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From: Nicolas Pitre <nico@cam.org>
Subject: Re: [PATCH] index-pack usage of mmap() is unacceptably slower on many
 OSes other than Linux
Date: Tue, 19 Dec 2006 14:14:55 -0500 (EST)
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To: Junio C Hamano <junkio@cox.net>
Sender: git-owner@vger.kernel.org

On Tue, 19 Dec 2006, Junio C Hamano wrote:

> > diff --git a/index-pack.c b/index-pack.c
> > index 6d6c92b..e08a687 100644
> > --- a/index-pack.c
> > +++ b/index-pack.c
> > @@ -1,3 +1,8 @@
> > +#define _XOPEN_SOURCE 500
> > +#include <unistd.h>
> > +#include <sys/time.h>
> > +#include <signal.h>
> > +
> >  #include "cache.h"
> >  #include "delta.h"
> >  #include "pack.h"
> > @@ -6,8 +11,6 @@
> >  #include "commit.h"
> >  #include "tag.h"
> >  #include "tree.h"
> > -#include <sys/time.h>
> > -#include <signal.h>
> 
> Most of the rest of the sources seem to do our includes first
> and source-file specific system includes at the end.  What's the
> rationale for this change?

Because _XOPEN_SOURCE must be defined before including unistd.h 
otherwise pread is not declared and a warning is issued.

> Do we need _XOPEN_SOURCE=500 because pread() is XSI?

The pread man page says Unix98.

> Also nobody other than convert-objects.c has _XOPEN_SOURCE level
> specified.  If _XOPEN_SOURCE matters I wonder if we should do so
> in some central place to make it consistent across source files?

Your call I guess.