linux-kernel - Re: [RFC PATCH v5 1/3] printk-rb: new printk ringbuffer implementation (writer)

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Date:   Mon, 9 Dec 2019 18:27:56 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        kexec@...ts.infradead.org
Subject: Re: [RFC PATCH v5 1/3] printk-rb: new printk ringbuffer
 implementation (writer)

On (19/11/28 02:58), John Ogness wrote:
> + * Sample reader code::
> + *
> + *	struct printk_info info;
> + *	char text_buf[32];
> + *	char dict_buf[32];
> + *	u64 next_seq = 0;
> + *	struct printk_record r = {
> + *		.info		= &info,
> + *		.text_buf	= &text_buf[0],
> + *		.dict_buf	= &dict_buf[0],
> + *		.text_buf_size	= sizeof(text_buf),
> + *		.dict_buf_size	= sizeof(dict_buf),
> + *	};
> + *
> + *	while (prb_read_valid(&rb, next_seq, &r)) {
> + *		if (info.seq != next_seq)
> + *			pr_warn("lost %llu records\n", info.seq - next_seq);
> + *
> + *		if (info.text_len > r.text_buf_size) {
> + *			pr_warn("record %llu text truncated\n", info.seq);
> + *			text_buf[sizeof(text_buf) - 1] = 0;
> + *		}
> + *
> + *		if (info.dict_len > r.dict_buf_size) {
> + *			pr_warn("record %llu dict truncated\n", info.seq);
> + *			dict_buf[sizeof(dict_buf) - 1] = 0;
> + *		}
> + *
> + *		pr_info("%llu: %llu: %s;%s\n", info.seq, info.ts_nsec,
> + *			&text_buf[0], info.dict_len ? &dict_buf[0] : "");
> + *
> + *		next_seq = info.seq + 1;
> + *	}
> + */

Will this loop ever end? :)

pr_info() adds data to ringbuffer, which prb_read_valid() reads, so pr_info()
can add more data, which prb_read_valid() will read, so pr_info()...

	-ss