Android 的系统属性包括两部分:文件保存的持久属性和每次开机导入的cache属性。前者主要保存在下面几个文件中:
bionic / libc / include / sys / _system_properties.h
- #define PROP_SERVICE_NAME "property_service"
- #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"
后者则通过frameworks/base/core/java/android/os/SystemProperties.java的接口定义,
- private static native String native_get(String key);
- private static native String native_get(String key, String def);
- private static native void native_set(String key, String def);
- public static void set(String key, String val) {
- if (key.length() > PROP_NAME_MAX) {
- throw new IllegalArgumentException( " key.length > " + PROP_NAME_MAX);
- }
- if (val != null && val.length() > PROP_VALUE_MAX) {
- throw new IllegalArgumentException( " val.length > " +
- PROP_VALUE_MAX);
- }
- native_set(key, val);
- }
该接口类在初始化运行环境中注册对应的cpp接口android_os_SystemProperties.cpp,实际操作通过JNI调用的是cpp文件对应的接口:
frameworks/base/core/jni/AndroidRuntime.cpp
- namespace android {
- extern int register_android_os_SystemProperties(JNIEnv * env);
- }
frameworks/base/core/jni/android_os_SystemProperties.cpp
- static void SystemProperties_set(JNIEnv * env, jobject clazz, jstring keyJ, jstring valJ)
- {
- int err;
- const char * key;
- const char * val;
- key = env -> GetStringUTFChars(keyJ, NULL);
- if (valJ == NULL) {
- val = "" ; /* NULL pointer not allowed here */
- } else {
- val = env -> GetStringUTFChars(valJ, NULL);
- }
- err = property_set(key, val);
- env -> ReleaseStringUTFChars(keyJ, key);
- if (valJ != NULL) {
- env -> ReleaseStringUTFChars(valJ, val);
- }
- }
设置key的value时,需要作鉴权,根据设置程序所在进程的fd获知uid值,比如system server进程可以设置net打头的key,不可以设置gsm打头的key,相关的定义如下:
system/core/include/private/android_filesystem_config.h
- #define AID_ROOT 0 /* traditional unix root user */
- #define AID_SYSTEM 1000 /* system server */
- #define AID_RADIO 1001 /* telephony subsystem, RIL */
- #define AID_DHCP 1014 /* dhcp client */
- #define AID_SHELL 2000 /* adb and debug shell user */
- #define AID_CACHE 2001 /* cache access */
- #define AID_APP 10000 /* first app user */
system/core/init/property_service.c
- #define PERSISTENT_PROPERTY_DIR "/data/property"
- struct {
- const char * prefix;
- unsigned int uid;
- } property_perms[] = {
- { " net.rmnet0. " , AID_RADIO },
- { " net.gprs. " , AID_RADIO },
- { " ril. " , AID_RADIO },
- { " gsm. " , AID_RADIO },
- { " net.dns " , AID_RADIO },
- { " net.usb0 " , AID_RADIO },
- { " net. " , AID_SYSTEM },
- { " dev. " , AID_SYSTEM },
- { " runtime. " , AID_SYSTEM },
- { " hw. " , AID_SYSTEM },
- { " sys. " , AID_SYSTEM },
- { " service. " , AID_SYSTEM },
- { " wlan. " , AID_SYSTEM },
- { " dhcp. " , AID_SYSTEM },
- { " dhcp. " , AID_DHCP },
- { " debug. " , AID_SHELL },
- { " log. " , AID_SHELL },
- { " service.adb.root " , AID_SHELL },
- { " persist.sys. " , AID_SYSTEM },
- { " persist.service. " , AID_SYSTEM },
- { NULL, 0 }
- };
- int property_set( const char * name, const char * value)
- {
- property_changed(name, value);
- return 0 ;
- }
- int start_property_service( void )
- {
- int fd;
- load_properties_from_file(PROP_PATH_SYSTEM_BUILD);
- load_properties_from_file(PROP_PATH_SYSTEM_DEFAULT);
- load_properties_from_file(PROP_PATH_LOCAL_OVERRIDE);
- /* Read persistent properties after all default values have been loaded. */
- load_persistent_properties();
- fd = create_socket(PROP_SERVICE_NAME, SOCK_STREAM, 0666 , 0 , 0 );
- if (fd < 0 ) return - ;
- fcntl(fd, F_SETFD, FD_CLOEXEC);
- fcntl(fd, F_SETFL, O_NONBLOCK);
- listen(fd, 8 );
- return fd;
- }
- void handle_property_set_fd( int fd)
- {
- switch (msg.cmd) {
- case PROP_MSG_SETPROP:
- msg.name[PROP_NAME_MAX - ] = 0 ;
- msg.value[PROP_VALUE_MAX - ] = 0 ;
- if (memcmp(msg.name, " ctl. " , 4 ) == 0 ) {
- if (check_control_perms(msg.value, cr.uid)) {
- handle_control_message(( char * ) msg.name + 4 , ( char * ) msg.value);
- } else {
- ERROR( " sys_prop: Unable to %s service ctl [%s] uid: %d pid:%d\n " ,
- msg.name + 4 , msg.value, cr.uid, cr.pid);
- }
- } else {
- if (check_perms(msg.name, cr.uid)) {
- property_set(( char * ) msg.name, ( char * ) msg.value);
- } else {
- ERROR( " sys_prop: permission denied uid:%d name:%s\n " ,
- cr.uid, msg.name);
- }
- }
- break ;
- default :
- break ;
- }
- }
在开机启动后的init操作中,会执行一个loop循环,当检测到有新的设置时,进入设置流程,鉴权失败会提示相关的异常,如sys_prop: permission denied uid:000
name:gsm.phone.id
system/core/init/init.c
- void property_changed( const char * name, const char * value)
- {
- if (property_triggers_enabled) {
- queue_property_triggers(name, value);
- drain_action_queue();
- }
- }
- int main( int argc, char ** argv)
- {
- parse_config_file( " /init.rc " );
- qemu_init();
- device_fd = device_init();
- property_init();
- fd = open(console_name, O_RDWR);
- property_set_fd = start_property_service();
- ufds[ 0 ].fd = device_fd;
- ufds[ 0 ].events = POLLIN;
- ufds[ ].fd = property_set_fd;
- ufds[ ].events = POLLIN;
- ufds[ 2 ].fd = signal_recv_fd;
- ufds[ 2 ].events = POLLIN;
- fd_count = 3 ;
- for (;;) {
- if (ufds[ 0 ].revents == POLLIN)
- handle_device_fd(device_fd);
- if (ufds[ ].revents == POLLIN)
- handle_property_set_fd(property_set_fd);
- if (ufds[ 3 ].revents == POLLIN)
- handle_keychord(keychord_fd);
- }
- return 0 ;
- }
来自:http://blog.csdn.net/mars5337/archive/200/07/0/5705840.aspx