linux-kernel - Re: [PATCH] printk: Add printk_flush() to force buffered text to console

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Date:	Thu, 21 Jun 2012 11:17:03 -0700
From:	Joe Perches <joe@...ches.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"kay.sievers" <kay.sievers@...y.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] printk: Add printk_flush() to force buffered text to
 console

On Thu, 2012-06-21 at 13:41 -0400, Steven Rostedt wrote:
> On Thu, 2012-06-21 at 10:13 -0700, Greg Kroah-Hartman wrote:
> 
> > > So mind re-sending the latest version of your printk flushing 
> > > fix? I'll apply it for v3.5-rc if other trees won't pick it up.
> > 
> > I'll be glad to pick it up, just make it work properly :)
> 
> I'm playing around with making a KERN_FLUSH "<f>". Think that's a better
> approach?

I don't think that's better.  I think it's worse
because it intermixes the idea of a kernel message
logging level with a specific functionality to
emit any fragmentary message immediately.

I think a global setting via a some functions like:

(printk private variable)
bool printk_buffered = true;

bool printk_set_buffering(bool enable)
{
	bool old_state = printk_buffered;
	printk_buffered = enable;

	return old_state;
}

and maybe:

bool printk_get_buffering(void)
{
	return printk_buffered;
}

would be better because the non-buffered use should
really be pretty isolated to last_breath type output
and to pretty isolated cases like your long running
tests.

A separate printk_flush() function if really necessary
but sprinking a bunch of printk_flush() calls seems
wasteful.


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