netlink-exam-user-recv.c

通过这些实例

//application receiver: netlink-exam-user-recv.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>		//========================
#include <linux/netlink.h>	//========================

#define MAX_MSGSIZE 1024


int main(void)
{
/* struct sockaddr_nl
{
  sa_family_t    nl_family;
  unsigned short nl_pad;		//default is 0
  __u32          nl_pid;
  __u32          nl_groups;
};	

struct nlmsghdr		//为 netlink socket 自己的消息头，netlink 控制块
{
  __u32 nlmsg_len;   //Length of message 
  __u16 nlmsg_type;  // Message type
  __u16 nlmsg_flags; // Additional flags 
  __u32 nlmsg_seq;   // Sequence number 
  __u32 nlmsg_pid;   // Sending process PID 
};

*/
        struct sockaddr_nl saddr, daddr;
        struct nlmsghdr *nlhdr = NULL;
        struct msghdr msg;
        struct iovec iov;
        int sd;
        int ret = 1;

        sd = socket(AF_NETLINK, SOCK_RAW,NETLINK_GENERIC);	//===============
        memset(&saddr, 0, sizeof(saddr));
        memset(&daddr, 0, sizeof(daddr));

        saddr.nl_family = AF_NETLINK;      
        saddr.nl_pid = getpid();
        saddr.nl_groups = 1;
        bind(sd, (struct sockaddr*)&saddr, sizeof(saddr));	//===============


        nlhdr = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_MSGSIZE));//宏NLMSG_SPACE(len)返回不小于NLMSG_LENGTH(len)且字节对齐的最小数值，它也用于分配消息缓存

        while (1) {
                memset(nlhdr, 0, NLMSG_SPACE(MAX_MSGSIZE));

                iov.iov_base = (void *)nlhdr;
                iov.iov_len = NLMSG_SPACE(MAX_MSGSIZE);
                msg.msg_name = (void *)&daddr;
                msg.msg_namelen = sizeof(daddr);
                msg.msg_iov = &iov;
                msg.msg_iovlen = 1;

                ret = recvmsg(sd, &msg, 0);		//===========================
                if (ret == 0) {
                        printf("Exit.\n");
                        exit(0);
                }
                else if (ret == -1) {
                        perror("recvmsg:");
                        exit(1);
                }
		
                printf("%s", NLMSG_DATA(nlhdr));//宏NLMSG_DATA(nlh)用于取得消息的数据部分的首地址，设置和读取消息数据部分时需要使用该宏。

        }
 
        close(sd);		//======================================
}