Re: [PATCH net-next v2] net: netconsole: Add continuation line prefix to userdata messages

Breno Leitao
2024-03-01T09:35:49Z

On Thu, Feb 29, 2024 at 10:36:01AM -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
>
> 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)

I think the changelog needs to come after the --- below, but I will
defer that to the maintainers.

> Fixes: df03f830d099 ("net: netconsole: cache userdata formatted string in netconsole_target")
> Signed-off-by: Matthew Wood <thepacketgeek@gmail.com>
> ---
> Documentation/networking/netconsole.rst | 8 ++++----
> drivers/net/netconsole.c | 8 +++++---
> 2 files changed, 9 insertions(+), 7 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..46e447ea41b8 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -43,9 +43,11 @@ 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_USERDATA_ENTRY_LENGTH 256
> +#define MAX_USERDATA_VALUE_LENGTH 200
> +#define MAX_USERDATA_NAME_LENGTH MAX_USERDATA_ENTRY_LENGTH - \
> + MAX_USERDATA_VALUE_LENGTH - \
> + 3 /* ' ' '=' '\n' characters */

This is not beautiful even for my standards. I think something like the
code below makes more sense, even if checkpatch is not happy.

/* The number three below comes from ' ' + '=' + '\n' characters */
#define MAX_USERDATA_NAME_LENGTH MAX_USERDATA_ENTRY_LENGTH - MAX_USERDATA_VALUE_LENGTH - 3