0020d11b44547acfd68072a5..84803c59968a3237012fab821f432eb531aba45c 100644 --- a/Documentation/networking/netconsole.rst +++ b/Documentation/networking/netconsole.rst @@ -17,6 +17,8 @@ Release prepend support by Breno Leitao leitao@debian.org, Jul 7 2023
Userdata append support by Matthew Wood thepacketgeek@gmail.com, Jan 22 2024
+Sysdata append support by Breno Leitao leitao@debian.org, Jan 15 2025 + Please send bug reports to Matt Mackall mpm@selenic.com Satyam Sharma satyam.sharma@gmail.com, and Cong Wang xiyou.wangcong@gmail.com
@@ -238,6 +240,49 @@ Delete `userdata` entries with `rmdir`::
It is recommended to not write user data values with newlines.
+CPU number auto population in userdata +-------------------------------------- + +Inside the netconsole configfs hierarchy, there is a file called +`cpu_nr` under the `userdata` directory. This file is used to enable or disable +the automatic CPU number population feature. This feature automatically +populates the CPU number that is sending the message. + +To enable the CPU number auto-population:: + + echo 1 > /sys/kernel/config/netconsole/target1/userdata/cpu_nr + +When this option is enabled, the netconsole messages will include an additional +line in the userdata field with the format `cpu=<cpu_number>`. This allows the +receiver of the netconsole messages to easily differentiate and demultiplex +messages originating from different CPUs, which is particularly useful when +dealing with parallel log output. + +Example:: + + echo "This is a message" > /dev/kmsg + 12,607,22085407756,-;This is a message + cpu=42 + +In this example, the message was sent by CPU 42. + +.. note:: + + If the user has set a conflicting `cpu` key in the userdata dictionary, + both keys will be reported, with the kernel-populated entry appearing after + the user one. For example:: + + # User-defined CPU entry + mkdir -p /sys/kernel/config/netconsole/target1/userdata/cpu + echo "1" > /sys/kernel/config/netconsole/target1/userdata/cpu/value + + Output might look like:: + + 12,607,22085407756,-;This is a message + cpu=1 + cpu=42 # kernel-populated value + + Extended console: =================