Commit a7aec70a authored by Breno Leitao's avatar Breno Leitao Committed by David S. Miller
Browse files

netconsole: docs: Add documentation for CPU number auto-population 



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: default avatarBreno Leitao <leitao@debian.org>
Reviewed-by: default avatarSimon Horman <horms@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 12fd83ca

Documentation/networking/netconsole.rst

+45 −0
Original line number Diff line number Diff line
@@ -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:

=================