Android培训班(38)
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在init.rc文件里，可以看到加载下面的服务：
service dbus /system/bin/dbus-daemon --system --nofork
socket dbus stream 660 bluetooth bluetooth
user bluetooth
group bluetooth net_bt_admin
dbus服务的代码在目录：
Android-2.0/external/dbus/bus
dbus服务是android使用的一种特殊的进程间通讯系统。它具有面向对象接口的协议，以及应用程序之间互相发现和监视的守护进程。dbus设计用来作为用户与系统服务之间的分隔以及系统服务之间的通讯。因此，dbus通讯安全，但效率有点差。
它的主要入口函数代码如下：
int
main (int argc, char **argv)
{
DBusError error;
DBusString config_file;
DBusString addr_fd;
DBusString pid_fd;
const char *prev_arg;
int print_addr_fd;
int print_pid_fd;
int i;
dbus_bool_t print_address;
dbus_bool_t print_pid;
int force_fork;
初始化配置文件／文件句柄／进程ＩＤ。
if (!_dbus_string_init (&config_file))
return 1;
if (!_dbus_string_init (&addr_fd))
return 1;
if (!_dbus_string_init (&pid_fd))
return 1;
print_address = FALSE;
print_pid = FALSE;
force_fork = FORK_FOLLOW_CONFIG_FILE;
下面分析进程输入的参数。
prev_arg = NULL;
i = 1;
while (i < argc)
{
const char *arg = argv[i];
if (strcmp (arg, "--help") == 0 ||
strcmp (arg, "-h") == 0 ||
strcmp (arg, "-?") == 0)
usage ();
else if (strcmp (arg, "--version") == 0)
version ();
else if (strcmp (arg, "--introspect") == 0)
introspect ();
else if (strcmp (arg, "--nofork") == 0)
force_fork = FORK_NEVER;
else if (strcmp (arg, "--fork") == 0)
force_fork = FORK_ALWAYS;
else if (strcmp (arg, "--system") == 0)
{
check_two_config_files (&config_file, "system");
if (!_dbus_string_append (&config_file, DBUS_SYSTEM_CONFIG_FILE))
exit (1);
}
else if (strcmp (arg, "--session") == 0)
{
check_two_config_files (&config_file, "session");
if (!_dbus_string_append (&config_file, DBUS_SESSION_CONFIG_FILE))
exit (1);
}
else if (strstr (arg, "--config-file=") == arg)
{
const char *file;
check_two_config_files (&config_file, "config-file");
file = strchr (arg, '=');
++file;
if (!_dbus_string_append (&config_file, file))
exit (1);
}
else if (prev_arg &&
strcmp (prev_arg, "--config-file") == 0)
{
check_two_config_files (&config_file, "config-file");
if (!_dbus_string_append (&config_file, arg))
exit (1);
}
else if (strcmp (arg, "--config-file") == 0)
; /* wait for next arg */
else if (strstr (arg, "--print-address=") == arg)
{
const char *desc;
check_two_addr_descriptors (&addr_fd, "print-address");
desc = strchr (arg, '=');
++desc;
if (!_dbus_string_append (&addr_fd, desc))
exit (1);
print_address = TRUE;
}
else if (prev_arg &&
strcmp (prev_arg, "--print-address") == 0)
{
check_two_addr_descriptors (&addr_fd, "print-address");
if (!_dbus_string_append (&addr_fd, arg))
exit (1);
print_address = TRUE;
}
else if (strcmp (arg, "--print-address") == 0)
print_address = TRUE; /* and we'll get the next arg if appropriate */
else if (strstr (arg, "--print-pid=") == arg)
{
const char *desc;
check_two_pid_descriptors (&pid_fd, "print-pid");
desc = strchr (arg, '=');
++desc;
if (!_dbus_string_append (&pid_fd, desc))
exit (1);
print_pid = TRUE;
}
else if (prev_arg &&
strcmp (prev_arg, "--print-pid") == 0)
{
check_two_pid_descriptors (&pid_fd, "print-pid");
if (!_dbus_string_append (&pid_fd, arg))
exit (1);
print_pid = TRUE;
}
else if (strcmp (arg, "--print-pid") == 0)
print_pid = TRUE; /* and we'll get the next arg if appropriate */
else
usage ();
prev_arg = arg;
++i;
}
根据输入的参数进行初始化总线。
if (_dbus_string_get_length (&config_file) == 0)
{
fprintf (stderr, "No configuration file specified.\n");
usage ();
}
print_addr_fd = -1;
if (print_address)
{
print_addr_fd = 1; /* stdout */
if (_dbus_string_get_length (&addr_fd) > 0)
{
long val;
int end;
if (!_dbus_string_parse_int (&addr_fd, 0, &val, &end) ||
end != _dbus_string_get_length (&addr_fd) ||
val < 0 || val > _DBUS_INT_MAX)
{
fprintf (stderr, "Invalid file descriptor: \"%s\"\n",
_dbus_string_get_const_data (&addr_fd));
exit (1);
}
print_addr_fd = val;
}
}
_dbus_string_free (&addr_fd);
print_pid_fd = -1;
if (print_pid)
{
print_pid_fd = 1; /* stdout */
if (_dbus_string_get_length (&pid_fd) > 0)
{
long val;
int end;
if (!_dbus_string_parse_int (&pid_fd, 0, &val, &end) ||
end != _dbus_string_get_length (&pid_fd) ||
val < 0 || val > _DBUS_INT_MAX)
{
fprintf (stderr, "Invalid file descriptor: \"%s\"\n",
_dbus_string_get_const_data (&pid_fd));
exit (1);
}
print_pid_fd = val;
}
}
_dbus_string_free (&pid_fd);
if (!bus_selinux_pre_init ())
{
_dbus_warn ("SELinux pre-initialization failed\n");
exit (1);
}
dbus_error_init (&error);
注册监视进程的服务函数。
context = bus_context_new (&config_file, force_fork,
print_addr_fd, print_pid_fd,
&error);
_dbus_string_free (&config_file);
if (context == NULL)
{
_dbus_warn ("Failed to start message bus: %s\n",
error.message);
dbus_error_free (&error);
exit (1);
}
setup_reload_pipe (bus_context_get_loop (context));
_dbus_set_signal_handler (SIGHUP, signal_handler);
_dbus_set_signal_handler (SIGTERM, signal_handler);
#ifdef DBUS_BUS_ENABLE_DNOTIFY_ON_LINUX
_dbus_set_signal_handler (SIGIO, signal_handler);
#endif /* DBUS_BUS_ENABLE_DNOTIFY_ON_LINUX */
_dbus_verbose ("We are on D-Bus...\n");
进入服务循环。
_dbus_loop_run (bus_context_get_loop (context));
bus_context_shutdown (context);
bus_context_unref (context);
bus_selinux_shutdown ();
return 0;
}