?配套系列教学视频链接：
? ? ??安卓系列教程之ROM系统开发-百问100ask
说明
系统：Android10.0
设备： FireFly RK3399 （ROC-RK3399-PC-PLUS）
前言
init进程在启动会去加载后缀为.prop的属性问文件， 将属性文件中的属性加载到共享内存中， 这样系统就有了默认的一些属性， 本章节介绍常见属性文件，以及这些文件是如何生成的。
一，属性文件介绍
init进程启动代码system/core/init/property_service.cpp，会调用如下函数来加载属性：
void property_load_boot_defaults(bool load_debug_prop) {
// TODO(b/117892318): merge prop.default and build.prop files into one
// We read the properties and their values into a map, in order to always allow properties
// loaded in the later property files to override the properties in loaded in the earlier
// property files, regardless of if they are "ro." properties or not.
std::map<std::string, std::string> properties;
if (!load_properties_from_file("/system/etc/prop.default", nullptr, &properties)) {
// Try recovery path
if (!load_properties_from_file("/prop.default", nullptr, &properties)) {
// Try legacy path
load_properties_from_file("/default.prop", nullptr, &properties);
}
}
load_properties_from_file("/system/build.prop", nullptr, &properties);
load_properties_from_file("/vendor/default.prop", nullptr, &properties);
load_properties_from_file("/vendor/build.prop", nullptr, &properties);
if (SelinuxGetVendorAndroidVersion() >= __ANDROID_API_Q__) {
load_properties_from_file("/odm/etc/build.prop", nullptr, &properties);
} else {
load_properties_from_file("/odm/default.prop", nullptr, &properties);
load_properties_from_file("/odm/build.prop", nullptr, &properties);
}
load_properties_from_file("/product/build.prop", nullptr, &properties);
load_properties_from_file("/product_services/build.prop", nullptr, &properties);
load_properties_from_file("/factory/factory.prop", "ro.*", &properties);
if (load_debug_prop) {
LOG(INFO) << "Loading " << kDebugRamdiskProp;
load_properties_from_file(kDebugRamdiskProp, nullptr, &properties);
}
for (const auto& [name, value] : properties) {
std::string error;
if (PropertySet(name, value, &error) != PROP_SUCCESS) {
LOG(ERROR) << "Could not set '" << name << "' to '" << value
<< "' while loading .prop files" << error;
}
}
property_initialize_ro_product_props();
property_derive_build_fingerprint();
update_sys_usb_config();
}
以上会显示加载属性文件的先后顺序， 文件里面的内容大概如下格式：
ro.actionable_compatible_property.enabled=true
ro.postinstall.fstab.prefix=/system
ro.secure=1
security.perf_harden=1
常见的属性文件介绍如下：
| /system/etc/prop.default | 设置ro.debuggable，?vm，dex优化相关属性，如果没有该文件，就尝试加载/prop.default，再没有就加载/default.prop |
| /system/build.prop | 系统编译属性，如ro.system.build.date系统编译时间，版本等， |
| /vendor/default.prop | 厂商默认属性，?如： ro.bionic.arch=arm64 ro.bionic.cpu_variant=cortex-a53 ro.bionic.2nd_arch=arm ro.bionic.2nd_cpu_variant=cortex-a15 |
| /vendor/build.prop | 厂商编译属性，?如厂商型号，cpu abi列表： ro.vendor.product.cpu.abilist32=armeabi-v7a,armeabi ro.vendor.product.cpu.abilist64=arm64-v8a ro.product.board=rk30sdk ro.board.platform=rk3399 |
| /odm/etc/build.prop | odm编译属性，记录编译时间， 产品信息, 支持的cpu结构: ro.odm.product.cpu.abilist=arm64-v8a,armeabi-v7a,armeabi ro.odm.product.cpu.abilist32=armeabi-v7a,armeabi ro.odm.product.cpu.abilist64=arm64-v8a ro.odm.build.id=QD4A.200805.003 ro.odm.build.tags=release-keys ro.odm.build.type=userdebug ro.product.odm.brand=rockchip ro.product.odm.device=rk3399_roc_pc_plus ro.product.odm.manufacturer=rockchip ro.product.odm.model=ROC-RK3399-PC-PLUS ro.product.odm.name=rk3399_roc_pc_plus Android Q以下版本是找/odm/default.prop和/odm/build.prop |
| /product/build.prop | 产品编译属性：也是记录编译时间， 产品信息: ro.product.product.brand=rockchip ro.product.product.device=rk3399_roc_pc_plus ro.product.product.manufacturer=rockchip ro.product.product.model=ROC-RK3399-PC-PLUS ro.product.product.name=rk3399_roc_pc_plus |
?二， 属性文件内容的组成
属性文件中的属性是来自哪里的呢？比如/system/build.prop，其实可以直接查看里面的内容，是由以下信息组成的：
| build/make/tools/buildinfo_common.sh build/make/tools/buildinfo.sh | 两个脚本会根据build/core/version_defaults.mk里获取各种变量值来赋值给不同属性 |
| device/rockchip/rk3399/rk3399_roc_pc_plus/system.prop | 实际是一个变量system_prop_file包含的值 |
| ADDITIONAL_BUILD_PROPERTIES | 主要是PRODUCT_PROPERTY_OVERRIDES这个变量赋值， 而这个变量就是我们开发时经常用于自定义属性的， 一般在产品配置目录下定义， 另外就是main.mk中默认增加的属性 |
?
?在./build/make/core/main.mk中可以清晰的看到ADDITIONAL_BUILD_PROPERTIES里面包含了什么：
179 ifneq ($(BOARD_PROPERTY_OVERRIDES_SPLIT_ENABLED), true)
?180 ??ADDITIONAL_BUILD_PROPERTIES += $(PRODUCT_PROPERTY_OVERRIDES)
?181 else
?182 ??ifndef BOARD_VENDORIMAGE_FILE_SYSTEM_TYPE
?183 ????ADDITIONAL_BUILD_PROPERTIES += $(PRODUCT_PROPERTY_OVERRIDES)
?184 ??endif
?185 endif
231 ifneq ($(TARGET_BUILD_VARIANT),user)
?232 ??ADDITIONAL_BUILD_PROPERTIES?+= ro.bionic.ld.warning=1
?233 else
?234 # Enable it for user builds as long as they are not final.
?235 ifneq ($(PLATFORM_VERSION_CODENAME),REL)
?236 ??ADDITIONAL_BUILD_PROPERTIES?+= ro.bionic.ld.warning=1
?237 endif
?238 endif
?239
240?ADDITIONAL_BUILD_PROPERTIES?+= ro.treble.enabled=${PRODUCT_FULL_TREBLE}
?其实PRODUCT_PROPERTY_OVERRIDES就比较重要， 我们定制新的默认属性，经常在mk文件中给这个变量赋值。
?/vendor/build.prop内容是由以下信息组成的:
特定的几个产品和厂商相关属性
build/make/tools/buildinfo_common.sh
BOOTIMAGE_BUILD_PROPERTIES
ADDITIONAL VENDOR BUILD PROPERTIES
三， 属性文件的生成过程
至于这些文件具体是如何生成的，可以直接在build/make/core/Makefile文件中搜索:
build.prop, vendor build.prop, odm build.prop, product build.prop, vendor default.prop等关键词，就可以知道如下：
195 # -----------------------------------------------------------------198 BUILDINFO_SH?:= build/make/tools/buildinfo.sh
199 BUILDINFO_COMMON_SH?:= build/make/tools/buildinfo_common.sh
build/make/tools/buildinfo.sh脚本：
#!/bin/bash
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.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.release=$PLATFORM_VERSION"
echo "ro.build.version.security_patch=$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=$BOARD_BUILD_SYSTEM_ROOT_IMAGE"
fi
if [ -n "$AB_OTA_UPDATER" ] ; then
echo "ro.build.ab_update=$AB_OTA_UPDATER"
fi
# These values are deprecated, use "ro.product.cpu.abilist"
# instead (see below).
echo "# ro.product.cpu.abi and ro.product.cpu.abi2 are obsolete,"
echo "# use ro.product.cpu.abilist instead."
echo "ro.product.cpu.abi=$TARGET_CPU_ABI"
if [ -n "$TARGET_CPU_ABI2" ] ; then
echo "ro.product.cpu.abi2=$TARGET_CPU_ABI2"
fi
echo "ro.product.cpu.abilist=$TARGET_CPU_ABI_LIST"
echo "ro.product.cpu.abilist32=$TARGET_CPU_ABI_LIST_32_BIT"
echo "ro.product.cpu.abilist64=$TARGET_CPU_ABI_LIST_64_BIT"
if [ -n "$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"?build/make/tools/buildinfo_common.sh脚本
#!/bin/bash
partition="$1"
if [ "$#" -ne 1 ]; then
echo "Usage: $0 <partition>" 1>&2
exit 1
fi
echo "# begin common build properties"
echo "# autogenerated by $0"
echo "ro.${partition}.build.date=`$DATE`"
echo "ro.${partition}.build.date.utc=`$DATE +%s`"
echo "ro.${partition}.build.fingerprint=$BUILD_FINGERPRINT"
echo "ro.${partition}.build.id=$BUILD_ID"
echo "ro.${partition}.build.tags=$BUILD_VERSION_TAGS"
echo "ro.${partition}.build.type=$TARGET_BUILD_TYPE"
echo "ro.${partition}.build.version.incremental=$BUILD_NUMBER"
echo "ro.${partition}.build.version.release=$PLATFORM_VERSION"
echo "ro.${partition}.build.version.sdk=$PLATFORM_SDK_VERSION"
echo "ro.product.${partition}.brand=$PRODUCT_BRAND"
echo "ro.product.${partition}.device=$PRODUCT_DEVICE"
echo "ro.product.${partition}.manufacturer=$PRODUCT_MANUFACTURER"
echo "ro.product.${partition}.model=$PRODUCT_MODEL"
echo "ro.product.${partition}.name=$PRODUCT_NAME"
echo "# end common build properties"system/build.prop文件的生成过程， 在build/make/core/Makefile中有如下描述
391 ifdef TARGET_SYSTEM_PROP
392 system_prop_file := $(TARGET_SYSTEM_PROP)
393 else
394 system_prop_file := $(wildcard $(TARGET_DEVICE_DIR)/system.prop)
395 endif
396 $(intermediate_system_build_prop): $(BUILDINFO_SH) $(BUILDINFO_COMMON_SH) $(INTERNAL_BUILD_ID_MAKEFILE) $(BUILD_SYSTEM)/version_defaults.mk $(system_prop_file) $(INSTALLED_ANDROID_INFO_TXT_TARGET) $(API_FINGERPRINT)
397 @echo Target buildinfo: $@
398 @mkdir -p $(dir $@)
399 $(hide) echo > $@
400 ifneq ($(PRODUCT_OEM_PROPERTIES),)
401 $(hide) echo "#" >> $@; \
402 echo "# PRODUCT_OEM_PROPERTIES" >> $@; \
403 echo "#" >> $@;
404 $(hide) $(foreach prop,$(PRODUCT_OEM_PROPERTIES), \
405 echo "import /oem/oem.prop $(prop)" >> $@;)
406 endif
407 $(hide) PRODUCT_BRAND="$(PRODUCT_SYSTEM_BRAND)" \
408 PRODUCT_MANUFACTURER="$(PRODUCT_SYSTEM_MANUFACTURER)" \
409 PRODUCT_MODEL="$(PRODUCT_SYSTEM_MODEL)" \
410 PRODUCT_NAME="$(PRODUCT_SYSTEM_NAME)" \
411 PRODUCT_DEVICE="$(PRODUCT_SYSTEM_DEVICE)" \
412 $(call generate-common-build-props-with-product-vars-set,system,$@)
413 $(hide) TARGET_BUILD_TYPE="$(TARGET_BUILD_VARIANT)" \
414 TARGET_BUILD_FLAVOR="$(TARGET_BUILD_FLAVOR)" \
415 TARGET_DEVICE="$(TARGET_DEVICE)" \
416 PRODUCT_DEFAULT_LOCALE="$(call get-default-product-locale,$(PRODUCT_LOCALES))" \
417 PRODUCT_DEFAULT_WIFI_CHANNELS="$(PRODUCT_DEFAULT_WIFI_CHANNELS)" \
418 PRIVATE_BUILD_DESC="$(PRIVATE_BUILD_DESC)" \
419 BUILD_ID="$(BUILD_ID)" \
420 BUILD_DISPLAY_ID="$(BUILD_DISPLAY_ID)" \
421 DATE="$(DATE_FROM_FILE)" \
422 BUILD_USERNAME="$(BUILD_USERNAME)" \
423 BUILD_HOSTNAME="$(BUILD_HOSTNAME)" \
424 BUILD_NUMBER="$(BUILD_NUMBER_FROM_FILE)" \
425 BOARD_BUILD_SYSTEM_ROOT_IMAGE="$(BOARD_BUILD_SYSTEM_ROOT_IMAGE)" \
426 AB_OTA_UPDATER="$(AB_OTA_UPDATER)" \
427 PLATFORM_VERSION="$(PLATFORM_VERSION)" \
428 PLATFORM_SECURITY_PATCH="$(PLATFORM_SECURITY_PATCH)" \
429 PLATFORM_BASE_OS="$(PLATFORM_BASE_OS)" \
430 PLATFORM_SDK_VERSION="$(PLATFORM_SDK_VERSION)" \
431 PLATFORM_PREVIEW_SDK_VERSION="$(PLATFORM_PREVIEW_SDK_VERSION)" \
432 PLATFORM_PREVIEW_SDK_FINGERPRINT="$$(cat $(API_FINGERPRINT))" \
433 PLATFORM_VERSION_CODENAME="$(PLATFORM_VERSION_CODENAME)" \
434 PLATFORM_VERSION_ALL_CODENAMES="$(PLATFORM_VERSION_ALL_CODENAMES)" \
435 PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION="$(PLATFORM_MIN_SUPPORTED_TARGE_SDK_VERSION)" \
436 BUILD_VERSION_TAGS="$(BUILD_VERSION_TAGS)" \
437 $(if $(OEM_THUMBPRINT_PROPERTIES),BUILD_THUMBPRINT="$(BUILD_THUMBPRINT_FROM_FILE)") \
438 TARGET_CPU_ABI_LIST="$(TARGET_CPU_ABI_LIST)" \
439 TARGET_CPU_ABI_LIST_32_BIT="$(TARGET_CPU_ABI_LIST_32_BIT)" \
440 TARGET_CPU_ABI_LIST_64_BIT="$(TARGET_CPU_ABI_LIST_64_BIT)" \
441 TARGET_CPU_ABI="$(TARGET_CPU_ABI)" \
442 TARGET_CPU_ABI2="$(TARGET_CPU_ABI2)" \
443 bash $(BUILDINFO_SH) >> $@
444 $(hide) $(foreach file,$(system_prop_file), \
445 if [ -f "$(file)" ]; then \
446 echo Target buildinfo from: "$(file)"; \
447 echo "" >> $@; \
448 echo "#" >> $@; \
449 echo "# from $(file)" >> $@; \
450 echo "#" >> $@; \
451 cat $(file) >> $@; \
452 echo "# end of $(file)" >> $@; \
453 fi;)
454 $(if $(FINAL_BUILD_PROPERTIES), \
455 $(hide) echo >> $@; \
456 echo "#" >> $@; \
457 echo "# ADDITIONAL_BUILD_PROPERTIES" >> $@; \
458 echo "#" >> $@; )
459 $(hide) $(foreach line,$(FINAL_BUILD_PROPERTIES), \
460 echo "$(line)" >> $@;)
461 $(hide) build/make/tools/post_process_props.py $@ $(PRODUCT_SYSTEM_PROPERTY_BLACKLIST)
462
463 build_desc :=
464
465 ifeq (,$(filter true, $(TARGET_NO_KERNEL) $(TARGET_NO_RECOVERY)))
466 INSTALLED_RECOVERYIMAGE_TARGET := $(PRODUCT_OUT)/recovery.img
467 else
468 INSTALLED_RECOVERYIMAGE_TARGET :=
469 endif
470
471 $(INSTALLED_BUILD_PROP_TARGET): $(intermediate_system_build_prop) $(INSTALLED_RECOVERYIMAGE_TARGET)
472 @echo "Target build info: $@"
473 $(hide) grep -v 'ro.product.first_api_level' $(intermediate_system_build_prop) > $@
474 ?上面大体是如下过程：
1，buildinfo.sh和buildinfo_common.sh脚本会输出很多property值给build.prop
2，system_prop_file变量代表的文件的内容会被到build.prop文件里去，system_prop_file代表的文件可以由TARGET_SYSTEM_PROP变量定义,也可以是device目录下的system.prop文件， 在build目录搜索结果如下：
./build/make/core/Makefile:404:system_prop_file := $(TARGET_SYSTEM_PROP)
./build/make/core/Makefile:406:system_prop_file := $(wildcard $(TARGET_DEVICE_DIR)/system.prop)
3，ADDITIONAL_BUILD_PROPERTIES主要是PRODUCT_PROPERTY_OVERRIDES这个变量赋值， 而这个变量就是我们开发时经常用于自定义属性的， 一般在产品配置目录下定义， 另外就是main.mk中默认增加的属性
4，将out/target/product/${target_device}/obj/ETC/system_build_prop_intermediates里的build.prop拷贝到out/target/product/${target_device}/system/目录下
?大家在看build/make/core/Makefile时可能涉及到一下函数，?很多函数都是在build/core/definitions.mk中定义:
| collapse-pairs | 作用是将ADDITIONAL_DEFAULT_PROPERTIES和PRODUCT_DEFAULT_PROPERTY_OVERRIDES两个变量里的所有赋值语句’=’两端的空格去掉 |
| uniq-pairs-by-first-component | 作用就是对ADDITIONAL_DEFAULT_PROPERTIES里的赋值语句去重，如果有发现对同一个property_name赋值多次，则只保留第一个值。 |
| post_process_props.py | 用法： post_process_props.py $@ (PRODUCT_SYSTEM_PROPERTY_BLACKLIST) 作用：? 删除default.prop文件中指定的property(在函数的第二个参数中指定，没有则表明不指定)，并且检查每个property名字和值的长度是否超过最大值，在这个python脚本中还可以根据需求再修改一次property值作为预置。 |
?/vendor/build.prop文件生成的过程：
?
482 ifdef?property_overrides_split_enabled
483 FINAL_VENDOR_BUILD_PROPERTIES?+= \
484 ????$(call?collapse-pairs, $(PRODUCT_PROPERTY_OVERRIDES))
485 FINAL_VENDOR_BUILD_PROPERTIES?:= $(call?uniq-pairs-by-first-component, \
486 ????$(FINAL_VENDOR_BUILD_PROPERTIES),=)
487 endif??# property_overrides_split_enabled
488
489 $(INSTALLED_VENDOR_BUILD_PROP_TARGET): $(BUILDINFO_COMMON_SH) $(intermediate_system_build_prop)
490 @echo?Target?vendor?buildinfo: $@
491 @mkdir?-p $(dir?$@)
492 $(hide) echo?> $@
493 ifeq?($(PRODUCT_USE_DYNAMIC_PARTITIONS),true)
494 $(hide) echo?ro.boot.dynamic_partitions=true?>> $@
495 endif
496 ifeq?($(PRODUCT_RETROFIT_DYNAMIC_PARTITIONS),true)
497 $(hide) echo?ro.boot.dynamic_partitions_retrofit=true?>> $@
498 endif
499 $(hide) grep?'ro.product.first_api_level'?$(intermediate_system_build_prop) >> $@ || true
500 $(hide) echo?ro.vendor.build.security_patch="$(VENDOR_SECURITY_PATCH)">>$@
501 $(hide) echo?ro.vendor.product.cpu.abilist="$(TARGET_CPU_ABI_LIST)">>$@
502 $(hide) echo?ro.vendor.product.cpu.abilist32="$(TARGET_CPU_ABI_LIST_32_BIT)">>$@
503 $(hide) echo?ro.vendor.product.cpu.abilist64="$(TARGET_CPU_ABI_LIST_64_BIT)">>$@
504 $(hide) echo?ro.product.board="$(TARGET_BOOTLOADER_BOARD_NAME)">>$@
505 $(hide) echo?ro.board.platform="$(TARGET_BOARD_PLATFORM)">>$@
506 $(hide) echo?ro.hwui.use_vulkan="$(TARGET_USES_VULKAN)">>$@
507 ifdef?TARGET_SCREEN_DENSITY
508 $(hide) echo?ro.sf.lcd_density="$(TARGET_SCREEN_DENSITY)">>$@
509 endif
510 $(hide) $(call?generate-common-build-props,vendor,$@)
511 $(hide) echo?"#"?>> $@; \
512 ????????echo?"# BOOTIMAGE_BUILD_PROPERTIES"?>> $@; \
513 ????????echo?"#"?>> $@;
514 $(hide) echo?ro.bootimage.build.date=`$(DATE_FROM_FILE)`>>$@
515 $(hide) echo?ro.bootimage.build.date.utc=`$(DATE_FROM_FILE) +%s`>>$@
516 $(hide) echo?ro.bootimage.build.fingerprint="$(BUILD_FINGERPRINT_FROM_FILE)">>$@
517 $(hide) echo?"#"?>> $@; \
518 ????????echo?"# ADDITIONAL VENDOR BUILD PROPERTIES"?>> $@; \
519 ????????echo?"#"?>> $@;
520 $(hide) cat?$(INSTALLED_ANDROID_INFO_TXT_TARGET) | grep?'require version-'?| sed?-e 's/require?version-/ro.build.expect./g'?>> $@
521 ifdef?property_overrides_split_enabled
522 $(hide) $(foreach?line,$(FINAL_VENDOR_BUILD_PROPERTIES), \
523 ????echo?"$(line)"?>> $@;)
524 endif??# property_overrides_split_enabled
525 $(hide) build/make/tools/post_process_props.py?$@ $(PRODUCT_VENDOR_PROPERTY_BLACKLIST)
??四， 总结
了解属性文件的生成过程， 就可以很方便的去定制系统默认的属性， 比如修改system.prop文件， 新增变量PRODUCT_PROPERTY_OVERRIDES。