build: add support code for appending metadata to images

Signed-off-by: Felix Fietkau <nbd@nbd.name>

include/image-commands.mk

@@ -172,3 +172,21 @@ define Build/sysupgrade-tar
 		--rootfs $(call param_get_default,rootfs,$(1),$(IMAGE_ROOTFS)) \
 		$@
 endef
+
+json_quote=$(subst ','\'',$(subst ",\",$(1)))
+#")')
+metadata_devices=$(if $(1),$(subst "$(space)","$(comma)",$(strip $(foreach v,$(1),"$(call json_quote,$(v))"))))
+metadata_json = \
+	'{ $(if $(IMAGE_METADATA),$(IMAGE_METADATA)$(comma)) \
+		"supported_devices":[$(call metadata_devices,$(1))], \
+		"version": { \
+			"dist": "$(call json_quote,$(VERSION_DIST))", \
+			"version": "$(call json_quote,$(VERSION_NUMBER))", \
+			"revision": "$(call json_quote,$(REVISION))", \
+			"board": "$(call json_quote,$(BOARD))" \
+		} \
+	}'
+
+define Build/append-metadata
+	$(if $(SUPPORTED_DEVICES),echo $(call metadata_json,$(SUPPORTED_DEVICES)) | fwtool -I - $@)
+endef

include/image.mk

@@ -346,6 +346,8 @@ define Device/Init
 
   BOARD_NAME :=
   UIMAGE_NAME :=
+  SUPPORTED_DEVICES :=
+  IMAGE_METADATA :=
 
   FILESYSTEMS := $(TARGET_FILESYSTEMS)
 endef
@@ -355,7 +357,8 @@ DEFAULT_DEVICE_VARS := \
   DEVICE_DTS DEVICE_DTS_DIR BOARD_NAME CMDLINE \
   UBOOTENV_IN_UBI KERNEL_IN_UBI \
   BLOCKSIZE PAGESIZE SUBPAGESIZE VID_HDR_OFFSET \
-  UBINIZE_OPTS UIMAGE_NAME UBINIZE_PARTS
+  UBINIZE_OPTS UIMAGE_NAME UBINIZE_PARTS \
+  SUPPORTED_DEVICES IMAGE_METADATA
 
 define Device/ExportVar
   $(1) : $(2):=$$($(2))