linux-kernel - Re: kbuild: fixing the select problem

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Date:	Thu, 6 May 2010 19:25:15 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Valdis.Kletnieks@...edu
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	linux-arch@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sam Ravnborg <sam@...nborg.org>, linux-kbuild@...r.kernel.org,
	Randy Dunlap <randy.dunlap@...cle.com>
Subject: Re: kbuild: fixing the select problem

On Thu, May 6, 2010 at 18:47,  <Valdis.Kletnieks@...edu> wrote:
> On Thu, 06 May 2010 09:17:24 EDT, James Bottomley said:
>> On Thu, 2010-05-06 at 08:47 +0200, Geert Uytterhoeven wrote:
>> > On Wed, May 5, 2010 at 23:49, James Bottomley
>> > <James.Bottomley@...senpartnership.com> wrote:
>> > > [Sam: I know you don't maintain kbuild anymore, but since you have the
>> > > most experience, if you could find time to comment, I'd be grateful]
>> > >
>> > > The select problem is that the kbuild select directive will turn a
>> > > symbol on without reference to its dependencies.  This, in turn, means
>> > > that either selected symbols must select their dependencies, or that
>> > > people using select have to be aware of the selected symbol's dependency
>> > > and build those dependencies into their symbol (leading to duplication
>> > > and the possibility of getting the dependencies out of sync).  We use
>> > > select for the scsi transport classes, so we run into this problem in
>> > > SCSI quite a lot.
>> > >
>> > > I think the correct fix is to make a symbol that selects another symbol
>> > > automatically inherit all of the selected symbol's dependencies.
>> >
>> > What if there's a good reason the selected symbol has this dependency?
>> > E.g. it depends on a critical feature not available? Like CONFIG_HAS_IOMEM?
>>
>> I don't quite understand the question.  If a selected symbol has a
>> critical dependency which is config'd to N then the build usually
>> breaks ... that's what I'm calling the select problem.  I thought
>> CONFIG_HAS_IOMEM was usually selected by the architecture, though.  In
>> the new proposal, we wouldn't be able to generate the invalid
>> configuration in the first place.
>
> I think Geert is asking "If the arch says CONFIG_HAS_IOMEM=n, but some driver
> does a 'select CONFIG_FOO' which then (under your proposal) forces the
> value CONFIG_BAR=y, which eventually ends up with CONFIG_HAS_IOMEM=y, what
> should the behavior be?"

Yep, that was my (bogus) question...

> (I suspect the right answer here is "one of the symbols is buggy and its
> 'select' should be a 'depends' instead", but somebody else better double-check
> that conclusion - I'm hardly a Kconfig expert).

No, the CONFIG_FOO will inherit the dependency on CONFIG_HAS_IOMEM.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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