NetLink機制使用

http://blog.csdn.net/sepnic/article/details/6799476

前些日子研究如何在Android實現USB-Audio的熱插拔，順帶了解了一下netlink機制。netlink在TCP/IP方面用得較多，但根據需要也可用在HDMI/USB等熱插拔消息通知。前人已經對這方面有深入的剖析，這裏就不累述了。一些典型的資料如下：

linux的配置接口-netlink原理和設計

netlink機制-實現系統調用

netlink機制-總結

PF_NETLINK應用實例NETLINK_KOBJECT_UEVENT具體實現－－udev實現原理

linux 內核與用戶空間通信之netlink使用方法

如下是我實現的從內核中獲取USB熱插拔消息的代碼，可根據對消息字符串的解析來定義對應的操作。事實上這種方法並不足夠好（勝在簡便）。比較好的做法是實現點對點，即在內核驅動中用netlink_kernel_create創建一個netlink服務端，發送自定義的消息幀，用戶程序就可接收指定netlink服務端的消息。

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <linux/netlink.h>

#define UEVENT_BUFFER_SIZE 2048

int thread_net_link()
{
    struct sockaddr_nl client;
    struct timeval tv;
    int skfd, rcvlen, ret;
    fd_set fds;
    int buffersize = 1024;

    skfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_KOBJECT_UEVENT);
    memset(&client, 0, sizeof(client));
    client.nl_family = AF_NETLINK;
    client.nl_pid = getpid();
    client.nl_groups = 1; /* receive broadcast message*/
    setsockopt(skfd, SOL_SOCKET, SO_RCVBUF, &buffersize, sizeof(buffersize));
    bind(skfd, (struct sockaddr*)&client, sizeof(client));

    while (1) {
        char buf[UEVENT_BUFFER_SIZE] = { 0 };

        FD_ZERO(&fds);
        FD_SET(skfd, &fds);
        tv.tv_sec = 0;
        tv.tv_usec = 100 * 1000;
        ret = select(skfd + 1, &fds, NULL, NULL, &tv);
        if(ret < 0)
            continue;
        if(!(ret > 0 && FD_ISSET(skfd, &fds)))
            continue;

        /* receive data */
        rcvlen = recv(skfd, &buf, sizeof(buf), 0);
        if (rcvlen > 0) {
            printf("%s\n", buf);
            // do something here!!!
            //
            //
            //
        }
    }

    close(skfd);
    return 0;
}

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <linux/netlink.h>

#define UEVENT_BUFFER_SIZE 2048

int thread_net_link()
{
	struct sockaddr_nl client;
	struct timeval tv;
	int skfd, rcvlen, ret;
	fd_set fds;
	int buffersize = 1024;

	skfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_KOBJECT_UEVENT);
	memset(&client, 0, sizeof(client)); 	   
	client.nl_family = AF_NETLINK;
	client.nl_pid = getpid(); 
	client.nl_groups = 1; /* receive broadcast message*/	
	setsockopt(skfd, SOL_SOCKET, SO_RCVBUF, &buffersize, sizeof(buffersize));
	bind(skfd, (struct sockaddr*)&client, sizeof(client));

	while (1) {
		char buf[UEVENT_BUFFER_SIZE] = { 0 };
		
		FD_ZERO(&fds);
		FD_SET(skfd, &fds);
		tv.tv_sec = 0;
		tv.tv_usec = 100 * 1000;
		ret = select(skfd + 1, &fds, NULL, NULL, &tv);
		if(ret < 0) 
			continue;
		if(!(ret > 0 && FD_ISSET(skfd, &fds)))
			continue;
			
		/* receive data */ 
		rcvlen = recv(skfd, &buf, sizeof(buf), 0);
		if (rcvlen > 0) {
			printf("%s\n", buf);
			// do something here!!!
			//
			//
			//
		}
	}  

	close(skfd);
	return 0;
}