Update the netconsole documentation to explain the new feature that
allows automatic population of the CPU number in the userdata field.
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@xxxxxxxxxx>
---
Documentation/networking/netconsole.rst | 44 +++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)
diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index d55c2a22ec7af0e687b76176c9171eb1b19013bd..a1b269196be390b5f88a6eca77f6676c67c05720 100644
--- a/Documentation/networking/netconsole.rst
+++ b/Documentation/networking/netconsole.rst
@@ -237,6 +237,50 @@ 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
+`populate_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 in the
+userdata field.
+
+To enable the CPU number auto-population::
+
+ echo 1 > /sys/kernel/config/netconsole/target1/userdata/populate_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:
=================
--
2.43.5
