[Buildroot] [PATCH 2/3] Add support for BR2_EXTERNAL

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Dear Tzu-Jung Lee,

On Fri, 13 Sep 2013 14:43:11 +0800, Tzu-Jung Lee wrote:

> >>   I'm not really convinced by the principle. The external.mk is exactly
> >> the same as the local override .mk; the Config.in appears at the very end
> >> of the top-level menu. Instead, I think we should enforce the buildroot
> >> hierarchy in the external dir, i.e.
> >>
> >> source <path-to-external-dir>/package/Config.in
> >>
> >> at the top of package/Config.in, and
> >>
> >> -include $(sort $(wildcard $(BR2_EXTERNAL)/package/*/*.mk))
> >>
> >> in the top-level Makefile.
> >
> > This is what I had originally done, but it seemed to me that the
> > external stuff may wish to add other Kconfig options than just
> > packages. That said, I've done this BR2_EXTERNAL stuff mainly for
> > packages, so if people think that we should restrict this to packages,
> > I'm fine with that.
> >
> 
> We do want to support the absolute paths for both Config.in and *.mk.
> 
> As a "buildroot overlay", we have similar structures in overlay/ like
> the buildroot/,
> such as configs, fs, packages, etc.
> 
> This requires the buildroot to support only only the *.mk and
> Config.in in the top
> level over overlay/, but also those in their sub directories.
> 
> The *.mk case may be get rid of with Arnount's suggestion.
> But I'm wondering could we solve the Config.in case in a less trickier way?

I am not sure what you mean here. What do you mean by "support the
absolute paths for both Config.in and *.mk" ?

> The overlay/Makefile plays a trick, which allows us to work under overlay/ as we
> work under buildroot/
> 
> Suppose we have the following configs,
> 
>   overlay/configs/foo_defconfig
> 
> Our build sequence will be:
> 
>   $ cd overlay
>   $ make O=../output/foo foo_defconfig
>   $ make O=../output/foo
> 
> With either Thomas's patch or our local patch, other targets supported by
> buildroot, such as menuconfig, help, etc also works under overlay/ as they do
> under buildroot/.
> 
> ##### overlay/Makefile #######
> EXTERNAL_OVERLAY       ?= $(realpath $(dir $(lastword $(MAKEFILE_LIST))))
> export EXTERNAL_OVERLAY
> 
> BUILDROOT_TOP           = ../buildroot
> 
> all:
>         ln -fs ../overlay $(BUILDROOT_TOP)
>         make -C $(BUILDROOT_TOP)
> 
> %:
>         ln -fs ../overlay $(BUILDROOT_TOP)
>         make -C $(BUILDROOT_TOP) $(MAKECMDGOALS)
> 
> ##### overlay/local.mk #######
> -include overlay/package/*/*.mk
> -include overlay/package/*/*/*.mk
> 
> -include overlay/cust/*/*.mk
> -include overlay/cust/*/*/*.mk
> 
> -include overlay/linux/*.mk
> 
> ###### overlay/Config.in ######
> source "overlay/package/Config.in"
> source "overlay/cust/Config.in"
> 
> ###### overlay/package/Config.in ######
> source "overlay/package/xxx/Config.in"

This is what BR2_EXTERNAL allows. Of course, doing a
BR2_EXTERNAL/Makefile that allows to run Buildroot from the external
(overlay) directory is something left for the person who creates the
overlay, I believe.

Best regards,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com