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

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Date:	Thu, 06 May 2010 12:47:07 -0400
From:	Valdis.Kletnieks@...edu
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	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, 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?"

(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).

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