linux-kernel - Re: [PATCH] printk: Increase PRINTK_PREFIX_MAX and the buf size in print

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Date: Mon, 27 May 2024 16:54:56 +0200
From: Petr Mladek <pmladek@...e.com>
To: Xiang Gao <gxxa03070307@...il.com>
Cc: rostedt@...dmis.org, john.ogness@...utronix.de,
	senozhatsky@...omium.org, linux-kernel@...r.kernel.org,
	fengqi@...omi.com, xiaoa <gaoxiang19870307@....com>
Subject: Re: [PATCH] printk: Increase PRINTK_PREFIX_MAX and the buf size in
 print_caller.

On Mon 2024-05-27 17:19:29, Xiang Gao wrote:
> Sometimes we need to add our own hooks to carry more caller information
> to improve debug efficiency, but currently the buf in print caller is
> too small.

> --- a/kernel/printk/internal.h
> +++ b/kernel/printk/internal.h
> @@ -23,7 +23,7 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
>  #ifdef CONFIG_PRINTK
>  
>  #ifdef CONFIG_PRINTK_CALLER
> -#define PRINTK_PREFIX_MAX	48
> +#define PRINTK_PREFIX_MAX	64
>  #else
>  #define PRINTK_PREFIX_MAX	32
>  #endif
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 420fd310129d..2d7f003113f7 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1331,7 +1331,7 @@ static size_t print_time(u64 ts, char *buf)
>  #ifdef CONFIG_PRINTK_CALLER
>  static size_t print_caller(u32 id, char *buf)
>  {
> -	char caller[12];
> +	char caller[32];

Could you provide more details, please?
How exactly do you add your own hooks?

If you need to modify the code to add the extra info, you could also
modify the buffer size.

The buffer is big enough for the info printed by the upstream code.
I do understand why we should do this change upstream.

>  	snprintf(caller, sizeof(caller), "%c%u",
>  		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);


Best Regards,
Petr