linux-kernel - Re: __weak vs ifdef

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Date:	Fri, 25 Jul 2008 05:41:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Adrian Bunk <bunk@...nel.org>,
	Andrea Righi <righi.andrea@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: __weak vs ifdef

On Fri, 25 Jul 2008 06:24:54 -0600 Matthew Wilcox <matthew@....cx> wrote:

> On Fri, Jul 25, 2008 at 02:34:55AM -0700, Andrew Morton wrote:
> > We should make arch_pick_mmap_layout __weak and nuke that ifdef.
> 
> I strongly disagree.  I find it makes it harder to follow code flow
> when __weak functions are involved.  Ifdefs are ugly, no question, but
> they're easier to grep for, see when they'll be defined and know which of
> the arch_pick_mmap_layout() functions will be called.  __weak certainly
> has its uses (eg the sys_ni_syscall is great) but I find it's becoming
> overused.
> 
> My basic point here is that __weak makes the code easier to write but
> harder to read, and we're supposed to be optimising for easier to read.
> 

If you see

void __weak arch_foo(...)

and can't immediately work out what's going on then converting it to an
ifdef maze won't save you.

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