linux-kernel - Re: [RFC] dma-buf: Implement test module

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Message-ID: <20140325180110.GA3532@ravnborg.org>
Date:	Tue, 25 Mar 2014 19:01:10 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	linux-kernel@...r.kernel.org, Michal Marek <mmarek@...e.cz>,
	linux-kbuild@...r.kernel.org
Subject: Re: [RFC] dma-buf: Implement test module

> 
> There are two things that don't work too well with this. First this
> causes the build to break if the build machine doesn't have the new
> public header (include/uapi/linux/dma-buf.h) installed yet. So the only
> way to make this work would be by building the kernel once with SAMPLES
> disabled, install the headers and then build again with SAMPLES enabled.
> Which really isn't very nice.
> 
> One other option that I've tried is to modify the include path so that
> the test program would get the in-tree copy of the public header file,
> but that didn't build properly either because the header files aren't
> properly sanitized and therefore the compiler complains about it
> (include/uapi/linux/types.h).
> 
> One other disadvantage of carrying the sample program in the tree is
> that there's only infrastructure to build programs natively on the build
> machine. That's somewhat unfortunate because if you want to run the test
> program on a different architecture you have to either compile the
> kernel natively on that architecture (which isn't very practical on many
> embedded devices) or cross-compile manually.
> 
> I think a much nicer solution would be to add infrastructure to cross-
> compile these test programs, so that they end up being built for the
> same architecture as the kernel image (i.e. using CROSS_COMPILE).
> 
> Adding Michal and the linux-kbuild mailing list, perhaps this has been
> discussed before, or maybe somebody has a better idea on how to solve
> this.
I actually looked into this some time ago.
May try to dust off the patch.
IIRC the kernel provided headers were used for building - not the one installed on the machine.
And crosscompile were supported.

	Sam
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