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

From:  Andrew Morton <akpm-AT-linux-foundation.org>
To:  Steven Rostedt <rostedt-AT-goodmis.org>
Subject:  Re: [PATCH] printk: Add printk_flush() to force buffered text to console
Date:  Fri, 22 Jun 2012 16:49:17 -0700
Message-ID:  <20120622164917.3121168a.akpm@linux-foundation.org>
Cc:  LKML <linux-kernel-AT-vger.kernel.org>, Linus Torvalds <torvalds-AT-linux-foundation.org>, Greg Kroah-Hartman <gregkh-AT-linuxfoundation.org>, "kay.sievers" <kay.sievers-AT-vrfy.org>, Fengguang Wu <fengguang.wu-AT-intel.com>, Ingo Molnar <mingo-AT-elte.hu>
Archive-link:  Article

On Fri, 22 Jun 2012 19:41:04 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 2012-06-22 at 14:54 -0700, Andrew Morton wrote:
> > On Thu, 21 Jun 2012 19:52:03 -0400
> > Steven Rostedt <rostedt@goodmis.org> wrote:
> > 
> > > But with the new printk() changes, text without a newline gets buffered
> > > and does not print out to the console at the location of the printk.
> > 
> > uh, how about we fix that?  The old behaviour was good, the new
> > behaviour is noxious.
> > 
> > Please idenfity these "new printk() changes".  Was the new noxiousness
> > an unavoidable effect of them?
> 
> See commit 7ff9554bb578 ("printk: convert byte-buffer to variable-length
> record buffer") and related commits.
> 
> But that said, there may be a way that I can make it still always flush
> and not add a new API. We can flush on partial writes, and keep track of
> the current task (as it already does). If a new task comes in, we can
> then force a newline before printing the content of the old task (if
> there wasn't a newline printed before).
> 
> This is basically what it does now, except that it buffers the data. If
> a new task were to do a print in between the two partial writes, it
> flushes what was buffered and adds a newline before printing the new
> text.

If a driver does

	printk("testing the frobnozzle ...");
	do_test();
	printk(" OK\n");

and do_test() hangs up, we really really want the user to know that
there was a frobnozzle testing problem.  Please tell me this isn't
broken.


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