需求背景
目前Google已经释放Android 13的基线代码，其中包括了automotive的product，但芯片厂商针对automotive的Android 13基线并未释放，在释放前，下面的方案商无法得知芯片厂商的将会以哪个product来释放automotive基线，因此，需要提前预研在其他product上移植automotive功能。
相关概念
-
automotive
翻译过来就是汽车的意思，它是基于Android平台的车载信息娱乐系统，简称IVI(In-Vehicle Infotainment)，在Android 13中，automotive长这样
-
product
AOSP针对不同的设备，设置的不同的产品。我们在编译源码时，执行
lunch命令后展示的列表就是当前基线提供的所有productshellq@jason-OptiPlex-7080:/projects/AOSP_Android13$ source build/envsetup.sh q@jason-OptiPlex-7080:/projects/AOSP_Android13$ lunch You're building on Linux Lunch menu .. Here are the common combinations: 1. aosp_arm-eng 2. aosp_arm64-eng 3. aosp_barbet-userdebug 4. aosp_bluejay-userdebug 5. aosp_bluejay_car-userdebug 6. aosp_bramble-userdebug 7. aosp_bramble_car-userdebug 8. aosp_car_arm-userdebug 9. aosp_car_arm64-userdebug 10. aosp_car_x86-userdebug 11. aosp_car_x86_64-userdebug 12. aosp_cf_arm64_auto-userdebug 13. aosp_cf_arm64_phone-userdebug 14. aosp_cf_x86_64_foldable-userdebug 15. aosp_cf_x86_64_pc-userdebug 16. aosp_cf_x86_64_phone-userdebug 17. aosp_cf_x86_64_tv-userdebug 18. aosp_cf_x86_auto-userdebug 19. aosp_cf_x86_phone-userdebug 20. aosp_cf_x86_tv-userdebug 21. aosp_cheetah-userdebug 22. aosp_cloudripper-userdebug 23. aosp_coral-userdebug 24. aosp_coral_car-userdebug 25. aosp_flame-userdebug 26. aosp_flame_car-userdebug 27. aosp_oriole-userdebug 28. aosp_oriole_car-userdebug 29. aosp_panther-userdebug 30. aosp_raven-userdebug 31. aosp_raven_car-userdebug 32. aosp_ravenclaw-userdebug 33. aosp_redfin-userdebug 34. aosp_redfin_car-userdebug 35. aosp_redfin_vf-userdebug 36. aosp_rice14-userdebug 37. aosp_slider-userdebug 38. aosp_sunfish-userdebug 39. aosp_sunfish_car-userdebug 40. aosp_trout_arm64-userdebug 41. aosp_trout_x86-userdebug 42. aosp_whitefin-userdebug 43. aosp_x86-eng 44. aosp_x86_64-eng 45. arm_krait-eng 46. arm_v7_v8-eng 47. armv8-eng 48. armv8_cortex_a55-eng 49. armv8_kryo385-eng 50. beagle_x15-userdebug 51. beagle_x15_auto-userdebug 52. car_ui_portrait-userdebug 53. car_x86_64-userdebug 54. db845c-userdebug 55. gsi_car_arm64-userdebug 56. gsi_car_x86_64-userdebug 57. hikey-userdebug 58. hikey64_only-userdebug 59. hikey960-userdebug 60. hikey960_tv-userdebug 61. hikey_tv-userdebug 62. poplar-eng 63. poplar-user 64. poplar-userdebug 65. qemu_trusty_arm64-userdebug 66. rb5-userdebug 67. sdk_car_arm-userdebug 68. sdk_car_arm64-userdebug 69. sdk_car_portrait_x86_64-userdebug 70. sdk_car_x86-userdebug 71. sdk_car_x86_64-userdebug 72. sdk_pc_x86_64-userdebug 73. silvermont-eng 74. uml-userdebug 75. yukawa-userdebug 76. yukawa_sei510-userdebug Which would you like? [aosp_arm-eng] Pick from common choices above (e.g. 13) or specify your own (e.g. aosp_barbet-eng):不同的product打包出来的镜像略有不同，最后在设备上展示的效果也不一样，比如，手机刷的镜像跟车载刷的镜像，Launcher，Settings等不尽相同。在上面lunch的product列表中，带有car标识的都是automotive product，其他的大部分是phone product。
-
automotive移植
就是将automotive的功能移植到非automotive的product上，即将非automotive product改造成automotive product，本篇我们将
72. sdk_pc_x86_64-userdebug改造成71. sdk_car_x86_64-userdebug，72. sdk_pc_x86_64-userdebug长这样
现在我们要将它改造成上面automotive的样子
product编译配置
每个product的编译离不开四个文件：
AndroidProducts.mk：定义product的名字，以及对应的Makefile文件product.mk：对应product的Makefile文件，比如sdk_pc_x86_64.mk，里面包含了product所有的软件配置BoardConfig.mk：对应product的硬件配置信息device.mk：芯片厂商自定义的硬件配置信息
看一下我们要改造的72. sdk_pc_x86_64-userdebug这四个文件的内容
makefile
#AndroidProducts.mk
PRODUCT_MAKEFILES := \
$(LOCAL_DIR)/sdk_pc_x86_64.mk \
COMMON_LUNCH_CHOICES := \
sdk_pc_x86_64-userdebug \COMMON_LUNCH_CHOICES定义了lunch combo名称为sdk_pc_x86_64-userdebug，该名称包括产品名+构建模式，userdebug表示调试模式，此外还有user模式和eng模式，关于这三个模式的区别，这里不做过多介绍，可自行查阅相关资料。PRODUCT_MAKEFILES指定了product的makefile文件，$(LOCAL_DIR)表示当前目录。
makefile
#sdk_pc_x86_64.mk
PRODUCT_COPY_FILES += device/generic/goldfish/pc/config.ini.pc:config.ini
$(call inherit-product, $(SRC_TARGET_DIR)/product/sdk_x86_64.mk)
PRODUCT_NAME := sdk_pc_x86_64
PRODUCT_DEVICE := emulator64_x86_64
PRODUCT_BRAND := Android
PRODUCT_MODEL := PC on x86_64 emulator
PRODUCT_PACKAGE_OVERLAYS := device/generic/goldfish/pc/overlay
PRODUCT_COPY_FILES += \
device/generic/goldfish/pc/data/etc/pc.xml:$(TARGET_COPY_OUT_VENDOR)/etc/permissions/pc.xml
PRODUCT_SDK_ADDON_SYS_IMG_SOURCE_PROP := device/generic/goldfish/pc/images_source.prop_templatesdk_pc_x86_64.mk文件里定义了产品的name、device硬件配置、brand、model等信息，其中PRODUCT_DEVICE指向BoardConfig.mk和device.mk的父目录
$(call inherit-product, $(SRC_TARGET_DIR)/product/sdk_x86_64.mk)表示该文件继承自sdk_x86_64.mk，$(SRC_TARGET_DIR)指向build/target目录。
PRODUCT_COPY_FILES表示将源码中的文件复制到镜像分区中
makefile
#BoardConfig.mk
# x86_64 emulator specific definitions
TARGET_CPU_ABI := x86_64
TARGET_ARCH := x86_64
TARGET_ARCH_VARIANT := x86_64
TARGET_2ND_ARCH_VARIANT := x86_64
BOARD_DO_NOT_STRIP_VENDOR_MODULES := true
TARGET_PRELINK_MODULE := false
include build/make/target/board/BoardConfigGsiCommon.mk
include build/make/target/board/BoardConfigEmuCommon.mk
BOARD_USERDATAIMAGE_PARTITION_SIZE := 576716800
BOARD_SEPOLICY_DIRS += device/generic/goldfish/sepolicy/x86
# Wifi.
BOARD_WLAN_DEVICE := emulator
BOARD_HOSTAPD_DRIVER := NL80211
BOARD_WPA_SUPPLICANT_DRIVER := NL80211
BOARD_HOSTAPD_PRIVATE_LIB := lib_driver_cmd_simulated
BOARD_WPA_SUPPLICANT_PRIVATE_LIB := lib_driver_cmd_simulated
WPA_SUPPLICANT_VERSION := VER_0_8_X
WIFI_DRIVER_FW_PATH_PARAM := "/dev/null"
WIFI_DRIVER_FW_PATH_STA := "/dev/null"
WIFI_DRIVER_FW_PATH_AP := "/dev/null"BoardConfig.mk中定义了cpu的参数，wifi配置，并且通过include引用了BoardConfigGsiCommon.mk和BoardConfigEmuCommon.mk文件里的配置，前者用于通用系统映像的配置，后者用于模拟器的配置。
device.mk是芯片厂商自定义的配置，这里我们看的是原生代码，分析此文件没啥意义。
上述是72. sdk_pc_x86_64-userdebug的编译配置文件，同理可析71. sdk_car_x86_64-userdebug
product编译流程
当我们执行source build/envsetup.sh命令时，会将envsetup.sh文件中定义的函数加载到当前shell环境，建立shell命令，比如lunch、make、croot等。
当执行lunch命令时，会执行envsetup.sh中的lunch()函数
shell
function lunch()
{
# 定义局部变量`answer`来存放用户通过`lunch`命令传进来的参数（即`lunch-combo`，可以是字符串或数字）
local answer
if [[ $# -gt 1 ]]; then
echo "usage: lunch [target]" >&2
return 1
fi
local used_lunch_menu=0
if [ "$1" ]; then
answer=$1
else
# 如果用户没有没有传进来任何值，则打印出`lunch-combo`列表，提示用户输入
print_lunch_menu
echo "Which would you like? [aosp_arm-eng]"
echo -n "Pick from common choices above (e.g. 13) or specify your own (e.g. aosp_barbet-eng): "
read answer
used_lunch_menu=1
fi
local selection=
if [ -z "$answer" ]
then
#如果用户没有选择，则默认选择为aosp_arm-eng
selection=aosp_arm-eng
elif (echo -n $answer | grep -q -e "^[0-9][0-9]*$")
then
local choices=($(TARGET_BUILD_APPS= get_build_var COMMON_LUNCH_CHOICES))
if [ $answer -le ${#choices[@]} ]
then
# array in zsh starts from 1 instead of 0.
if [ -n "$ZSH_VERSION" ]
then
selection=${choices[$(($answer))]}
else
selection=${choices[$(($answer-1))]}
fi
fi
else
selection=$answer
fi
#省略部分代码
TARGET_PRODUCT=$product \
TARGET_BUILD_VARIANT=$variant \
TARGET_PLATFORM_VERSION=$version \
#build_build_var_cache()最终会执行到soong_ui.bash
build_build_var_cache
if [ $? -ne 0 ]
then
if [[ "$product" =~ .*_(eng|user|userdebug) ]]
then
echo "Did you mean -${product/*_/}? (dash instead of underscore)"
fi
return 1
fi
#get_build_var()最终会执行到soong_ui.bash
export TARGET_PRODUCT=$(get_build_var TARGET_PRODUCT)
export TARGET_BUILD_VARIANT=$(get_build_var TARGET_BUILD_VARIANT)
if [ -n "$version" ]; then
export TARGET_PLATFORM_VERSION=$(get_build_var TARGET_PLATFORM_VERSION)
else
unset TARGET_PLATFORM_VERSION
fi
#省略部分代码
}
# Get the exact value of a build variable.
function get_build_var()
{
if [ "$BUILD_VAR_CACHE_READY" = "true" ]
then
eval "echo \"\${var_cache_$1}\""
return 0
fi
local T=$(gettop)
if [ ! "$T" ]; then
echo "Couldn't locate the top of the tree. Try setting TOP." >&2
return 1
fi
#执行soong_ui.bash
(\cd $T; build/soong/soong_ui.bash --dumpvar-mode $1)
}lunch()函数最终会执行build/soong/soong_ui.bash脚本
bash
#记录了开始构建时的精确时间戳，以毫秒为单位
export TRACE_BEGIN_SOONG=$(date +%s%N)
# Function to find top of the source tree (if $TOP isn't set) by walking up the
# tree.
#定义gettop函数
function gettop
{
#找到源代码树的根目录,如果环境变量 TOP 已经设置并且对应的路径存在 build/soong/root.bp 文件，那么函数将返回该路径；否则，它将从当前目录向上查找，直到找到名为 build/soong/root.bp 的文件。
local TOPFILE=build/soong/root.bp
if [ -n "${TOP-}" -a -f "${TOP-}/${TOPFILE}" ] ; then
# The following circumlocution ensures we remove symlinks from TOP.
(cd $TOP; PWD= /bin/pwd)
else
if [ -f $TOPFILE ] ; then
# The following circumlocution (repeated below as well) ensures
# that we record the true directory name and not one that is
# faked up with symlink names.
PWD= /bin/pwd
else
local HERE=$PWD
T=
while [ \( ! \( -f $TOPFILE \) \) -a \( $PWD != "/" \) ]; do
\cd ..
T=`PWD= /bin/pwd -P`
done
\cd $HERE
if [ -f "$T/$TOPFILE" ]; then
echo $T
fi
fi
fi
}
#将当前工作目录（PWD）保存到环境变量 ORIGINAL_PWD 中
# Save the current PWD for use in soong_ui
export ORIGINAL_PWD=${PWD}
#调用 gettop 函数，并将返回的结果保存到环境变量 TOP 中
export TOP=$(gettop)
#加载 microfactory.bash 脚本，该脚本应该位于 TOP 环境变量所指示的路径中
source ${TOP}/build/soong/scripts/microfactory.bash
#调用 Android 构建系统的soong_ui，具体构建和运行某些组件
soong_build_go soong_ui android/soong/cmd/soong_ui
soong_build_go mk2rbc android/soong/mk2rbc/cmd
soong_build_go rbcrun rbcrun/cmd
#将当前目录切换到 TOP 环境变量所指示的路径
cd ${TOP}
#执行 soong_ui 程序，其路径为 getoutdir 环境变量的值，参数为 $@（表示所有传入的命令行参数）
exec "$(getoutdir)/soong_ui" "$@"上面在执行soong_build_go soong_ui android/soong/cmd/soong_ui时，会执行/build/soong/cmd/soong_ui/main.go中的main()函数
go
func main() {
//省略部分代码，省略的代码为构造build.Findsources()函数所需要的参数
// Create a source finder.
f := build.NewSourceFinder(buildCtx, config)
defer f.Shutdown()
//寻找资源文件
build.FindSources(buildCtx, config, f)
c.run(buildCtx, config, args, logsDir)
}在/build/soong/cmd/soong_ui/main.go中的main()函数中，核心主要是通过build.FindSources()去寻找所有的makefile文件和bp文件
go
// FindSources searches for source files known to <f> and writes them to the filesystem for
// use later.
func FindSources(ctx Context, config Config, f *finder.Finder) {
// note that dumpDir in FindSources may be different than dumpDir in NewSourceFinder
// if a caller such as multiproduct_kati wants to share one Finder among several builds
dumpDir := config.FileListDir()
os.MkdirAll(dumpDir, 0777)
// Stop searching a subdirectory recursively after finding an Android.mk.
//寻找所有的Android.mk文件，并添加到Android.mk.list中
androidMks := f.FindFirstNamedAt(".", "Android.mk")
err := dumpListToFile(ctx, config, androidMks, filepath.Join(dumpDir, "Android.mk.list"))
if err != nil {
ctx.Fatalf("Could not export module list: %v", err)
}
// Gate collecting/reporting mk metrics on builds that specifically request
// it, as identifying the total number of mk files adds 4-5ms onto null
// builds.
if config.reportMkMetrics {
androidMksTotal := f.FindNamedAt(".", "Android.mk")
ctx.Metrics.SetToplevelMakefiles(len(androidMks))
ctx.Metrics.SetTotalMakefiles(len(androidMksTotal))
ctx.Metrics.DumpMkMetrics(config.MkMetrics())
}
// Stop searching a subdirectory recursively after finding a CleanSpec.mk.
//寻找所有的CleanSpec.mk文件，并添加到CleanSpec.mk.list中
cleanSpecs := f.FindFirstNamedAt(".", "CleanSpec.mk")
err = dumpListToFile(ctx, config, cleanSpecs, filepath.Join(dumpDir, "CleanSpec.mk.list"))
if err != nil {
ctx.Fatalf("Could not export module list: %v", err)
}
// Only consider AndroidProducts.mk in device/, vendor/ and product/, recursively in these directories.
//寻找所有的AndroidProducts.mk文件，并添加到AndroidProducts.mk.list中
androidProductsMks := f.FindNamedAt("device", "AndroidProducts.mk")
androidProductsMks = append(androidProductsMks, f.FindNamedAt("vendor", "AndroidProducts.mk")...)
androidProductsMks = append(androidProductsMks, f.FindNamedAt("product", "AndroidProducts.mk")...)
err = dumpListToFile(ctx, config, androidProductsMks, filepath.Join(dumpDir, "AndroidProducts.mk.list"))
if err != nil {
ctx.Fatalf("Could not export product list: %v", err)
}
// Recursively look for all Bazel related files.
bazelFiles := f.FindMatching(".", findBazelFiles)
err = dumpListToFile(ctx, config, bazelFiles, filepath.Join(dumpDir, "bazel.list"))
if err != nil {
ctx.Fatalf("Could not export bazel BUILD list: %v", err)
}
// Recursively look for all OWNERS files.
owners := f.FindNamedAt(".", "OWNERS")
err = dumpListToFile(ctx, config, owners, filepath.Join(dumpDir, "OWNERS.list"))
if err != nil {
ctx.Fatalf("Could not find OWNERS: %v", err)
}
// Recursively look for all TEST_MAPPING files.
testMappings := f.FindNamedAt(".", "TEST_MAPPING")
err = dumpListToFile(ctx, config, testMappings, filepath.Join(dumpDir, "TEST_MAPPING.list"))
if err != nil {
ctx.Fatalf("Could not find TEST_MAPPING: %v", err)
}
// Recursively look for all Android.bp files
//寻找所有的Android.bp文件，并添加到Android.bp.list中
androidBps := f.FindNamedAt(".", "Android.bp")
if len(androidBps) == 0 {
ctx.Fatalf("No Android.bp found")
}
err = dumpListToFile(ctx, config, androidBps, filepath.Join(dumpDir, "Android.bp.list"))
if err != nil {
ctx.Fatalf("Could not find modules: %v", err)
}
// Recursively look for all product/board config files.
configurationFiles := f.FindMatching(".", findProductAndBoardConfigFiles)
err = dumpListToFile(ctx, config, configurationFiles, filepath.Join(dumpDir, "configuration.list"))
if err != nil {
ctx.Fatalf("Could not export product/board configuration list: %v", err)
}
if config.Dist() {
f.WaitForDbDump()
// Dist the files.db plain text database.
distFile(ctx, config, f.DbPath, "module_paths")
}
}执行完build.FindSources()后，所有的AndroidProduct.mk文件都将被发现，这时就能展示所有的lunch combo项，然后根据用户选择的combo，选择对应的AndroidProduct.mk。
最后执行make -j16命令后，调用build/envsetup.sh里面的make()函数，最终会根据对应AndroidProduct.mk的规则，选择对应的product.mk进行编译。
移植思路
了解了product编译流程后，自然而然我们能想到的移植思路是，在72. sdk_pc_x86_64-userdebug的AndroidProduct.mk文件里配置71. sdk_car_x86_64-userdebug的product.mk，也就是将72. sdk_pc_x86_64-userdebug的编译流程改向71. sdk_car_x86_64-userdebug的编译流程，这样我们的目标product就会按照车载product的配置进行编译了。查看车载product的编译配置，即打开sdk_car_x86_64.mk文件
makefile
PRODUCT_PACKAGE_OVERLAYS := device/generic/car/common/overlay
$(call inherit-product, device/generic/car/emulator/aosp_car_emulator.mk)
$(call inherit-product, $(SRC_TARGET_DIR)/product/sdk_x86_64.mk)
EMULATOR_VENDOR_NO_SOUND := true
PRODUCT_NAME := sdk_car_x86_64
PRODUCT_DEVICE := emulator_car_x86_64
PRODUCT_BRAND := Android
PRODUCT_MODEL := Car on x86_64 emulator可以看到，这里只是继承了device/generic/car/emulator/aosp_car_emulator.mk和$(SRC_TARGET_DIR)/product/sdk_x86_64.mk这两个makefile文件，以及添加了PRODUCT_PACKAGE_OVERLAYS和EMULATOR_VENDOR_NO_SOUND两项配置，我们将这些配置全部复制到sdk_pc_x86_64.mk中
当然，PRODUCT_NAME是不能变的，并且PRODUCT_DEVICE选择车载的硬件配置。
最后执行编译
shell
source build/envsetup.sh
lunch sdk_pc_x86_64-userdebug
make -j16等待编译完成，启动模拟器
shell
emulator完美进入automotive，并且Model显示我们自定义的名称
