linux-kernel - Re: [PATCH printk v2 1/7] printk: Move buffer size defines

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Date:   Thu, 24 Nov 2022 12:09:25 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH printk v2 1/7] printk: Move buffer size defines

On Thu 2022-11-24 00:19:54, John Ogness wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Move the buffer size defines to console.h in preparation of adding a
> buffer structure. The new buffer structure will be embedded within
> struct console. Therefore console.h was chosen as the new home for
> these defines.

The buffers are not embedded into struct console in this patchset.
Are they going to be added directly or via pointer, please?

IMHO, it is always better to hide these implementation details
in an internal header or source file. It will be possible
if struct console contained on a pointer to the buffers.

> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
>  include/linux/console.h | 14 ++++++++++++++
>  include/linux/printk.h  |  2 --
>  kernel/printk/printk.c  |  4 ----
>  3 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/console.h b/include/linux/console.h
> index 9cea254b34b8..799fc3216aad 100644
> --- a/include/linux/console.h
> +++ b/include/linux/console.h
> @@ -122,6 +122,20 @@ static inline int con_debug_leave(void)
>  #define CM_ERASE    (2)
>  #define CM_MOVE     (3)
>  
> +#ifdef CONFIG_PRINTK
> +
> +/* The maximum size of a formatted record (i.e. with prefix added per line) */
> +#define CONSOLE_LOG_MAX		1024
> +
> +#else
> +
> +#define CONSOLE_LOG_MAX		0
> +
> +#endif
> +
> +/* The maximum size of a formatted extended record */
> +#define CONSOLE_EXT_LOG_MAX	8192

It looks strange that we need the buffer for extended messages
and not the normal one when !CONFIG_PRINTK. I can't find any reason
for this. It looks like a historic inconsistency.

CONSOLE_EXT_LOG_MAX was added into printk.h in the commit
d43ff430f434d862db59 ("printk: guard the amount written per line
by devkmsg_read()"). It didn't have to be in include/linux/printk.h
at that time. But nobody cared, including me, I was a greenhorn ;-)

Well, it would be nice to fix it when we are moving the definition
next to each other.

Best Regards,
Petr