build: create JSON files containing image info

The JSON info files contain details about the created firmware images
per device and are stored next to the created images.

The JSON files are stored as "$(IMAGE_PREFIX).json" and contain some
device/image meta data as well as a list of created firmware images.

An example of openwrt-ramips-rt305x-aztech_hw550-3g.json

    {
      "id": "aztech_hw550-3g",
      "image_prefix": "openwrt-ramips-rt305x-aztech_hw550-3g",
      "images": [
        {
          "name": "openwrt-ramips-rt305x-aztech_hw550-3g-squashfs-sysupgrade.bin",
          "sha256": "db2b34b0ec4a83d9bf612cf66fab0dc3722b191cb9bedf111e5627a4298baf20",
          "type": "sysupgrade"
        }
      ],
      "metadata_version": 1,
      "supported_devices": [
        "aztech,hw550-3g",
        "hw550-3g"
      ],
      "target": "ramips/rt305x",
      "titles": [
        {
          "model": "HW550-3G",
          "vendor": "Aztech"
        },
        {
          "model": "ALL0239-3G",
          "vendor": "Allnet"
        }
      ],
      "version_commit": "r10920+123-0cc87b3bac",
      "version_number": "SNAPSHOT"
    }

Signed-off-by: Paul Spooren <mail@aparcar.org>
(backported from commit 881ed09ee6e23f6c224184bb7493253c4624fb9f)
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

config/Config-build.in

@@ -7,6 +7,13 @@
 
 menu "Global build settings"
 
+	config JSON_ADD_IMAGE_INFO
+		bool "Create JSON info files per build image"
+		default BUILDBOT
+		help
+		  The JSON info files contain information about the device and
+		  build images, stored next to the firmware images.
+
 	config ALL_NONSHARED
 		bool "Select all target specific packages by default"
 		select ALL_KMODS

include/image.mk

@@ -524,7 +524,20 @@ define Device/Build/image
 
   $(BIN_DIR)/$(call IMAGE_NAME,$(1),$(2)): $(KDIR)/tmp/$(call IMAGE_NAME,$(1),$(2))
 	cp $$^ $$@
-
+	$(if $(CONFIG_JSON_ADD_IMAGE_INFO), \
+		DEVICE_ID="$(DEVICE_NAME)" \
+		BIN_DIR="$(BIN_DIR)" \
+		IMAGE_NAME="$(IMAGE_NAME)" \
+		IMAGE_TYPE=$(word 1,$(subst ., ,$(2))) \
+		IMAGE_PREFIX="$(IMAGE_PREFIX)" \
+		DEVICE_TITLE="$(DEVICE_TITLE)" \
+		TARGET="$(BOARD)" \
+		SUBTARGET="$(SUBTARGET)" \
+		VERSION_NUMBER="$(VERSION_NUMBER)" \
+		VERSION_CODE="$(VERSION_CODE)" \
+		SUPPORTED_DEVICES="$(SUPPORTED_DEVICES)" \
+		$(TOPDIR)/scripts/json_add_image_info.py \
+	)
 endef
 
 define Device/Build/artifact
@@ -542,6 +555,8 @@ define Device/Build/artifact
 endef
 
 define Device/Build
+  $(shell rm -f $(BIN_DIR)/$(IMG_PREFIX)-$(1).json)
+
   $(if $(CONFIG_TARGET_ROOTFS_INITRAMFS),$(call Device/Build/initramfs,$(1)))
   $(call Device/Build/kernel,$(1))
 

scripts/json_add_image_info.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+
+import json
+import os
+import hashlib
+
+
+def e(variable, default=None):
+    return os.environ.get(variable, default)
+
+
+json_path = "{}{}{}.json".format(e("BIN_DIR"), os.sep, e("IMAGE_PREFIX"))
+
+with open(os.path.join(e("BIN_DIR"), e("IMAGE_NAME")), "rb") as image_file:
+    image_hash = hashlib.sha256(image_file.read()).hexdigest()
+
+
+def get_titles():
+    return [{"title": e("DEVICE_TITLE")}]
+
+
+if not os.path.exists(json_path):
+    device_info = {
+        "id": e("DEVICE_ID"),
+        "image_prefix": e("IMAGE_PREFIX"),
+        "images": [],
+        "metadata_version": 1,
+        "supported_devices": e("SUPPORTED_DEVICES").split(),
+        "target": "{}/{}".format(e("TARGET"), e("SUBTARGET", "generic")),
+        "titles": get_titles(),
+        "version_commit": e("VERSION_CODE"),
+        "version_number": e("VERSION_NUMBER"),
+    }
+else:
+    with open(json_path, "r") as json_file:
+        device_info = json.load(json_file)
+
+image_info = {"type": e("IMAGE_TYPE"), "name": e("IMAGE_NAME"), "sha256": image_hash}
+device_info["images"].append(image_info)
+
+with open(json_path, "w") as json_file:
+    json.dump(device_info, json_file, sort_keys=True, indent="  ")