initramfs to also use merge-rootfs

makefile

@@ -26,6 +26,11 @@ BUILD_BASE_STAMP := $(OUT_DIR)/.build-base-$(TAG).stamp
 
 ALPINE_SERIES := $(word 1,$(subst ., ,$(ALPINE_VER))).$(word 2,$(subst ., ,$(ALPINE_VER)))
 
+BUILD_VERSION   ?= $(KUBE_VERSION)
+BUILD_DATE      := $(shell date -u +%Y-%m-%dT%H:%M:%SZ)
+BUILD_GIT       := $(shell git rev-parse --short HEAD 2>/dev/null || echo unknown)
+BUILD_INFO_FILE := $(OUT_DIR)/build-info
+
 # ---- File groups -------------------------------------------------------------
 
 # Use find so adding new files under these dirs is automatically picked up.
@@ -52,6 +57,7 @@ INITRAMFS_DEPS := \
 	$(BUSYBOX_TAR) \
 	docker/initramfs.Dockerfile \
 	$(INITRAMFS_SRCS) \
+	$(BUILD_INFO_FILE) \
 	build.env \
 	makefile
 
@@ -64,6 +70,7 @@ ITB_DEPS := \
 
 RELEASE_DEPS := \
 	$(BUILD_BASE_STAMP) \
+	$(BUILD_INFO_FILE) \
 	$(BOARD_ITB) \
 	$(ALPINE_TAR) \
 	$(CRIO_TAR) \
@@ -111,6 +118,15 @@ $(CRIO_TAR): | $(PACKAGES_DIR)
 
 # ---- Build stages ------------------------------------------------------------
 
+$(BUILD_INFO_FILE):
+	@mkdir -p $(dir $@)
+	@printf '%s\n' \
+		'export $(BUILD_TAG)_VERSION="$(BUILD_VERSION)"' \
+		'export $(BUILD_TAG)_BUILD_DATE="$(BUILD_DATE)"' \
+		'export $(BUILD_TAG)_GIT="$(BUILD_GIT)"' \
+		'export $(BUILD_TAG)_RELEASE_IMAGE="$(notdir $(RELEASE_IMAGE))"' \
+		> $@
+
 $(BUILD_BASE_STAMP): $(BUILD_BASE_DEPS) | $(OUT_DIR)
 	docker build \
 		-f docker/build-base.Dockerfile \
@@ -138,6 +154,7 @@ $(INITRAMFS): $(INITRAMFS_DEPS) | $(OUT_DIR)
 		--build-arg ARCH=$(ARCH) \
 		--build-arg CROSS_COMPILE=$(CROSS_COMPILE) \
 		--build-arg BUSYBOX_VERSION=$(BUSYBOX_VERSION) \
+		--build-arg BUILD_TAG=$(BUILD_TAG) \
 		--output type=local,dest=./$(OUT_DIR) .
 	test -f $@