Makefile: Export PLATFORM as docker build argument

This commit introduces a new build configuration file (autogenerated) that
allows to export build parameters to docker files of packages under pkg/.
So far only the PLATFORM is exported as a build argument, which will allow
packages to take different actions according to the PLATFORM provided
during the build.

Signed-off-by: Renê de Souza Pinto <rene@renesp.com.br>

Makefile

@@ -145,6 +145,7 @@ CURRENT_INSTALLER=$(CURRENT_DIR)/installer
 INSTALLER_FIRMWARE_DIR=$(INSTALLER)/firmware
 CURRENT_FIRMWARE_DIR=$(CURRENT_INSTALLER)/firmware
 UBOOT_IMG=$(INSTALLER_FIRMWARE_DIR)/boot
+BUILDARGS_FILE=build-args.conf
 
 # not every firmware file is used on every architecture
 BIOS_IMG_amd64=$(INSTALLER_FIRMWARE_DIR)/OVMF.fd $(INSTALLER_FIRMWARE_DIR)/OVMF_CODE.fd $(INSTALLER_FIRMWARE_DIR)/OVMF_VARS.fd
@@ -313,6 +314,7 @@ LINUXKIT_VERSION=v1.5.2
 LINUXKIT_SOURCE=https://github.com/linuxkit/linuxkit
 LINUXKIT_OPTS=$(if $(strip $(EVE_HASH)),--hash) $(EVE_HASH) $(if $(strip $(EVE_REL)),--release) $(EVE_REL)
 LINUXKIT_PKG_TARGET=build
+LINUXKIT_BUILD_ARGS=--build-arg-file $(BUILDARGS_FILE)
 
 ifdef LIVE_FAST
 # Check the makerootfs.sh and the linuxkit tool invocation, the --input-tar
@@ -431,7 +433,7 @@ currentversion:
 	#echo $(shell readlink $(CURRENT) | sed -E 's/rootfs-(.*)\.[^.]*$/\1/')
 	@cat $(CURRENT_DIR)/installer/eve_version
 
-.PHONY: currentversion linuxkit pkg/kernel
+.PHONY: currentversion linuxkit pkg/kernel $(BUILDARGS_FILE)
 
 test: $(LINUXKIT) test-images-patches | $(DIST)
 	@echo Running tests on $(GOMODULE)
@@ -455,7 +457,7 @@ pillar-%: $(GOBUILDER) | $(DIST)
 	$(QUIET): $@: Succeeded
 
 clean:
-	rm -rf $(DIST) images/out pkg-deps.mk
+	rm -rf $(DIST) $(BUILDARGS_FILE) images/out pkg-deps.mk
 
 $(DOCKERFILE_FROM_CHECKER): $(DOCKERFILE_FROM_CHECKER_DIR)/*.go $(DOCKERFILE_FROM_CHECKER_DIR)/go.*
 	make -C $(DOCKERFILE_FROM_CHECKER_DIR)
@@ -1003,6 +1005,9 @@ else
 	$(QUIET): $@: Succeeded
 endif
 
+$(BUILDARGS_FILE):
+	@echo "PLATFORM=$(PLATFORM)" > $@
+
 %.yml: %.yml.in $(RESCAN_DEPS) | build-tools
 	$(QUIET)$(PARSE_PKGS) $< > $@
 	$(QUIET): $@: Succeeded
@@ -1024,13 +1029,13 @@ get_pkg_build_rstats_yml = $(if $(wildcard pkg/$1/build-rstats.yml),build-rstats
 get_pkg_build_kubevirt_yml = $(if $(and $(filter y,$(DEV)),$(wildcard pkg/$1/build-kubevirt-dev.yml)),build-kubevirt-dev.yml, \
                              $(if $(wildcard pkg/$1/build-kubevirt.yml),build-kubevirt.yml,build.yml))
 
-eve-%: pkg/%/Dockerfile build-tools $(RESCAN_DEPS)
+eve-%: pkg/%/Dockerfile build-tools $(BUILDARGS_FILE) $(RESCAN_DEPS)
 	$(QUIET): "$@: Begin: LINUXKIT_PKG_TARGET=$(LINUXKIT_PKG_TARGET)"
 	$(eval LINUXKIT_DOCKER_LOAD := $(if $(filter $(PKGS_DOCKER_LOAD),$*),--docker,))
 	$(eval LINUXKIT_BUILD_PLATFORMS_LIST := $(call uniq,linux/$(ZARCH) $(if $(filter $(PKGS_HOSTARCH),$*),linux/$(HOSTARCH),)))
 	$(eval LINUXKIT_BUILD_PLATFORMS := --platforms $(subst $(space),$(comma),$(strip $(LINUXKIT_BUILD_PLATFORMS_LIST))))
 	$(eval LINUXKIT_FLAGS := $(if $(filter manifest,$(LINUXKIT_PKG_TARGET)),,$(FORCE_BUILD) $(LINUXKIT_DOCKER_LOAD) $(LINUXKIT_BUILD_PLATFORMS)))
-	$(QUIET)$(LINUXKIT) $(DASH_V) pkg $(LINUXKIT_PKG_TARGET) $(LINUXKIT_OPTS) $(LINUXKIT_FLAGS) --build-yml $(call get_pkg_build_yml,$*) pkg/$*
+	$(QUIET)$(LINUXKIT) $(DASH_V) pkg $(LINUXKIT_PKG_TARGET) $(LINUXKIT_BUILD_ARGS) $(LINUXKIT_OPTS) $(LINUXKIT_FLAGS) --build-yml $(call get_pkg_build_yml,$*) pkg/$*
 	$(QUIET)if [ -n "$(PRUNE)" ]; then \
 		$(LINUXKIT) pkg builder prune; \
 		docker image prune -f; \