netlink 通信广播demo

最近在做工程时，用到了内核间通信，需要把内核部分得到发送至用户空间。下面给出demo例子：

分为内核部分和用户空间部分：

首先在内核部分增加一个netlink消息类型

#define NETLINK_URL			23

创建内核的netlink socket

1. static struct sock *nlfd;

2.  
3.  

4. struct netlink_kernel_cfg cfg = {

5. .groups = 1, //组播标识，当前只有1个组

6. .input = netlink_receive,//接收回调函数

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7. };

8.  

9. nlfd = netlink_kernel_create(net, NETLINK_URL, &cfg);

10. if (nlfd == NULL) {

11. printk(KERN_INFO "netlink kernel create failed\n");

12. return -ENOMEM;

13. }

向用户空间广播报文

1. int send_urlinfo_to_usrspace(struct sk_buff *skb, char *url)

2. {

3. struct sk_buff *info;

4. struct nlmsghdr *nlh;

5. struct packet_info *data;

6. int ret;

7.  

8. if(unlikely(nlfd== NULL))

9. return 0;

10.  

11. if (!netlink_has_listeners(nlfd, 1))

12. return 0;

13.  

14. info = alloc_skb(NLMSG_SPACE(PACKET_INFO_PAYLOAD),GFP_ATOMIC);

15. if(info == NULL)

16. return;

17.  

18. skb_put(info, NLMSG_SPACE(PACKET_INFO_PAYLOAD));

19.  

20. nlh = (struct nlmsghdr *)info->data;

21. nlh->nlmsg_len = NLMSG_SPACE(PACKET_INFO_PAYLOAD);

22. nlh->nlmsg_pid = 0;

23. nlh->nlmsg_flags = 0;

24. data = NLMSG_DATA(nlh);

25. memset(data, 0, sizeof(struct packet_info));

26. strncpy(data->url, url, sizeof(data->url));

27.  

28. fill_mac_and_ip(skb, info);

29.  

30. ret = netlink_broadcast(nlfd, info, 0, 1, GFP_ATOMIC);

31.  

32. debug("send_urlinfo_to_usrspace, ret = %d, %d, %s\n", ret, info->len, url);

33.  

34. return ret;

35. }

接收用户空间的报文

1. static void netlink_receive(struct sk_buff *skb)

2. {

3. int ret;

4. mutex_lock(&receive_mutex);

5. ret = netlink_rcv_skb(skb, &user_rcv_msg);

6. mutex_unlock(&receive_mutex);

7. }

1. static int user_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)

2. {

3. struct packet_info *data;

4. int err, len;

5.  

6. nlh = nlmsg_hdr(skb);

7. len = skb->len;

8.  

9. data = nlmsg_data(nlh);

10.  

11. switch (nlh->nlmsg_type)

12. {

13. case ADD_URL:

14. if (nlmsg_len(nlh) < sizeof(struct packet_info))

15. return -EINVAL;

16. err = process_usr_info(data->url, strlen(data->url), data->blacklist);

17. break;

18. default:

19. printk(KERN_INFO "recv type error = %d\n", nlh->nlmsg_type);

20. err = -EINVAL;

21. break;

22. }

23.  

24. return err;

25. }

用户空间代码：

创建netlink socket，并绑定

1. if((nlsock = socket(PF_NETLINK, SOCK_RAW, NETLINK_URL)) < 0) {

2. printf( "Unable to create apmon socket: %s\n", strerror(errno));

3. return -1;

4. }

5.  

6. memset(&addr, 0, sizeof(addr));

7. addr.nl_family = AF_NETLINK;

8. addr.nl_pid = 0;

9. addr.nl_groups = 1;

10. if (bind(nlsock, (struct sockaddr*)&addr, sizeof(addr)) < 0) {

11. perror("bind");

12. }

接收部分，报文缓存在pbf中

1. static int netlink_recv(void *pbf, int maxlen)

2. {

3. struct sockaddr_nl dest_addr;

4. struct iovec iov;

5. struct msghdr hdr;

6.  

7. memset(pbf, 0, sizeof(struct nlmsghdr) + sizeof(struct packet_info));

8. memset(&dest_addr, 0, sizeof(dest_addr));

9. memset(&iov, 0, sizeof(iov));

10. memset(&hdr, 0, sizeof(hdr));

11.  

12. iov.iov_base = pbf;

13. iov.iov_len = maxlen;

14. hdr.msg_name = (void *)&dest_addr;

15. hdr.msg_namelen = sizeof(dest_addr);

16. hdr.msg_iov = &iov;

17. hdr.msg_iovlen = 1;

18.  

19. return recvmsg(nlsock, &hdr, 0);

20. }

发送报文至内核

1. struct nlmsghdr nlh = {0};

2. struct sockaddr_nl snl;

3. memset (&snl, 0, sizeof snl);

4. snl.nl_family = AF_NETLINK;

5.  

6. struct req req_ = {0};

7.  

8. req_.nlh.nlmsg_len = sizeof(struct req);

9. req_.nlh.nlmsg_type = 0x11;

10. req_.nlh.nlmsg_flags = NLM_F_REQUEST;

11. req_.nlh.nlmsg_pid = 0;

12. req_.nlh.nlmsg_seq = 0;

13.  

14. req_.info.blacklist = 0;

15. strcpy(req_.info.url, r->info.url);

16.  

17. ret = sendto(nlsock, (void*)&req_, sizeof(struct req), 0 , (struct sockaddr *) &snl, sizeof snl);

18. if (ret < 0)

19. perror("sendto");

20. else printf("send len %d\n", ret);