linux-kernel - Re: [RFC PATCH 2/2] init: Allow multi-line output of kernel command line

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Message-ID: <20200520044127.GB938@jagdpanzerIV.localdomain>
Date:   Wed, 20 May 2020 13:41:27 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Chenggang Wang <wangchenggang@...o.com>,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH 2/2] init: Allow multi-line output of kernel command
 line

On (20/05/19 12:42), Joe Perches wrote:
> +static void __init print_cmdline(char *line)
> +{
> +#ifdef CONFIG_PRINTK
> +	const char *prefix = "Kernel command line";
> +	size_t len = strlen(line);
> +
> +	while (len > PRINTK_LOG_LINE_MAX) {
> +		char *pos = line;
> +		char *last_pos = pos + PRINTK_LOG_LINE_MAX - 1;
> +		char saved_char;
> +		/* Find last space char within the maximum line length */
> +		while ((pos = memchr(pos, ' ', len - (pos - line))) &&
> +		       (pos - line) < PRINTK_LOG_LINE_MAX - 1) {

Don't you need to also count in the 'prefix' length?

> +			last_pos = pos;
> +		}
> +		saved_char = line[last_pos - line];
> +		line[last_pos - line] = 0;
> +		pr_notice("%s: %s\n", prefix, line);
> +		prefix = "Kernel command line (continued)";
> +		line[last_pos - line] = saved_char;
> +		len -= pos - line;
> +		line += pos - line;
> +	}
> +
> +	pr_notice("%s: %s\n", prefix, line);
> +#endif
> +}

I like this in general. And I agree that we better handle this
externally, on the printk() caller side, so that printk() will
still have sane limits and won't print a 1G string for example.

I wonder if we need to export PRINTK_LOG_LINE_MAX. Maybe we can
use here something rather random and much shorter instead. E.g.
256 chars. Hmm. How many crash/monitoring tools can get confused
by multiple "Kernel command line" prefixes?

	-ss