[Buildroot] [PATCH 1/1] Makefile: Support merged defconfigs

[Cyril Bur <cyrilbur@gmail.com>]

On Mon,  9 May 2016 15:22:32 +1000
Sam Bobroff <sam.bobroff@au1.ibm.com> wrote:

> Within the Linux kernel, and several other packages, it's currently
> possible to maintain defconfigs as diffs (fragments) against other
> configs but this is not possible with buildroot itself.
> 
> This patch adds the capability, although using a slightly different
> implementation. Files may be added in the normal config directories
> ($TOPDIR/configs or $BR2_EXTERNAL/configs) with the format
> "xxx_defconfig.merge" that contain, one per line, the files to be
> passed to merge_config.sh to create the matching xxx_defconfig file
> (the first line should contain the base config followed by the
> fragments).  The generated defconfig file is then handled as it would
> normally be.
> 
> Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
> ---
> For a discussion about this from the OP build project, see
> https://github.com/open-power/op-build/issues/457
> 

Hi Sam,

> A couple of things about the implementation:
> 
> * merge_config.sh will only output to a file called ".config" so I've set it up
>   to output directly to $TOPDIR/.config, since that's about to be overwritten
>   anyway, but I don't feel this is particularly nice.
> * It seems strange to pass --defconfig=.config when running conf but I couldn't
>   quickly tell if there was something better to do. Using --oldconfig would
>   pick up .config by default but I don't know if it would then process the file
>   correctly so I went with what seemed safe.

Looks like what you've done will work. I've come to the same conclusion as you
that --oldconfig might actually be a better fit, and by extension
--olddefconfig may be even better moving forward as the fragments age and new
symbols get added.

Then it occurred to me I've had this question before and I had to go look what I
did for linux in arch/powerpc/Makefile and turns out, olddefconfig.

> * I realise that there are now four very similar rules that handle defconfigs.
>   I could look at factoring them but it didn't seem worth the effort and
>   complexity at this point.
> 

I have no doubt there may be a refactored solution in there somewhere but I
don't believe it will be as easy to follow as what currently exists. Currently
it is easy to understand why there are four, what they are trying to achieve,
I'd bet that with any refactoring that clarity will be dulled.

>  Makefile | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index 71735b5..eb80152 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -845,6 +845,16 @@ defconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
>  	@$(COMMON_CONFIG_ENV) BR2_DEFCONFIG=$(BR2_EXTERNAL)/configs/$@ \
>  		$< --defconfig=$(BR2_EXTERNAL)/configs/$@ $(CONFIG_CONFIG_IN)
>  
> +%_defconfig: $(BUILD_DIR)/buildroot-config/conf $(TOPDIR)/configs/%_defconfig.merge outputmakefile
> +	cd $(TOPDIR)/configs && xargs -a $@.merge -x -P 1 $(TOPDIR)/support/kconfig/merge_config.sh -m -O $(TOPDIR)
> +	$(COMMON_CONFIG_ENV) BR2_DEFCONFIG=$(TOPDIR)/.config \
> +		$< --defconfig=$(TOPDIR)/.config $(CONFIG_CONFIG_IN)
> +
> +%_defconfig: $(BUILD_DIR)/buildroot-config/conf $(BR2_EXTERNAL)/configs/%_defconfig.merge outputmakefile
> +	cd $(BR2_EXTERNAL)/configs && xargs -a $@.merge -x -P 1 $(TOPDIR)/support/kconfig/merge_config.sh -m -O $(TOPDIR)
> +	$(COMMON_CONFIG_ENV) BR2_DEFCONFIG=$(TOPDIR)/.config \
> +		$< --defconfig=$(TOPDIR)/.config $(CONFIG_CONFIG_IN)
> +
>  savedefconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
>  	@$(COMMON_CONFIG_ENV) $< \
>  		--savedefconfig=$(if $(DEFCONFIG),$(DEFCONFIG),$(CONFIG_DIR)/defconfig) \