linux-kernel - whose job is it to include various header files?

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Date:	Thu, 13 Mar 2008 18:09:12 -0400 (EDT)
From:	"Robert P. J. Day" <rpjday@...shcourse.ca>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: whose job is it to include various header files?

  more a philosophy question than anything but, while poking around
the percpu stuff today, i noticed in the header file linux/percpu.h
the opening snippet:

 #include <linux/preempt.h>
 #include <linux/slab.h> /* For kmalloc() */
 #include <linux/smp.h>
 #include <linux/string.h> /* For memset() */
 #include <linux/cpumask.h>
 ...

hmmm, i thought to myself (because that's how i refer to myself), i
wonder why this header file is including headers for kmalloc() and
memset() when this header file makes no reference to those routines.
let's see what happens if i remove them and:

  $ make distclean
  $ make defconfig    [x86]
  $ make

... chug chug chug ...

  CC      arch/x86/kernel/nmi_32.o
arch/x86/kernel/nmi_32.c: In function ‘check_nmi_watchdog’:
arch/x86/kernel/nmi_32.c:81: error: implicit declaration of function ‘kmalloc’
arch/x86/kernel/nmi_32.c:81: error: ‘GFP_KERNEL’ undeclared (first use in this function)
arch/x86/kernel/nmi_32.c:81: error: (Each undeclared identifier is reported only once
arch/x86/kernel/nmi_32.c:81: error: for each function it appears in.)
arch/x86/kernel/nmi_32.c:81: warning: assignment makes pointer from integer without a cast
arch/x86/kernel/nmi_32.c:118: error: implicit declaration of function ‘kfree’
make[1]: *** [arch/x86/kernel/nmi_32.o] Error 1
make: *** [arch/x86/kernel] Error 2
$

  ok, now i know.  but that means, of course, that nmi_32.c is
invoking kmalloc() without ever having included the necessary header
file for it -- it's just inheriting that from linux/percpu.h.

  doesn't that (sort of) violate the kernel coding style?  if a file
somewhere needs the contents of some header file, isn't it that file's
responsibility to explicitly include it, and not quietly realize it's
getting it from elsewhere?

rday
--

========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry:
    Have classroom, will lecture.

http://crashcourse.ca                          Waterloo, Ontario, CANADA
========================================================================