DBus Study

最新推荐文章于 2022-07-15 11:04:45 发布

原创最新推荐文章于 2022-07-15 11:04:45 发布 · 860 阅读

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CC 4.0 BY-SA版权

本文通过两个具体的例子介绍了如何使用DBus进行信号发送与接收，并详细记录了解决编译过程中遇到的各种问题，包括头文件缺失及动态链接库配置等。

1, sudo apt-get install dbus-*

2, sudo apt-get install libdbus*

3, example

    #include <stdio.h>
    #include <stdlib.h>
    #include <dbus/dbus.h>
    #include <unistd.h>
     
    const int RES_SUCCESS = -1;
    const int RES_FAILED  = 0;
     
    int my_dbus_initialization(char const * _bus_name, DBusConnection ** _conn) {
        DBusError err;
     
        int ret;
     
        dbus_error_init(&err);
     
        *_conn = dbus_bus_get(DBUS_BUS_SESSION, &err);
        if(dbus_error_is_set(&err)) {
            printf("Connection Error\n");
            dbus_error_free(&err);
            return RES_FAILED;
        }
     
        ret = dbus_bus_request_name(*_conn, _bus_name, DBUS_NAME_FLAG_REPLACE_EXISTING, &err);
        if(dbus_error_is_set(&err)){
            printf("Requece name error \n");
            dbus_error_free(&err);
            return RES_FAILED;
        }
     
        if(DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER != ret) {
            return RES_FAILED;
        }
     
        return RES_SUCCESS;
    }
     
    int my_dbus_send_sigal(DBusConnection * conn) {
        dbus_uint32_t serial = 0;
        DBusMessage* msg;
        DBusMessageIter args;
        char sigvalue[20] = "liyiwen";
     
        msg = dbus_message_new_signal("/test/signal/Object",  // object name
            "test.signal.Type",     // interface name
            "Test");                // name of signal
     
        if (NULL == msg) {
            printf("Message Null");
            return RES_FAILED;
        }
     
        dbus_message_iter_init_append(msg, &args);
     
        printf("%s\n", sigvalue);
        dbus_uint32_t my_age = 10;
        if(!dbus_message_iter_append_basic(&args, DBUS_TYPE_UINT32, &my_age)) {
            printf("Out of memory\n");
            return RES_FAILED;
        }
     
        if(!dbus_connection_send(conn, msg, &serial)) {
            printf("Out of memory");
            return RES_FAILED;
        }
        dbus_connection_flush(conn);
     
        dbus_message_unref(msg);
     
        return RES_SUCCESS;
     
    }
     
    int main(int agrc, char** argv)
    {
        DBusConnection * conn;
     
        printf("Start\n");
        if (RES_FAILED == my_dbus_initialization("test.method.client", &conn)) {
            exit(1);
        }
        my_dbus_send_sigal(conn);
     
        while(1){sleep(10);}
     
        return 0;
    }

#include <stdio.h>
#include <stdlib.h>
#include <dbus/dbus.h>
#include <unistd.h>

const int RES_SUCCESS = -1;
const int RES_FAILED  = 0;

int my_dbus_initialization(char const * _bus_name, DBusConnection **_conn) {
	DBusError err;
	int ret;

	dbus_error_init(&err);

	*_conn = dbus_bus_get(DBUS_BUS_SESSION, &err);
	if(dbus_error_is_set(&err)) {
	    printf("Connection Error(%s) \n", err.message);
	    dbus_error_free(&err);
	    return RES_FAILED;
	}

	ret = dbus_bus_request_name(*_conn, _bus_name, DBUS_NAME_FLAG_REPLACE_EXISTING, &err);
	if(dbus_error_is_set(&err)){
	    printf("Requece name error(%s) \n", err.message);
	    dbus_error_free(&err);
	    return RES_FAILED;
	}
	if(DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER != ret) {
	    return RES_FAILED;
	}
	return RES_SUCCESS;
}

int main(int agrc, char** argv)
{

	DBusError err;
	DBusMessage* msg;
	DBusMessageIter args;

	dbus_error_init(&err);
	DBusConnection *conn;
	if (RES_FAILED == my_dbus_initialization("test.method.server", &conn)) {
	    exit(1);
	}

	dbus_bus_add_match(conn, "type='signal', interface='test.signal.Type'", &err);

	dbus_connection_flush(conn);
	if(dbus_error_is_set(&err)) {
	    printf("dbus_bus_add_match err (%s)", err.message);
	    return RES_FAILED;
	}

	while(1) {
	    dbus_connection_read_write(conn, 0);
	    msg = dbus_connection_pop_message(conn);

	    if(NULL == msg) {
		sleep(1);
		continue;
	    }

	    if(dbus_message_is_signal(msg, "test.signal.Type", "Test")) {
		if(!dbus_message_iter_init(msg, &args)) {
		    printf("dbus_message_iter_init error, msg has no arguments!\n");
		}
		else if (DBUS_TYPE_UINT32 != dbus_message_iter_get_arg_type(&args)){
		    printf("not a uint 32 type !\n");
		}
		else {
		    dbus_uint32_t my_age = 0;
		    dbus_message_iter_get_basic(&args, &my_age);
		    printf("Got signal with value %d\n", my_age);
		}
	    }

	    dbus_message_unref(msg);

	}

	return 0;
}

4, error information fix

编译
----------------------------------------------------------
错误1:
$ gcc test.c
test.c:8:23: 错误： dbus/dbus.h：No such file or directory
......
$
错误提示，dbus库的头文件位置不正确(如果已经安装了dbus的话)
$ sudo updatedb
$ sudo locate dbus.h (查看dbus.h的所在位置)
/usr/local/include/dbus-1.0/dbus/dbus.h
/usr/include/dbus-1.0/dbus/dbus.h
看来dbus.h的存放位置的确不正确，这可能是由于dbus-1.0的安装位置有问题，没关系，调整一下dbus的头文件位置就可以了(调整方法如下):
root@zxl:/usr/include# ln -sf dbus-1.0/dbus

错误2:
$ gcc test.c
在包含自 test.c：8 的文件中:
/usr/include/dbus/dbus.h:29:33: 错误： dbus/dbus-arch-deps.h：No such file or directory
......

依然有头文件无法正确定位的问题，从错误提示来看，该文件应该在/usr/include/dbus/目录下，可是进入该目录查看竟然没有，那就在整个系统中查找该文件。
root@zxl:/usr/include/dbus# locate dbus-arch-deps.h
/usr/local/lib/dbus-1.0/include/dbus/dbus-arch-deps.h
/usr/lib/dbus-1.0/include/dbus/dbus-arch-deps.h
将该文件复制到/usr/include/dbus目录下

错误3:
$ gcc test.c
......
test.c:(.text+0xbb6): undefined reference to `dbus_message_iter_get_basic'
test.c:(.text+0xbd4): undefined reference to `dbus_message_unref'
collect2: ld 返回 1

需要连接动态库dbus
$ cd /usr/lib
$ ls *dbus*
libdbus-1.a libdbus-1.so.3 libdbus-glib-1.so
libdbus-1.la libdbus-1.so.3.2.0 libdbus-glib-1.so.2
libdbus-1.so libdbus-glib-1.a libdbus-glib-1.so.2.1.0

$ gcc test.c -l dbus-1 -o dbus