linux-kernel - Re: [PATCH net-next v3] net: netconsole: Add continuation line prefix to userdata messages

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Message-ID: <8a3ccdc5445d0cfda36418dd50746f13f447bdaa.camel@redhat.com>
Date: Tue, 05 Mar 2024 13:14:13 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Matthew Wood <thepacketgeek@...il.com>, "David S. Miller"
	 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	 <kuba@...nel.org>, 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: Re: [PATCH net-next v3] net: netconsole: Add continuation line
 prefix to userdata messages

On Fri, 2024-03-01 at 10:58 -0800, Matthew Wood wrote:
> 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")
> Reviewed-by: Breno Leitao <leitao@...ian.org>

I guess the tag arrived off-list, because I can't see any sign of it on
the ML?!?

> Signed-off-by: Matthew Wood <thepacketgeek@...il.com>
> ---
> 
> v1 -> v2:
> - Calculate 53 byte user data name from: entry length - formatting chars - value length
> - Update docs to reflect 53 byte limit for user data name (director)
> v2 -> v3:
> - Added #define for userdata formatting character length (3)
> - Matched all #defines indent level
> 
>  Documentation/networking/netconsole.rst |  8 ++++----
>  drivers/net/netconsole.c                | 14 +++++++++-----
>  2 files changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
> index b28c525e5d1e..d55c2a22ec7a 100644
> --- a/Documentation/networking/netconsole.rst
> +++ b/Documentation/networking/netconsole.rst
> @@ -180,7 +180,7 @@ 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
> +Directories (keys) under `userdata` are limited to 53 character length, and
>  data in `userdata/<key>/value` are limited to 200 bytes::
>  
>   cd /sys/kernel/config/netconsole && mkdir cmdline0
> @@ -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..8cc28aec59c8 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -42,12 +42,16 @@ MODULE_AUTHOR("Maintainer: Matt Mackall <mpm@...enic.com>");
>  MODULE_DESCRIPTION("Console driver for network interfaces");
>  MODULE_LICENSE("GPL");
>  
> -#define MAX_PARAM_LENGTH	256
> -#define MAX_USERDATA_NAME_LENGTH	54
> -#define MAX_USERDATA_VALUE_LENGTH	200
> +#define MAX_PARAM_LENGTH		256
> +/* characters used for formatting each userdata entry line (' ', '=', '\n') */
> +#define USERDATA_FORMAT_CHARS		3
>  #define MAX_USERDATA_ENTRY_LENGTH	256
> +#define MAX_USERDATA_VALUE_LENGTH	200
> +#define MAX_USERDATA_NAME_LENGTH	MAX_USERDATA_ENTRY_LENGTH - \
> +					MAX_USERDATA_VALUE_LENGTH - \
> +					USERDATA_FORMAT_CHARS

AFAICS this is not what Breno asked, and checkpatch complains
rightfully. More importantly it's fragile: what will be the result of

	MAX_USERDATA_NAME_LENGTH * 2

?

At least some brackets are required:

#define MAX_USERDATA_NAME_LENGTH	(MAX_USERDATA_ENTRY_LENGTH -
					 MAX_USERDATA_VALUE_LENGTH - \
					 USERDATA_FORMAT_CHARS)

Thanks,

Paolo