Date: Thu, 13 Mar 2008 15:46:31 -0700
From: Randy Dunlap <randy.dunlap@oracle.com>
To: "Robert P. J. Day" <rpjday@crashcourse.ca>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: whose job is it to include various header files?
Message-Id: <20080313154631.ae147130.randy.dunlap@oracle.com>
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On Thu, 13 Mar 2008 18:09:12 -0400 (EDT) Robert P. J. Day wrote:

> 
>   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?

Yes.

---
~Randy
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