1. property应用例子

Java: import android.os.SystemProperties; SystemProperties.get("persist.sys.usb.config", "mtp,adb"); SystemProperties.getBoolean("ro.adb.secure", false); SystemProperties.set("sys.usb.config", config); SystemProperties.set需要有system权限，可以这么做 a. 在Android.mk中，加上LOCAL_CERTIFICATE :=platform b. 在AndroidManifest.xml中，加上android:sharedUserId="android.uid.system"

Native C:

#include <cutils/properties.h> LOCAL_SHARED_LIBRARIES := \  libcutils   int property_set(const char *key, const char *value) int property_get(const char *key, char *value, const char *default_value) property_set("service.adb.root", "1"); property_get("ro.debuggable", value, "")

 

2. 设置属性的调用过程

SystemProperties.set in Java    set frameworks/base/core/java/android/os/SystemProperties.java      native_set(key, val)        SystemProperties_set  frameworks/base/core/jni/android_os_SystemProperties.cpp           property_set    /system/core/libcutils/properties.c

setprop in .rc/.sh file

  setprop_main  system/core/toolbox/setprop.c      property_set  /system/core/libcutils/properties.c

property_set    /system/core/libcutils/properties.c

HAVE_LIBC_SYSTEM_PROPERTIES  #define HAVE_LIBC_SYSTEM_PROPERTIES 1 in build/core/combo/include/arch/linux-arm/AndroidConfig.h   __system_property_set   bionic/libc/bionic/system_properties.c      send_prop_msg(PROP_MSG_SETPROP)        handle_property_set_onfd(case PROP_MSG_SETPROP)  system/core/init/property_service.c          检查权限          if "ctl." 开头  handle_control_message()   system/core/init/init.c               ctrl.start   msg_start()     启动service               ctrl.stop    msg_stop()      停止service               ctrl.restart msg_restart()   重启service          else property_set()              如果能找到且以ro开头，就返回-1；能找到且不以ro开头调用 __system_property_update()              如果找不到则调用__system_property_add()              如果是"net."开头，调用property_set("net.change", name)              如果以"persist."开头，调用write_persistent_property();              property_changed(name, value); 除了"persist."开头的property，关机后值会消失；以"persist."开头的会保存在/data/property目录下一文件里，可以看write_persistent_property()

 

3. 属性的初始值

从下面一些文件可以得到属性的初始值 void start_property_service(void) { ...     load_properties_from_file(PROP_PATH_SYSTEM_BUILD);     load_properties_from_file(PROP_PATH_SYSTEM_DEFAULT);     load_override_properties();     /* Read persistent properties after all default values have been loaded. */     load_persistent_properties(); ... #define PROP_PATH_RAMDISK_DEFAULT   "/default.prop" #define PROP_PATH_SYSTEM_BUILD     "/system/build.prop" #define PROP_PATH_SYSTEM_DEFAULT   "/system/default.prop" #define PROP_PATH_LOCAL_OVERRIDE   "/data/local.prop"

 

4. 属性的权限

如果是serice, 调用check_control_perms()检查权限,可以看看control_perms[] 如果是其他属性，调用check_perms()检查权限，可以看看property_perms[]

 

5. property_changed()  system/core/init/init.c

void property_changed(const char *name, const char *value) {     if (property_triggers_enabled)         queue_property_triggers(name, value); }                queue_property_triggers()    action_add_queue_tail(act)    设置完属性后，会调用on property相应的action,  可以看看init.rc