Android system property赋值和sepolicy定义

参考：
https://source.android.google.cn/docs/core/architecture/configuration/add-system-properties#property-name

场景：在定义一个property，并在SystemServer进程中读取

1, system property赋值：

device/***/system_property.mk

# vendor property:
#PRODUCT_PROPERTY_OVERRIDES += \
#       ro.mygroup.test=1

# system property
PRODUCT_SYSTEM_DEFAULT_PROPERTIES += \
       ro.mygroup.test=1

system_property.mk被device mk引用
device/***/BoardConfig.mk

$(call inherit-product, device/***/system_property.mk)

2, 定义sepolicy主体，以及getprop权限

device///sepolicy/property_contexts

ro.mygroup.test    u:object_r:my_property_test:s0 exact string

device///sepolicy/my_property_demo.te

system_public_prop(my_property_test)

get_prop(system_server, my_property_test)

将sepolocy加入编译
device/***/BoardConfig.mk

# BOARD_SEPOLICY_DIRS += device/**/sepolicy/
SYSTEM_EXT_PUBLIC_POLICY += device/**/sepolicy/

3, system_server访问property

String value = SystemProperties.get("ro.mygroup.test", "");