linux-kernel - Re: QUERY: Inclusion of header files in kernel header files

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Message-ID: <4B85019E.9040708@ladisch.de>
Date:	Wed, 24 Feb 2010 11:38:22 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Theodore Tso <tytso@....EDU>
CC:	viresh kumar <viresh.linux@...il.com>,
	Borislav Petkov <petkovbb@...glemail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: QUERY: Inclusion of header files in kernel header files

Theodore Tso wrote:
> Also, it's highly desirable that as much as possible multiple
> inclusion is fixed up at the same time you add extra #includes into
> header files.   Protecting against multiple inclusion is critical,
> yes, but even with the protection against multiple inclusion, the
> header file has to get parsed a second time, and that slows down
> kernel compiles.

Multiple inclusion of a protected header does not hurt at all; gcc
detects that a header file uses #ifdef/#endif header guards and
automatically ignores any #include for that file if the symbol is
already defined.


Regards,
Clemens
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