On 1/15/25 5:35 AM, Breno Leitao wrote:

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..bc9ccebdae7adadd7c57aef20a726536d7ab3173 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 +populate the CPU number that is sending the message.

populates

+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: