linux-kernel - Re: About multi-line printk and the need (not) to repeat loglevel markers [Was: Re: [PATCH] ARM: mx3/pcm037: properly allocate memory for mx3-camera]

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Date:	Tue, 23 Nov 2010 11:39:40 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: About multi-line printk and the need (not) to repeat loglevel
	markers [Was: Re: [PATCH] ARM: mx3/pcm037: properly allocate memory
	for mx3-camera]

Hello,

[extended the audience to lkml and a few more]

On Tue, Nov 23, 2010 at 10:12:11AM +0000, Russell King - ARM Linux wrote:
> On Tue, Nov 23, 2010 at 10:43:02AM +0100, Uwe Kleine-König wrote:
> > There is no need to memzero the buffer because dma_alloc_coherent zeros
> > the memory for us.
> > 
> > This fixes:
> > 
> > 	BUG: Your driver calls ioremap() on system memory.  This leads
> > 	<4>to architecturally unpredictable behaviour on ARMv6+, and ioremap()
> > 	<4>will fail in the next kernel release.  Please fix your driver.
> > 
> > Tested-by: Michael Grzeschik <mgr@...gutronix.de>
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > ---
> [...]
> > I assume sending a patch to remove the <4> is just a waste of time,
> > isn't it?
(this message is generated by:

	printk(KERN_WARNING "BUG: Your driver calls ioremap() on system memory.  This leads\n"
	       KERN_WARNING "to architecturally unpredictable behaviour on ARMv6+, and ioremap()\n"
	       KERN_WARNING "will fail in the next kernel release.  Please fix your driver.\n");

in arch/arm/mm/ioremap.c.)

> Hmm, someone changed the behaviour of printk - it used to require the
> tag after each newline.  It seems that it only requires it as the first
> few characters now, which is a pain in the backside if you split
> printk's.
> 
> IOW:
> 
> 	printk(KERN_ERR "foo bar baz ");
> 	printk("buz\n" KERN_WARNING "fiz\n");
> 
> used to result in "foo bar baz buz" being printed at error level, and
> "fiz" at warning level.  Today, you'll get "foo bar baz buz" at error
> level, and "<4>fiz" at the default level.
> 
> Note that it's not as simple as deleting the KERN_WARNING, because:
> 	printk(KERN_ERR "foo bar baz ");
> 	printk("buz\nfiz\n");
> 
> will result in the same as above except for the missing <4> - which means
> "fiz" still ends up at the wrong severity level.
> 
> Confusingly:
> 
> 	printk(KERN_ERR "foo bar baz");
> 	printk(KERN_WARNING "buz\nfiz\n");
> 
> will do as per the original, but is silly.  Wonder how many other places
> are broken by this change.
I wonder if this was intended.  It was introduced in v2.6.31-rc1~324
(printk: clean up handling of log-levels and newlines) by Linus.

Thinking about it I consider the current behaviour more sane, because
I cannot imagine a valid usecase to change the loglevel in a single
printk and having to repeat the same loglevel marker for each newline
isn't very effective, too.  This for example fixes the usage of
pr_warning et al for multiline strings.

Is it worth to add some logic to vprint that handles repeating (or even
changing) markers after a newline?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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