linux-kernel - Re: [PATCH printk v2 2/8] printk: Provide debug

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Date:   Fri, 28 Jul 2023 11:58:44 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v2 2/8] printk: Provide debug_store() for nbcon
 debugging

On 2023-07-28, John Ogness <john.ogness@...utronix.de> wrote:
> +/*
> + * Define DEBUG_NBCON to allow for nbcon ownership transitions to be logged
> + * to the ringbuffer. The debug_store() macro only logs to the lockless
> + * ringbuffer and does not trigger any printing.
> + */
> +#undef DEBUG_NBCON
> +
> +#ifdef DEBUG_NBCON
> +/* Only write to ringbuffer. */
> +int __debug_store(const char *fmt, ...)
> +{
> +	va_list args;
> +	int r;
> +
> +	va_start(args, fmt);
> +	r = vprintk_store(2, 7, NULL, fmt, args);
> +	va_end(args);
> +
> +	return r;
> +}
> +#define debug_store(cond, fmt, ...)						\
> +	do {									\
> +		if (cond)							\
> +			__debug_store(pr_fmt("DEBUG: " fmt), ##__VA_ARGS__)	\

Missing a semi-colon here. Wrapping this with a do-while was a
last-minute change requested by checkpatch.pl. Probably nobody would
notice because you must manually define DEBUG_NBCON by changing the
source code. Fixed for v3 (assuming Petr allows me to keep this
debugging code in place).

> +	} while (0)
> +#else
> +#define debug_store(cond, fmt, ...)
> +#endif

John