On Fri, Feb 07, 2014 at 05:02:02PM -0800, David Rientjes wrote:
> On Fri, 7 Feb 2014, Josh Triplett wrote:
>
> > > Why?? If CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID then, yes, we need it to be
> > > global. Otherwise it's perfectly fine just being static in file scope.
> > > This causes the compilation unit to break when you compile it, not wait
> > > until vmlinux and find undefined references.
> > >
> > > I see no reason it can't be done like this in mm/page_alloc.c:
> > >
> > > #ifdef CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID
> > > extern int __meminit __early_pfn_to_nid(unsigned long pfn);
> >
> > No, a .c file should not have an extern declaration in it. This should
> > live in an appropriate header file, to be included in both page_alloc.c
> > and any arch file that defines an overriding function.
> >
>
> Ok, so you have religious beliefs about extern being used in files ending
> in .c and don't mind the 2900 occurrences of it in the kernel tree and
> desire 14 line obfuscation in header files with comments to what is being
> defined in .c files such as "please see mm/page_alloc.c" as mm.h has.
I (and many others) have very specific technical objections to not
having the same prototype seen by both the definition and use of a
function: that helps keep the prototype in sync with the definition(s),
helps keep all definitions in sync if there are multiple such
definitions, and eliminates -Wmissing-prototype warnings (which in
addition to those benefits also help detect functions that should be
made static or eliminated).
And as mentioned before, those 14 lines can be significantly simplified;
Rashika's patch already does one such simplification.
Those 2900 occurrences should go away as well, and Rashika's previous
patches have already fixed many of them.
> > > Both of these options look much better than
> > >
> > > include/linux/mm.h:
> > >
> > > #if !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) && \
> > > !defined(CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID)
> > > static inline int __early_pfn_to_nid(unsigned long pfn)
> > > {
> > > return 0;
> > > }
> > > #else
> > > /* please see mm/page_alloc.c */
> > > extern int __meminit early_pfn_to_nid(unsigned long pfn);
> > > #ifdef CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID
> > > /* there is a per-arch backend function. */
> > > extern int __meminit __early_pfn_to_nid(unsigned long pfn);
> > > #endif /* CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID */
> > > #endif
> > >
> > > where all this confusion is originating from.
> >
> > The proposal is to first simplify those ifdefs by eliminating the inner
> > one in the #else; I agree with Andrew that we ought to go ahead and take
> > that step given the patch at hand, and then figure out if there's an
> > additional simplification possible.
> >
>
> If additional simplification is possible? Yeah, it's __weak which is
> designed for this purpose.
No objections here if someone wants to write that patch.
- Josh Triplett
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