linux-kernel - Re: [patch 2/9] Conditional Calls

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Date:	Fri, 1 Jun 2007 13:49:13 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Andi Kleen <andi@...stfloor.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/9] Conditional Calls - Hash Table

On Fri, Jun 01, 2007 at 02:06:54PM -0400, Mathieu Desnoyers wrote:
> * Andi Kleen (andi@...stfloor.org) wrote:
> > > It's not clear to me why either of those things are necessary. An
> > > example please?
> > 
> > It's certainly possible that a global flag would need to be tested
> > more than once.
> > 
> > I guess it would work if a symbol is associated with a single
> > definition. e.g. if there is a DEFINE_COND_CALL() somewhere
> > and the individual cond calls reference it.
> 
> Yes, but as you have probably understood, I want to have everything
> embedded at the cond_call() site rather than polluting the rest of the
> code with declarations.

And you do so at the expensive of the ability to have compile-time
checks and the need to jump through a hash table at run-time. This
doesn't seem like a good trade-off.

Even if we -don't- do something like DEFINE_COND_CALL, it's still
probably a good idea to not use raw strings inline and to instead use
#defines. Raw strings are only slightly better than magic numbers.

> Also, if we have the same cond_calls in different modules, in which
> module shall it be defined ?

This isn't a new problem. It exists for every other type of object in
the kernel.

-- 
Mathematics is the supreme nostalgia of our time.
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