Merge branch 'netconsole-userdata-append'

Matthew Wood says:

====================
netconsole: Add userdata append support

Add the ability to add custom userdata to every outbound netconsole message
as a collection of key/value pairs, allowing users to add metadata to every
netconsole message which can be used for  for tagging, filtering, and
aggregating log messages.

In a previous patch series the ability to prepend the uname release was
added towards the goals above. This patch series builds on that
idea to allow any userdata, keyed by a user provided name, to be
included in netconsole messages.

If CONFIG_NETCONSOLE_DYNAMIC is enabled an additional userdata
directory will be presented in the netconsole configfs tree, allowing
the addition of userdata entries.

    /sys/kernel/config/netconsole/
			<target>/
				enabled
				release
				dev_name
				local_port
				remote_port
				local_ip
				remote_ip
				local_mac
				remote_mac
				userdata/
					<key>/
						value
					<key>/
						value
          ...

v1->v2:
 * Updated netconsole_target docs, kdoc is now clean
v2->v3:
 * Remove inline keyword from to_userdat* functions
 * Break up some lines that exceeded 80 chars
 * Replace typos and remove {} from single line if statement
 * Remove unused variable

Testing for this series is as follows:

Build every patch without CONFIG_NETCONSOLE_DYNAMIC, and also built
with CONFIG_NETCONSOLE_DYNAMIC enabled for every patch after the config
option was added

Test Userdata configfs

    # Adding userdata
    cd /sys/kernel/config/netconsole/ && mkdir cmdline0 && cd cmdline0
    mkdir userdata/release && echo hotfix1 > userdata/release/value
    preview=$(for f in `ls userdata`; do echo $f=$(cat userdata/$f/value); done)
    [[ "$preview" == $'release=hotfix1' ]] && echo pass || echo fail
    mkdir userdata/testing && echo something > userdata/testing/value
    preview=$(for f in `ls userdata`; do echo $f=$(cat userdata/$f/value); done)
    [[ "$preview" == $'release=hotfix1\ntesting=something' ]] && echo pass || echo fail
    #
    # Removing Userdata
    rmdir userdata/testing
    preview=$(for f in `ls userdata`; do echo $f=$(cat userdata/$f/value); done)
    [[ "$preview" == $'release=hotfix1' ]] && echo pass || echo fail
    rmdir userdata/release
    preview=$(for f in `ls userdata`; do echo $f=$(cat userdata/$f/value); done)
    [[ "$preview" == $'' ]] && echo pass || echo fail
    #
    # Adding userdata key with too large of 6.7.0-rc8-virtme,12,481,17954104,-directory name [<54 chars]
    mkdir userdata/testing12345678901234567890123456789012345678901234567890
    [[ $? == 1 ]] && echo pass || echo fail
    #
    # Adding userdata value with too large of value [<200 chars]
    mkdir userdata/testing
    echo `for i in {1..201};do printf "%s" "v";done` > userdata/testing/value
    [[ $? == 1 ]] && echo pass || echo fail
    rmdir userdata/testing

- Output:

    pass
    pass
    pass
    pass
    pass
    mkdir: cannot create directory ‘cmdline0/userdata/testing12345678901234567890123456789012345678901234567890’: File name too long
    pass
    bash: echo: write error: Message too long
    pass

Test netconsole messages (w/ msg fragmentation)

    echo `for i in {1..996};do printf "%s" "v";done` > /dev/kmsg

- Output:

    6.7.0-rc8-virtme,12,484,84321212,-,ncfrag=0/997;vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv6.7.0-rc8-virtme,12,484,84321212,-,ncfrag=952/997;vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

Test empty userdatum

    cd /sys/kernel/config/netconsole/ && mkdir cmdline0
    mkdir cmdline0/userdata/empty
    echo test > /dev/kmsg
    rmdir cmdline0/userdata/empty

- Output:

Test netconsole messages (w/o userdata fragmentation)

    cd /sys/kernel/config/netconsole/ && mkdir cmdline0
    mkdir cmdline0/userdata/release && echo hotfix1 > cmdline0/userdata/release/value
    mkdir cmdline0/userdata/testing && echo something > cmdline0/userdata/testing/value
    echo test > /dev/kmsg
    rmdir cmdline0/userdata/release
    rmdir cmdline0/userdata/testing
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/netconsole.rst

@@ -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:
 =================