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@xxxxxxxxxx> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx> Signed-off-by: Matthew Wood <thepacketgeek@xxxxxxxxx> --- Documentation/networking/netconsole.rst | 66 +++++++++++++++++++++++++ 1 file changed, 66 insertions(+) diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst index 390730a74332..b28c525e5d1e 100644 --- a/Documentation/networking/netconsole.rst +++ b/Documentation/networking/netconsole.rst @@ -15,6 +15,8 @@ Extended console support by Tejun Heo <tj@xxxxxxxxxx>, May 1 2015 Release prepend support by Breno Leitao <leitao@xxxxxxxxxx>, Jul 7 2023 +Userdata append support by Matthew Wood <thepacketgeek@xxxxxxxxx>, Jan 22 2024 + Please send bug reports to Matt Mackall <mpm@xxxxxxxxxxx> Satyam Sharma <satyam.sharma@xxxxxxxxx>, and Cong Wang <xiyou.wangcong@xxxxxxxxx> @@ -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: ================= -- 2.43.0
