linux-kernel - Re: [PATCHv2] printk: add console_msg

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Date:   Tue, 19 Dec 2017 10:17:27 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Kevin Hilman <khilman@...libre.com>,
        Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCHv2] printk: add console_msg_format command line option

On Tue, 19 Dec 2017 17:42:43 +0900
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:

> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 8a61d1eda677..543de386e01e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -642,6 +642,20 @@
>  			console=brl,ttyS0
>  		For now, only VisioBraille is supported.
>  
> +	console_msg_format=
> +			[KNL] Change console messages format
> +		default
> +			By default we print messages on consoles in
> +			"[time stamp] text\n" format (time stamp may not be
> +			printed, depending on CONFIG_PRINTK_TIME or
> +			`printk_time' param).
> +		syslog
> +			Switch to syslog format: "<%u>[time stamp] text\n"
> +			IOW, each message will have a facility and loglevel
> +			prefix. The format is similar to one used by syslog()
> +			syscall, or to executing "dmesg -S --raw" or to reading
> +			from /proc/kmsg.

Just to clarify. This affects all consoles, not just serial?

> +
>  	consoleblank=	[KNL] The console blank (screen saver) timeout in
>  			seconds. A value of 0 disables the blank timer.
>                         Defaults to 0.
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index c2e713f6ae2e..16dd91260273 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -277,6 +277,13 @@ EXPORT_SYMBOL(console_set_on_cmdline);
>  /* Flag: console code may call schedule() */
>  static int console_may_schedule;
>  
> +enum con_msg_format {
> +	MSG_FORMAT_DEFAULT	= 0,
> +	MSG_FORMAT_SYSLOG	= (1 << 0),
> +};

So the con_msg_format will be a flag (as denoted with the (1<<0)).
Should we call it "con_msg_format_flags" to make it more obvious that
these are treated as flags and not a simple number.


> +
> +static int console_msg_format = MSG_FORMAT_DEFAULT;
> +
>  /*
>   * The printk log buffer consists of a chain of concatenated variable
>   * length records. Every record starts with a record header, containing
> @@ -1913,6 +1920,17 @@ static int __add_preferred_console(char *name, int idx, char *options,
>  	c->index = idx;
>  	return 0;
>  }
> +
> +static int __init console_msg_format_setup(char *str)
> +{
> +	if (!strncmp(str, "syslog", 6))
> +		console_msg_format = MSG_FORMAT_SYSLOG;
> +	if (!strncmp(str, "default", 7))

You can use strcmp() instead of strncmp(), the init code will nul
terminate the string for you before calling this function. Otherwise if
we add "syslog_special" or "default_extra" they will be confused with
the above.

-- Steve

> +		console_msg_format = MSG_FORMAT_DEFAULT;
> +	return 1;
> +}
> +__setup("console_msg_format=", console_msg_format_setup);
> +
>  /*
>   * Set up a console.  Called via do_early_param() in init/main.c
>   * for each "console=" parameter in the boot command line.
> @@ -2215,7 +2233,10 @@ void console_unlock(void)
>  			goto skip;
>  		}
>  
> -		len += msg_print_text(msg, false, text + len, sizeof(text) - len);
> +		len += msg_print_text(msg,
> +				console_msg_format & MSG_FORMAT_SYSLOG,
> +				text + len,
> +				sizeof(text) - len);
>  		if (nr_ext_console_drivers) {
>  			ext_len = msg_print_ext_header(ext_text,
>  						sizeof(ext_text),