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SubjectRe: [git-pull -tip] x86: include inverse Xmas tree patches
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On Sat, 2009-03-28 at 18:58 +0300, Alexey Dobriyan wrote:
> On Sat, Mar 28, 2009 at 03:55:49PM +0000, Alan Cox wrote:
> > > kenel.org/pub/scm/linux/kernel/git/jaswinder/linux-2.6-Xmas.git x86/core
> > > >
> > > > Jaswinder Singh Rajput (49):
> > > > x86: process_32.c include inverse Xmas tree effect
> > >
> > > What the heck is this?
> >
> > Does inverse christmas tree effect not translate well. It could perhaps
> > have been more clearly explained.
> >
> > Getting the includes under control is a good thing and saves everyone
> > time.
>
> Moving #includes up and down is not getting them under control.

Here is Ingo's response about this effect:

On Sun, 2009-03-15 at 05:54 +0100, Ingo Molnar wrote:
> * Li Zefan <lizf@cn.fujitsu.com> wrote:
>
> > > #include <linux/debugfs.h>
> > > #include <linux/uaccess.h>
> > > -#include <linux/stat.h>
> > > +#include <linux/module.h>
> > > #include <linux/init.h>
> > > +#include <linux/stat.h>
> > > #include <linux/io.h>
> > > #include <linux/mm.h>
> > > -#include <linux/module.h>
> > >
> >
> > Just curious about the rule to sort those includes, and why they need
> > to be rearranged.
>
> Such includes (the 'reverse christmas tree'):
>
> #include <linux/interrupt.h>
> #include <linux/mmiotrace.h>
> #include <linux/bootmem.h>
> #include <linux/compiler.h>
> #include <linux/highmem.h>
> #include <linux/kprobes.h>
> #include <linux/uaccess.h>
> #include <linux/vmalloc.h>
> #include <linux/vt_kern.h>
> #include <linux/signal.h>
> #include <linux/kernel.h>
> #include <linux/ptrace.h>
> #include <linux/string.h>
> #include <linux/module.h>
> #include <linux/kdebug.h>
> #include <linux/errno.h>
> #include <linux/magic.h>
> #include <linux/sched.h>
> #include <linux/types.h>
> #include <linux/init.h>
> #include <linux/mman.h>
> #include <linux/tty.h>
> #include <linux/smp.h>
> #include <linux/mm.h>
>
> #include <asm/kmemcheck.h>
> #include <asm/tlbflush.h>
> #include <asm/pgalloc.h>
> #include <asm/segment.h>
> #include <asm/system.h>
> #include <asm/proto.h>
> #include <asm/traps.h>
> #include <asm/desc.h>
>
> are used by x86 architecture code (and some other subsystems) to
> reduce the likelyhood of patch conflicts in commonly modified
> kernel files.
>
> Without such ordering developers typically append to the
> existing list of include files when introducing a new header -
> creating an almost certain patch conflict. Via the above
> ordering, new headers get distributed roughly evenly amongst the
> full range - and thus the chance of patch conflicts is much
> smaller.
>
> This way it also looks a bit more structured and bit less messy.
> It looks unprofessional and sloppy if a .c file starts with a
> big block of thrown-together include files.
>
> Ingo




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