Android system & system_ext & product等分区中的build.prop文件是怎么生成的？

Android system & system_ext & product等分区中的build.prop文件是怎么生成的？

# http://aospxref.com/android-13.0.0_r3/xref/build/make/core/sysprop.mk

# http://aospxref.com/android-13.0.0_r3/xref/build/make/tools/buildinfo.sh

buildinfo.sh 脚本内容：

#!/bin/bash

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

# The ro.build.id will be set dynamically by init, by appending the unique vbmeta digest.
if [ "$BOARD_USE_VBMETA_DIGTEST_IN_FINGERPRINT" = "true" ] ; then
  echo "ro.build.legacy.id=$BUILD_ID"
else
  echo "ro.build.id=$BUILD_ID"
fi
echo "ro.build.display.id=$BUILD_DISPLAY_ID"
echo "ro.build.version.incremental=$BUILD_NUMBER"
echo "ro.build.version.sdk=$PLATFORM_SDK_VERSION"
echo "ro.build.version.preview_sdk=$PLATFORM_PREVIEW_SDK_VERSION"
echo "ro.build.version.preview_sdk_fingerprint=$PLATFORM_PREVIEW_SDK_FINGERPRINT"
echo "ro.build.version.codename=$PLATFORM_VERSION_CODENAME"
echo "ro.build.version.all_codenames=$PLATFORM_VERSION_ALL_CODENAMES"
echo "ro.build.version.known_codenames=$PLATFORM_VERSION_KNOWN_CODENAMES"
echo "ro.build.version.release=$PLATFORM_VERSION_LAST_STABLE"
echo "ro.build.version.release_or_codename=$PLATFORM_VERSION"
echo "ro.build.version.release_or_preview_display=$PLATFORM_DISPLAY_VERSION"
echo "ro.build.version.security_patch=$PLATFORM_SECURITY_PATCH"
echo "ro.build.version.base_os=$PLATFORM_BASE_OS"
echo "ro.build.version.min_supported_target_sdk=$PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION"
echo "ro.build.date=`$DATE`"
echo "ro.build.date.utc=`$DATE +%s`"
echo "ro.build.type=$TARGET_BUILD_TYPE"
echo "ro.build.user=$BUILD_USERNAME"
echo "ro.build.host=$BUILD_HOSTNAME"
echo "ro.build.tags=$BUILD_VERSION_TAGS"
echo "ro.build.flavor=$TARGET_BUILD_FLAVOR"
if [ -n "$BOARD_BUILD_SYSTEM_ROOT_IMAGE" ] ; then
  echo "ro.build.system_root_image=$BOARD_BUILD_SYSTEM_ROOT_IMAGE"
fi

# These values are deprecated, use "ro.product.cpu.abilist"
# instead (see below).
echo "# ro.product.cpu.abi and ro.product.cpu.abi2 are obsolete,"
echo "# use ro.product.cpu.abilist instead."
echo "ro.product.cpu.abi=$TARGET_CPU_ABI"
if [ -n "$TARGET_CPU_ABI2" ] ; then
  echo "ro.product.cpu.abi2=$TARGET_CPU_ABI2"
fi

if [ -n "$PRODUCT_DEFAULT_LOCALE" ] ; then
  echo "ro.product.locale=$PRODUCT_DEFAULT_LOCALE"
fi
echo "ro.wifi.channels=$PRODUCT_DEFAULT_WIFI_CHANNELS"

echo "# ro.build.product is obsolete; use ro.product.device"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

echo "# Do not try to parse description or thumbprint"
echo "ro.build.description=$PRIVATE_BUILD_DESC"
if [ -n "$BUILD_THUMBPRINT" ] ; then
  echo "ro.build.thumbprint=$BUILD_THUMBPRINT"
fi

echo "# end build properties"

小结：通过shell脚本的echo语句，将 ro 等属性及属性值 写入 build.prop文件

# http://aospxref.com/android-13.0.0_r3/xref/build/make/core/sysprop.mk

# build.prop文件支持加入import语句，Import 语句指向的文件路径可以通过动态拼接ro属性来组成，可以利用这个特点，实现同一个软件版本定制多个区域的不同属性配置(即：多个区域实现共软体)

system/build.prop：

build.prop文件支持加入import语句，import语句语法：import  另外一个prop文件的绝对路径

另外一个prop文件的绝对路径又可以通过动态的ro属性拼接而成，这样便可以实现开机时根据不同区域加载不同的prop文件