Allow building generic OTA packages.

We already have targets that build generic system images, which can be
applied (flashed) onto matching devices to replace their target-specific
system images. This CL adds PRODUCT_BUILD_GENERIC_OTA_PACKAGE that
allows building generic OTA packages to be installed over-the-air.

Since A/B and non-A/B OTAs have different package formats, currently the
support is limited to targets that use A/B OTAs. Note that this CL only
allows _building_ the package - will need additional changes for the
actual package install as well as targeting matching devices.

Bug: 122851610
Test: `m otapackage` on a target that sets
      `PRODUCT_BUILD_GENERIC_OTA_PACKAGE := true`.
Test: TreeHugger
Change-Id: If6fd2da15d24c5aaee09618efe94514c6d83292d

core/Makefile

@@ -3445,7 +3445,7 @@ ifeq ($(BUILD_OS),darwin)
   build_ota_package := false
   build_otatools_package := false
 else
-  # set build_ota_package, and allow opt-out below
+  # Set build_ota_package, and allow opt-out below.
   build_ota_package := true
   ifeq ($(TARGET_SKIP_OTA_PACKAGE),true)
     build_ota_package := false
@@ -3456,20 +3456,22 @@ else
   ifeq ($(TARGET_PRODUCT),sdk)
     build_ota_package := false
   endif
-  ifneq ($(filter generic%,$(TARGET_DEVICE)),)
-    build_ota_package := false
-  endif
-  ifeq ($(TARGET_NO_KERNEL),true)
-    build_ota_package := false
-  endif
-  ifeq ($(recovery_fstab),)
-    build_ota_package := false
-  endif
   ifeq ($(TARGET_BUILD_PDK),true)
     build_ota_package := false
   endif
+  ifneq ($(PRODUCT_BUILD_GENERIC_OTA_PACKAGE),true)
+    ifneq ($(filter generic%,$(TARGET_DEVICE)),)
+      build_ota_package := false
+    endif
+    ifeq ($(TARGET_NO_KERNEL),true)
+      build_ota_package := false
+    endif
+    ifeq ($(recovery_fstab),)
+      build_ota_package := false
+    endif
+  endif # PRODUCT_BUILD_GENERIC_OTA_PACKAGE
 
-  # set build_otatools_package, and allow opt-out below
+  # Set build_otatools_package, and allow opt-out below.
   build_otatools_package := true
   ifeq ($(TARGET_SKIP_OTATOOLS_PACKAGE),true)
     build_otatools_package := false
@@ -3925,6 +3927,9 @@ endif
 	$(hide) echo 'mkbootimg_version_args=$(INTERNAL_MKBOOTIMG_VERSION_ARGS)' >> $(zip_root)/META/misc_info.txt
 	$(hide) echo "multistage_support=1" >> $(zip_root)/META/misc_info.txt
 	$(hide) echo "blockimgdiff_versions=3,4" >> $(zip_root)/META/misc_info.txt
+ifeq ($(PRODUCT_BUILD_GENERIC_OTA_PACKAGE),true)
+	$(hide) echo "build_generic_ota_package=true" >> $(zip_root)/META/misc_info.txt
+endif
 ifneq ($(OEM_THUMBPRINT_PROPERTIES),)
 	# OTA scripts are only interested in fingerprint related properties
 	$(hide) echo "oem_fingerprint_properties=$(OEM_THUMBPRINT_PROPERTIES)" >> $(zip_root)/META/misc_info.txt

core/board_config.mk

@@ -475,6 +475,13 @@ ifeq ($(AB_OTA_UPDATER),true)
   endif
 endif
 
+# Sanity check for building generic OTA packages. Currently it only supports A/B OTAs.
+ifeq ($(PRODUCT_BUILD_GENERIC_OTA_PACKAGE),true)
+  ifneq ($(AB_OTA_UPDATER),true)
+    $(error PRODUCT_BUILD_GENERIC_OTA_PACKAGE with 'AB_OTA_UPDATER != true' is not supported)
+  endif
+endif
+
 # Check BOARD_VNDK_VERSION
 define check_vndk_version
   $(eval vndk_path := prebuilts/vndk/v$(1)) \

core/product.mk

@@ -322,6 +322,11 @@ _product_var_list += \
 # set this variable to prevent OTA failures.
 _product_var_list += PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS
 
+# If set to true, this product builds a generic OTA package, which installs generic system images
+# onto matching devices. The product may only build a subset of system images (e.g. only
+# system.img), so devices need to install the package in a system-only OTA manner.
+_product_var_list += PRODUCT_BUILD_GENERIC_OTA_PACKAGE
+
 # Whether any paths are excluded from being set XOM when ENABLE_XOM=true
 _product_var_list += PRODUCT_XOM_EXCLUDE_PATHS
 _product_var_list += PRODUCT_MANIFEST_PACKAGE_NAME_OVERRIDES