Android——build.prop 解析

一.概念

           在Android设备shell终端可以看到/system目录下的build.prop文件，Android的build.prop文件是在Android编译时刻收集的各种property（LCD density/语言/编译时间, etc.），编译完成之后，文件生成在out/target/product/<board>/system/目录下。在Android运行时刻可以通过property_get()[c/c++域] / SystemProperties_get*()[Java域]读取这些属性值，参考Android——SystemProperties的应用

 二.生成

build.prop的生成是由make系统解析build/core/Makefile完成 ：

BUILDINFO_SH := build/tools/buildinfo.sh
$(INSTALLED_BUILD_PROP_TARGET): $(BUILDINFO_SH) $(INTERNAL_BUILD_ID_MAKEFILE) $(BUILD_SYSTEM)/version_defaults.mk $(wildcard $(TARGET_DEVICE_DIR)/system.prop)
	@echo Target buildinfo: $@
	@mkdir -p $(dir $@)
	$(hide) TARGET_BUILD_TYPE="$(TARGET_BUILD_VARIANT)" \
			TARGET_DEVICE="$(TARGET_DEVICE)" \
			PRODUCT_NAME="$(TARGET_PRODUCT)" \
			PRODUCT_BRAND="$(PRODUCT_BRAND)" \
			PRODUCT_DEFAULT_LANGUAGE="$(call default-locale-language,$(PRODUCT_LOCALES))" \
			PRODUCT_DEFAULT_REGION="$(call default-locale-region,$(PRODUCT_LOCALES))" \
			PRODUCT_DEFAULT_WIFI_CHANNELS="$(PRODUCT_DEFAULT_WIFI_CHANNELS)" \
			PRODUCT_MODEL="$(PRODUCT_MODEL)" \
			PRODUCT_MANUFACTURER="$(PRODUCT_MANUFACTURER)" \
			PRIVATE_BUILD_DESC="$(PRIVATE_BUILD_DESC)" \
			BUILD_ID="$(BUILD_ID)" \
			BUILD_DISPLAY_ID="$(BUILD_DISPLAY_ID)" \
			BUILD_NUMBER="$(BUILD_NUMBER)" \
			PLATFORM_VERSION="$(PLATFORM_VERSION)" \
			PLATFORM_SDK_VERSION="$(PLATFORM_SDK_VERSION)" \
			PLATFORM_VERSION_CODENAME="$(PLATFORM_VERSION_CODENAME)" \
			BUILD_VERSION_TAGS="$(BUILD_VERSION_TAGS)" \
			TARGET_BOOTLOADER_BOARD_NAME="$(TARGET_BOOTLOADER_BOARD_NAME)" \
			BUILD_FINGERPRINT="$(BUILD_FINGERPRINT)" \
			TARGET_BOARD_PLATFORM="$(TARGET_BOARD_PLATFORM)" \
			TARGET_CPU_ABI="$(TARGET_CPU_ABI)" \
			TARGET_CPU_ABI2="$(TARGET_CPU_ABI2)" \
			TARGET_AAPT_CHARACTERISTICS="$(TARGET_AAPT_CHARACTERISTICS)" \
	        bash $(BUILDINFO_SH) > $@
	$(hide) if [ -f $(TARGET_DEVICE_DIR)/system.prop ]; then \
	          cat $(TARGET_DEVICE_DIR)/system.prop >> $@; \
	        fi
	$(if $(ADDITIONAL_BUILD_PROPERTIES), \
		$(hide) echo >> $@; \
		        echo "#" >> $@; \
		        echo "# ADDITIONAL_BUILD_PROPERTIES" >> $@; \
		        echo "#" >> $@; )
	$(hide) $(foreach line,$(ADDITIONAL_BUILD_PROPERTIES), \
		echo "$(line)" >> $@;)
	$(hide) build/tools/post_process_props.py $@

build_desc :=

1.目标INSTALLED_BUILD_PROP_TARGET就是

INSTALLED_BUILD_PROP_TARGET := $(TARGET_OUT)/build.prop

可以看到定义一些变量的值比如PRODUCT_DEFAULT_LANGUAGE，会在后面脚本中用到。然后调用build/tools/buildinfo.sh这个脚本

bash $(BUILDINFO_SH) > $@

将变量输出到build.prop当中：

echo "# begin build properties"
echo "# autogenerated by buildinfo.sh"

echo "ro.build.id=$BUILD_ID"
echo "ro.build.display.id=$BUILD_DISPLAY_ID"
echo "ro.build.version.incremental=$BUILD_NUMBER"
echo "ro.build.version.sdk=$PLATFORM_SDK_VERSION"
echo "ro.build.version.codename=$PLATFORM_VERSION_CODENAME"
echo "ro.build.version.release=$PLATFORM_VERSION"
echo "ro.build.date=`date`"
echo "ro.build.date.utc=`date +%s`"
echo "ro.build.type=$TARGET_BUILD_TYPE"
echo "ro.build.user=$USER"
echo "ro.build.host=`hostname`"
echo "ro.build.tags=$BUILD_VERSION_TAGS"
echo "ro.product.model=$PRODUCT_MODEL"
echo "ro.product.brand=$PRODUCT_BRAND"
echo "ro.product.name=$PRODUCT_NAME"
echo "ro.product.device=$TARGET_DEVICE"
echo "ro.product.board=$TARGET_BOOTLOADER_BOARD_NAME"
echo "ro.product.cpu.abi=$TARGET_CPU_ABI"
if [ -n "$TARGET_CPU_ABI2" ] ; then
  echo "ro.product.cpu.abi2=$TARGET_CPU_ABI2"
fi
echo "ro.product.manufacturer=$PRODUCT_MANUFACTURER"
if [ -n "$PRODUCT_DEFAULT_LANGUAGE" ] ; then
  echo "ro.product.locale.language=$PRODUCT_DEFAULT_LANGUAGE"
fi
if [ -n "$PRODUCT_DEFAULT_REGION" ] ; then
  echo "ro.product.locale.region=$PRODUCT_DEFAULT_REGION"
fi
echo "ro.wifi.channels=$PRODUCT_DEFAULT_WIFI_CHANNELS"
echo "ro.board.platform=$TARGET_BOARD_PLATFORM"

echo "# ro.build.product is obsolete; use ro.product.device"
echo "ro.build.product=$TARGET_DEVICE"

echo "# Do not try to parse ro.build.description or .fingerprint"
echo "ro.build.description=$PRIVATE_BUILD_DESC"
echo "ro.build.fingerprint=$BUILD_FINGERPRINT"
echo "ro.build.characteristics=$TARGET_AAPT_CHARACTERISTICS"

echo "# end build properties"

buildinfo.sh脚本完了之后，会把$(TARGET_DEVICE_DIR)/system.prop的内容和

# Add the product-defined properties to the build properties.ADDITIONAL_BUILD_PROPERTIES := \    $(ADDITIONAL_BUILD_PROPERTIES) \    $(PRODUCT_PROPERTY_OVERRIDES)

ADDITIONAL_BUILD_PROPERTIES的属性 追加到build.prop。

至此，生成build.prop完毕！

三.属性