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From: "Luis R. Rodriguez" <lrodriguez@atheros.com>
Date: Mon, 22 Nov 2010 18:32:18 -0800
Message-ID: <AANLkTi=7ErFUgPOFaePh6GUP5rF18c=q5Gs6+GYvMiOK@mail.gmail.com>
Subject: Re: [PATCH 28/44] compat: avoid using `#include_next' directive in
 compat headers
To: Arnaud Lacombe <lacombar@gmail.com>
Cc: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	Luis Rodriguez <Luis.Rodriguez@atheros.com>
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Sender: linux-wireless-owner@vger.kernel.org

On Mon, Nov 22, 2010 at 6:19 PM, Arnaud Lacombe <lacombar@gmail.com> wrote:
> Hi,
>
> On Mon, Nov 22, 2010 at 1:09 PM, Luis R. Rodriguez
> <lrodriguez@atheros.com> wrote:
>> On Sun, Nov 21, 2010 at 5:36 PM, Arnaud Lacombe <lacombar@gmail.com> wrote:
>>> [...]
>>> The compat headers should be at the end of the include list, so that
>>> the kernel headers get included first, and the compat one will only be
>>> when the kernel does not provide the header. This is the only sane way
>>> to override kernel provided stuff. That said, there is certainly a
>>> use-case I missed.
>>
>> Agreed, but you are missing the purpose of the trick used here.
> certainly :)
>
>> The
>> purpose of the include_next was so that we can name our own
>> <linux/pm_qos_params.h> which is part of compat and these directories
>> *will* get a priority over the kernel's so that way we can avoid
>> ifdef'ing all includes for the same file on the upstream code.
> I'm not sure to get what you mean by "we can avoid ifdef'ing all
> includes for the same file on the upstream code", can you details ?

Ah, that's right, you don't see or use compat-wireless likely. Ok, so
what we do for backporting the 802.11 subsystem, Bluetooth and some
Ethernet drivers is we take the stock upstream files, stuff them into
a new directory, and then apply a series of patches to them to get the
files to properly compile. The patches address all things that was not
possible to backport through compat.git. Header file changes is one of
the typical things we run into. If a new header file is added to newer
kernels we can play a hack for older kernels and leave the code intact
and introduce our own include/linux/foo.h through compat by prefering
the local path over the kernel's path. If we're on newer kernels
though include_next will go on the search path and find the kernel's
own header file.

>> Without
>> an include_next we'd simply skip including the kernel's own original
>> header file.
>>
> I admit that I removed that part merely because I went loose on the
> trigger that day. AFAIR, there was no technical point per-se, so I
> would not mind omitting this patch.

OK cool, lets skip that then.

  Luis