Android培训班(38)

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } -->

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;

}