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Date: Wed, 17 Feb 2010 19:07:34 -0700 From: Grant Likely <grant.likely@...retlab.ca> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Matthew Wilcox <matthew@....cx>, Andrew Morton <akpm@...ux-foundation.org>, Adrian Bunk <bunk@...nel.org>, Andrea Righi <righi.andrea@...il.com>, linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: __weak vs ifdef Reaching back into an old discussion.... On Sat, Jul 26, 2008 at 12:38 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote: > > > On Fri, 25 Jul 2008, Matthew Wilcox 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 > > Hell no, they're not. > > Our use of random HAVE_ARCH_xyz or ARCH_SUPPORTS_xyz etc stuff makes > things _totally_ impossible to grep for. > > In contrast, it we did this code as > > #ifndef arch_pick_mmap_layout > void __weak arch_pick_mmap_layout(struct mm_struct *mm) > { > mm->mmap_base = TASK_UNMAPPED_BASE; > mm->get_unmapped_area = arch_get_unmapped_area; > mm->unmap_area = arch_unmap_area; > } > #endif > > then trying to grep for arch_pick_mmap_layout() would show EVERY SINGLE > RELEVANT CASE! And it would show the "__weak" there too, so that once > people get used to this convention, they'd have a really easy time > figuring out the rules from just the output of the 'grep'. [...] Question. If I use this pattern, and use the __weak attribute on core code functions wrapped with a #ifndef, then how does it mesh with EXPORT_SYMBOL*() statements? Do both the core code, and the arch override need to do EXPORT_SYMBOL(), or should EXPORT_SYMBOL() only appear at the core code site? I also assume that at the core code site, the EXPORT_SYMBOL() must appear inside the #ifndef block so that a #define override doesn't break things. Correct? Cheers, g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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