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net: netconsole: add docs for appending netconsole user data

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Add a new User Data section to the netconsole docs to describe the
appending of user data capability (for netconsole dynamic configuration)
with usage and netconsole output examples.

Co-developed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Matthew Wood <thepacketgeek@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Matthew Wood 2024-02-04 15:27:35 -08:00 committed by David S. Miller
parent ae001dc679
commit aa7b608d69
1 changed files with 66 additions and 0 deletions
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66
Documentation/networking/netconsole.rst
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@ -15,6 +15,8 @@ Extended console support by Tejun Heo <tj@kernel.org>, May 1 2015
Release prepend support by Breno Leitao <leitao@debian.org>, Jul 7 2023
Userdata append support by Matthew Wood <thepacketgeek@gmail.com>, Jan 22 2024
Please send bug reports to Matt Mackall <mpm@selenic.com>
Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
@ -171,6 +173,70 @@ You can modify these targets in runtime by creating the following targets::
cat cmdline1/remote_ip
10.0.0.3
Append User Data
----------------
Custom user data can be appended to the end of messages with netconsole
dynamic configuration enabled. User data entries can be modified without
changing the "enabled" attribute of a target.
Directories (keys) under `userdata` are limited to 54 character length, and
data in `userdata/<key>/value` are limited to 200 bytes::
cd /sys/kernel/config/netconsole && mkdir cmdline0
cd cmdline0
mkdir userdata/foo
echo bar > userdata/foo/value
mkdir userdata/qux
echo baz > userdata/qux/value
Messages will now include this additional user data::
echo "This is a message" > /dev/kmsg
Sends::
12,607,22085407756,-;This is a message
foo=bar
qux=baz
Preview the userdata that will be appended with::
cd /sys/kernel/config/netconsole/cmdline0/userdata
for f in `ls userdata`; do echo $f=$(cat userdata/$f/value); done
If a `userdata` entry is created but no data is written to the `value` file,
the entry will be omitted from netconsole messages::
cd /sys/kernel/config/netconsole && mkdir cmdline0
cd cmdline0
mkdir userdata/foo
echo bar > userdata/foo/value
mkdir userdata/qux
The `qux` key is omitted since it has no value::
echo "This is a message" > /dev/kmsg
12,607,22085407756,-;This is a message
foo=bar
Delete `userdata` entries with `rmdir`::
rmdir /sys/kernel/config/netconsole/cmdline0/userdata/qux
.. warning::
When writing strings to user data values, input is broken up per line in
configfs store calls and this can cause confusing behavior::
mkdir userdata/testing
printf "val1\nval2" > userdata/testing/value
# userdata store value is called twice, first with "val1\n" then "val2"
# so "val2" is stored, being the last value stored
cat userdata/testing/value
val2
It is recommended to not write user data values with newlines.
Extended console:
=================