linux-kernel - [PATCH net-next] net: netconsole: Add continuation line prefix to userdata messages

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Date: Wed, 28 Feb 2024 09:29:46 -0800
From: Matthew Wood <thepacketgeek@...il.com>
To: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Breno Leitao <leitao@...ian.org>
Cc: netdev@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net-next] net: netconsole: Add continuation line prefix to userdata messages

Add a space (' ') prefix to every userdata line to match docs for
dev-kmsg. To account for this extra character in each userdata entry,
reduce userdata entry names (directory name) from 54 characters to 53.

According to the dev-kmsg docs, a space is used for subsequent lines to
mark them as continuation lines.

> A line starting with ' ', is a continuation line, adding
> key/value pairs to the log message, which provide the machine
> readable context of the message, for reliable processing in
> userspace.

Testing for this patch::

 cd /sys/kernel/config/netconsole && mkdir cmdline0
 cd cmdline0
 mkdir userdata/test && echo "hello" > userdata/test/value
 mkdir userdata/test2 && echo "hello2" > userdata/test2/value
 echo "message" > /dev/kmsg

Outputs::

 6.8.0-rc5-virtme,12,493,231373579,-;message
  test=hello
  test2=hello2

And I confirmed all testing works as expected from the original patchset

Fixes: df03f830d099 ("net: netconsole: cache userdata formatted string in netconsole_target")
Signed-off-by: Matthew Wood <thepacketgeek@...il.com>
---
 Documentation/networking/netconsole.rst | 6 +++---
 drivers/net/netconsole.c                | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index b28c525e5d1e..c2dec12f6060 100644
--- a/Documentation/networking/netconsole.rst
+++ b/Documentation/networking/netconsole.rst
@@ -197,8 +197,8 @@ Messages will now include this additional user data::
 Sends::
 
  12,607,22085407756,-;This is a message
- foo=bar
- qux=baz
+  foo=bar
+  qux=baz
 
 Preview the userdata that will be appended with::
 
@@ -218,7 +218,7 @@ 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
+  foo=bar
 
 Delete `userdata` entries with `rmdir`::
 
diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 0de108a1c0c8..ffd3e19406b5 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -43,7 +43,7 @@ MODULE_DESCRIPTION("Console driver for network interfaces");
 MODULE_LICENSE("GPL");
 
 #define MAX_PARAM_LENGTH	256
-#define MAX_USERDATA_NAME_LENGTH	54
+#define MAX_USERDATA_NAME_LENGTH	53 /* 256 - 200 - 3 (for ' =\n' chars)*/
 #define MAX_USERDATA_VALUE_LENGTH	200
 #define MAX_USERDATA_ENTRY_LENGTH	256
 #define MAX_USERDATA_ITEMS		16
@@ -671,7 +671,7 @@ static void update_userdata(struct netconsole_target *nt)
 		 * checked to not exceed MAX items with child_count above
 		 */
 		complete_idx += scnprintf(&nt->userdata_complete[complete_idx],
-					  MAX_USERDATA_ENTRY_LENGTH, "%s=%s\n",
+					  MAX_USERDATA_ENTRY_LENGTH, " %s=%s\n",
 					  item->ci_name, udm_item->value);
 	}
 	nt->userdata_length = strnlen(nt->userdata_complete,
-- 
2.43.2