Date: Mon, 6 Feb 2006 16:58:33 +0530 From: Joseph Koshy <joseph.koshy@gmail.com> To: Tanmay <tanmayinamdar@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: What is '_KERNEL' in the source ? Message-ID: <84dead720602060328o39c8f964h3fcf355930262816@mail.gmail.com> In-Reply-To: <cdc1d1310602060234p1ade9a3dh545c57e0dfc76794@mail.gmail.com> References: <cdc1d1310602060234p1ade9a3dh545c57e0dfc76794@mail.gmail.com>
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> In various kernel source files,i came across '#ifdef _KERNEL'.
> What is '_KERNEL' used for ? In some files _KERNEL is #defined to nothing=
??
> Can anybody please explain this ?
It is used to control the visibility of types and prototypes in system head=
ers.
Kernel builds define _KERNEL, but userland compiles usually do not. Thus a
#include <sys/foo.h> has a different meaning in userland than in the kernel=
.
See: src/sys/conf/{kern.pre,kmod}.mk
A few userland utilities (e.g., fstat) define _KERNEL before including
headers from <sys/*> because they need more knowledge of kernel
data structures than is the norm for userland.
--
FreeBSD Volunteer, http://people.freebsd.org/~jkoshy
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