Android 的系统属性(SystemProperties)设置分析

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#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"

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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);
}

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namespace  android {
extern   int  register_android_os_SystemProperties(JNIEnv  * env);
}

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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);
}
}

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#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 */

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#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   - 1 ;
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 - 1 ]  =   0 ;
msg.value[PROP_VALUE_MAX - 1 ]  =   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 ;
}
}

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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[ 1 ].fd  =  property_set_fd;
ufds[ 1 ].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[ 1 ].revents  ==  POLLIN)
handle_property_set_fd(property_set_fd);
if  (ufds[ 3 ].revents  ==  POLLIN)
handle_keychord(keychord_fd);
}
return   0 ;
}