Re: [PATCH net-next v2 5/5] netconsole: docs: Add documentation for CPU number auto-population
From: Randy Dunlap <rdunlap@infradead.org>
Date: 2025-01-15 22:56:55
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linux-doc, linux-kselftest, lkml
On 1/15/25 5:35 AM, Breno Leitao wrote:
quoted hunk ↗ jump to hunk
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: =================
-- ~Randy