linux-kernel - [PATCH net-next 5/5] docs: netconsole: document msgid feature

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Message-Id: <20250611-netconsole-msgid-v1-5-1784a51feb1e@gmail.com>
Date: Wed, 11 Jun 2025 07:36:07 -0700
From: Gustavo Luiz Duarte <gustavold@...il.com>
To: Breno Leitao <leitao@...ian.org>, Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Shuah Khan <shuah@...nel.org>, Simon Horman <horms@...nel.org>, 
 Jonathan Corbet <corbet@....net>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org, 
 Gustavo Luiz Duarte <gustavold@...il.com>
Subject: [PATCH net-next 5/5] docs: netconsole: document msgid feature

Add documentation explaining the msgid feature in netconsole.

This feature appends unique id to the userdata dictionary. The message
ID is populated from a per-target 32 bit counter which is incremented
for each message sent to the target. This allows a target to detect if
messages are dropped before reaching the target.

Signed-off-by: Gustavo Luiz Duarte <gustavold@...il.com>
---
 Documentation/networking/netconsole.rst | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index a0076b542e9c..42a0acf2eb5e 100644
--- a/Documentation/networking/netconsole.rst
+++ b/Documentation/networking/netconsole.rst
@@ -340,6 +340,28 @@ In this example, the message was sent by CPU 42.
       cpu=42    # kernel-populated value

+Message ID auto population in userdata
+--------------------------------------
+
+Within the netconsole configfs hierarchy, there is a file named `msgid_enabled`
+located in the `userdata` directory. This file controls the message ID
+auto-population feature, which assigns a unique id to each message sent to a
+given target and appends the ID to userdata dictionary in every message sent.
+
+The message ID is built from a per-target 32 bit counter that is incremented
+for every message sent to the target. This ID can be used by the target to
+detect if messages were dropped before reaching the target.
+
+Example::
+
+  echo "This is message #1" > /dev/kmsg
+  echo "This is message #2" > /dev/kmsg
+  13,434,54928466,-;This is message #1
+   msgid=1
+  13,435,54934019,-;This is message #2
+   msgid=2
+
+
 Extended console:
 =================

-- 
2.47.1