Date: Wed, 25 Jun 2008 08:19:13 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Johannes Berg <johannes@sipsolutions.net>
cc: Paul Jackson <pj@sgi.com>, hpa@zytor.com, yhlu.kernel@gmail.com,
       akpm@linux-foundation.org, mingo@elte.hu, tglx@linutronix.de,
       steiner@sgi.com, travis@sgi.com, linux-kernel@vger.kernel.org,
       ying.huang@intel.com, andi@firstfloor.org
Subject: Re: [PATCH 4/5 v2] x86 boot: show pfn addresses in hex not decimal
 in some kernel info printks
In-Reply-To: <1214406026.21847.25.camel@johannes.berg>
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On Wed, 25 Jun 2008, Johannes Berg wrote:
> 
> In networking, we've gone through various incarnations of print_mac()
> which is similar to the sym() macro Paul proposed, and it turned out to
> be undesirable because of the way it interacts with static inlines that
> only optionally contain code at all, the print_mac() function call is
> still emitted by the compiler. People experimented with marking it
> __pure but that had other problems.

You don't even have to go that esoteric.

Just printing things like "sector_t" or "u64" is painful, because the 
exact type depends on config options and/or architecture.

> It would be nice to be able to say
> 
> u8 *eaddr;
> 
> printk(... %M ..., eaddr);

For special things, I do think we should extend the format more, and 
forget about single-character names. It would be lovely to do them as
%[mac], %[u64], %[symbol] or similar. Because once you don't rely on gcc 
checking the string, you can do it.

The problem is that right now we absolutely _do_ rely on gcc checking the 
string, and as such we're forced to use standard patterns, and standard 
patterns _only_. And that means that %M isn't an option, but also that if 
we want symbolic names we'd have to use %p, and not some extension.

But once you drop the 'standard patterns' requirement, I do think you 
should drop it _entirely_, and not just extend it with some pissant 
single-character unreadable mess.

				Linus
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