Re: [PATCH -next 2/2] kbuild: fix for updated LZ4 tool with thenew streaming format

[Sam Ravnborg]

On Tue, Jul 16, 2013 at 10:08:07AM +0200, Yann E. MORIN wrote:
> Andrew, All,
> 
> On Tuesday 16 July 2013 09:56:11 Andrew Morton wrote:
> > On Tue, 16 Jul 2013 00:47:27 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > On Mon, 15 Jul 2013 15:08:20 -0700 "H. Peter Anvin" <hpa@xxxxxxxxx> wrote:
> > > > On 07/15/2013 03:03 PM, Andrew Morton wrote:
> [--SNIP--]
> > > > We keep running over the need to be able to have kconfig run tests on
> > > > the build system (for toolchain support or for optional tools needed);
> > > > running them in the Makefiles (i.e. at Kbuild time) is simply too late.
> > > > 
> > > 
> > > Would it make sense to extend Kconfig's `depends'?
> > > 
> > > 	depends on $(shell-command)
> > > 
> > > I don't know how practical that would be to implement...
> 
> I'm afraid this will get rather ugly and not trivial.
> 
> Can we mix 'depends on SYMBOL' and 'depends on $(command)' ?
> Can we mix both in a boolean expression such as 'depends on SYMBOL
> && $(command)' ?
> 
> What would be the condition for evaluating the dependency rule? Evaluation
> at Kconfig read-time might not be enough, given this construct:
> 
>     config FOO
>         depends on $(foo)
>     comment "'foo' is missing, please install it"
>         depends on !$(foo)
> 
> Also, I believe Kconfig should stay a config-only language, without
> much esoteric features.

We could extend the symbol option part to retreive values from a binary.
Something like this:

config FOOBAR
        bool
        option exec="true"

FOOBAR would assume the value "y" if the command true has exit code == 0, otherwise "n".
And similar conversions for other types.

This only extendt Kconfig slightly - using an already present method to import
external values.

The drawback I see with this approach is that we may execute a lot of small programs
where the value is never used.
Implementing lazy evaluation of a symbol value will not be easy I think.

	Sam
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