From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bruce Richardson <bruce.richardson@intel.com>
Subject: Re: [PATCH v3] mk: filter duplicate configuration entries
Date: Wed, 6 Jul 2016 09:12:38 +0100
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To: Christian Ehrhardt <christian.ehrhardt@canonical.com>
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On Wed, Jul 06, 2016 at 07:37:45AM +0200, Christian Ehrhardt wrote:
> *updates in v3*
> - replace tac with sed '1!G;h;$!d' to avoid build time dependency
> 
> *updates in v2*
> - move to .config target
> - fix usage order of tac
> - simplify inner section by only using awk (instead of awk+loop+bash+sed)
> 
> Due to the hierarchy and the demand to keep the base config showing all
> options, some config keys end up multiple times in the .config file.
> 
> Due to the way the actual config is sourced only the last entry is
> important. That can confuse people changing values in .config which
> are then ignored.
> 
> A suggested solution was to filter for duplicates at the end of the
> actual config step which is implemented here.
> 
> Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
> ---
>  mk/rte.sdkconfig.mk | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/mk/rte.sdkconfig.mk b/mk/rte.sdkconfig.mk
> index a3acfe6..d031bf4 100644
> --- a/mk/rte.sdkconfig.mk
> +++ b/mk/rte.sdkconfig.mk
> @@ -79,11 +79,17 @@ $(RTE_OUTPUT):
>  ifdef NODOTCONF
>  $(RTE_OUTPUT)/.config: ;
>  else
> +# Generate config from template, if there are duplicates keep only the last
>  $(RTE_OUTPUT)/.config: $(RTE_CONFIG_TEMPLATE) FORCE | $(RTE_OUTPUT)
>  	$(Q)if [ "$(RTE_CONFIG_TEMPLATE)" != "" -a -f "$(RTE_CONFIG_TEMPLATE)" ]; then \
>  		$(CPP) -undef -P -x assembler-with-cpp \
>  		-ffreestanding \
>  		-o $(RTE_OUTPUT)/.config_tmp $(RTE_CONFIG_TEMPLATE) ; \
> +		sed '1!G;h;$$!d' $(RTE_OUTPUT)/.config_tmp > $(RTE_OUTPUT)/.config_tmp_reverse ; \
> +		awk --field-separator '=' '!/^#/ {if (!seen[$$1]) {print ($$0)}; seen[$$1]=1;} \
> +			/^#/ {print($$0)}' $(RTE_OUTPUT)/.config_tmp_reverse \
> +			| sed '1!G;h;$$!d' > $(RTE_OUTPUT)/.config_tmp ; \
> +		rm $(RTE_OUTPUT)/.config_tmp_reverse ; \
>  		if ! cmp -s $(RTE_OUTPUT)/.config_tmp $(RTE_OUTPUT)/.config; then \
>  			cp $(RTE_OUTPUT)/.config_tmp $(RTE_OUTPUT)/.config ; \
>  			cp $(RTE_OUTPUT)/.config_tmp $(RTE_OUTPUT)/.config.orig ; \
> -- 

Given the length and complexity of the work being done here, using some pretty
fancy sed and awk features, I feel that the comment at the top should be
expanded to actually explain what is being done and how. I would also include
in that explanation how sed is being used to reverse a file. Personally, I
would have preferred to keep the dependency on tac for a readability perspective.

/Bruce