linux-kernel - Re: [RFC PATCH] kbuild: Do not select symbols with unmet dependencies

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Message-Id: <200908121436.58490.arnd@arndb.de>
Date:	Wed, 12 Aug 2009 14:36:58 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	Sam Ravnborg <sam@...nborg.org>
Subject: Re: [RFC PATCH] kbuild: Do not select symbols with unmet dependencies

On Wednesday 12 August 2009, Catalin Marinas wrote:
> The "select" statement in Kconfig files allows the enabling of options
> even if they have unmet direct dependencies (i.e. "depends on" expands
> to "no"). Currently, the "depends on" clauses are used in calculating
> the visibility but they do not affect the reverse dependencies in any
> way.
> 
> The patch introduces additional tracking of the "depends on" statements
> and does not allow selecting an option if its direct dependencies are
> not met, also printing a warning.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> Cc: Sam Ravnborg <sam@...nborg.org>

I guess this will change the behaviour of a number of subsystems,
likely causing unexpected regressions. I think your change
makes sense, but we need to be much more careful.

Can you extract a list of configuration symbols that are
impacted by your patch? A possibly way out could be to annotate
all of them first by changing

---
config FOO
	bool

config BAR
	depends on FOO

config BAZ
	select BAR
---

so that we either get

config BAZ
	select FOO
	select BAR

or alternatively, on a case-by-case basis

config BAZ
	depends on FOO
	select BAR

Once that is in place, all the symbols have a well-defined behaviour
and we can safely apply your patch.

	Arnd <><
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