linux-kernel - Re: [RFC][PATCH] printk: Add %pb to print bitmaps

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Message-ID: <1336597121.2527.74.camel@twins>
Date:	Wed, 09 May 2012 22:58:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Igor Mammedov <imammedo@...hat.com>, Jiang Liu <liuj97@...il.com>,
	linux-kernel@...r.kernel.org, mingo@...nel.org, pjt@...gle.com,
	tglx@...utronix.de, seto.hidetoshi@...fujitsu.com,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH] printk: Add %pb to print bitmaps

On Wed, 2012-05-09 at 12:07 -0700, Andrew Morton wrote:
> On Wed, 09 May 2012 15:27:23 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > + * - 'b' For a bitmap, consumes 2 args, second is int
> 
> There's a pretty widespread convention that %b is used to print in
> binary: printf("%b", 10) -> 1010.  Regrettably it isn't part of
> standard C, but it's often supported anyway.  Perl's printf does this
> as well.  Perl uses %B also.
> 
> If we later want to add binary printing to kernel print(), we'd presumably
> use %pb, to match this precedent.

I'd expect something like %ub, %p would take a pointer to a value.

Too bad both %b and %B generate a warning, it would be rather trivial to
add base 2 number stuff.

> So perhaps it would be better to avoid consuming `b' for bitmaps?

With %.*pb not actually working I could use %pC to mean a cpumask and
skip the generic bitmap stuff.
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