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Date:   Thu, 23 Nov 2017 11:59:57 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Kevin Hilman <khilman@...libre.com>,
        Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: kernel CI: printk loglevels in kernel boot logs?

On (11/22/17 20:52), Fengguang Wu wrote:
[..]
> > well, I think that that "consoles_format=syslog" command line parameter
> > will be enabled only by those who actually want to have it - Fengguang's
> > build robot and kernelCI (+ may be more setups).  so I'd probably assume
> > there are low risks here. may be I'm wrong.
> 
> Yes, since it needs explicit enabling, local parsers should stay
> working. Unless we send dmesg to other developers, but then they
> might also receive $(dmesg --raw) outputs and need to handle <%u>
> prefixes, too.
> 
> > I think it makes sense to have syslog's format "<%u>[timestamp] text\n"
> > on serial consoles (time stamp when PRINTK_TIME set; <%u> when
> > consoles_format=syslog set).
> 
> Thanks. Since the 0day scripts can already parse that format (code
> is listed below), we should quickly benefit from that feature when
> it's mainlined.

okay... who's going to send the patch? kernelCI folks?

I have some sort of a patch. added console_msg_format= with the only
available option so far - "syslog". may be people would want to have
boot time, etc. on their consoles. who knows. may be msg_format will
be extended someday in the future or may be not, and we can do
something like "console_format_syslog" (or any better name).

Not-yet-signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++++
 kernel/printk/printk.c                          | 21 ++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 62436bd5f34a..42113e5181b2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -640,6 +640,17 @@
 			console=brl,ttyS0
 		For now, only VisioBraille is supported.
 
+	console_msg_format=
+			[KNL] Control message format
+			By default we print messages 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 (similar to "dmesg --raw" or
+			reading from /proc/kmsg): "<%u>[time stamp] text\n"
+			IOW, each message is getting prepended with the
+			facility and loglevel prefix.
+
 	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 5d81206a572d..034f3ad85f5b 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 = 1,
+	MSG_FORMAT_SYSLOG = 2,
+};
+
+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 +1920,15 @@ 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;
+	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 +2231,10 @@ 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),
-- 
2.15.0

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