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

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Message-ID: <1340408464.27036.282.camel@gandalf.stny.rr.com>
Date:	Fri, 22 Jun 2012 19:41:04 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"kay.sievers" <kay.sievers@...y.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] printk: Add printk_flush() to force buffered text to
 console

On Fri, 2012-06-22 at 14:54 -0700, Andrew Morton wrote:
> On Thu, 21 Jun 2012 19:52:03 -0400
> Steven Rostedt <rostedt@...dmis.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.

I think I may be able to implement the same behavior, except that it
wont buffer. It would just keep track of the state of the last write.

-- Steve

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