linux-kernel - Re: [PATCH resend] video: omap24xxcam: Fix compilation

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Date:	Sat, 19 Feb 2011 17:00:25 +0200
From:	Felipe Balbi <balbi@...com>
To:	David Cohen <dacohen@...il.com>
Cc:	Sakari Ailus <sakari.ailus@...well.research.nokia.com>,
	balbi@...com, Thomas Weber <weber@...science.de>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	linux-omap@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Hans Verkuil <hverkuil@...all.nl>, Tejun Heo <tj@...nel.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH resend] video: omap24xxcam: Fix compilation

Hi,

On Sat, Feb 19, 2011 at 01:35:09PM +0200, David Cohen wrote:
> >> aha, now I get it, so shouldn't the real fix be including <linux/sched.h>
> >> on <linux/wait.h>, I mean, it's <linuux/wait.h> who uses a symbol
> >> defined in <linux/sched.h>, right ?
> 
> That's a tricky situation. linux/sched.h includes indirectly
> linux/completion.h which includes linux/wait.h.

Ok, so the real problem is that there is circular dependency between
<linux/sched.h> and <linux/wait.h>

> By including sched.h in wait.h, the side effect is completion.h will
> then include a blank wait.h file and trigger a compilation error every
> time wait.h is included by any file.

true, but the real problem is the circular dependency between those
files.

> > Surprisingly many other files still don't seem to be affected. But this
> > is actually a better solution (to include sched.h in wait.h).
> 
> It does not affect all files include wait.h because TASK_* macros are
> used with #define statements only. So it has no effect unless some
> file tries to use a macro which used TASK_*. It seems the usual on
> kernel is to include both wait.h and sched.h when necessary.
> IMO your patch is fine.

I have to disagree. The fundamental problem is the circular dependency
between those two files:

sched.h uses wait_queue_head_t defined in wait.h
wait.h uses TASK_* defined in sched.h

So, IMO the real fix would be clear out the circular dependency. Maybe
introducing <linux/task.h> to define those TASK_* symbols and include
that on sched.h and wait.h

Just dig a quick and dirty to try it out and works like a charm

-- 
balbi
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