netlink socket编程实例

http://blog.chinaunix.net/uid-14753126-id-2983915.html

 netlink socket编程实例 2011-10-31 13:02:06

分类： LINUX

关于Netlink IPC方式的介绍，请参见http://blog.chinaunix.net/space.php?uid=14753126&do=blog&id=2978566
本文通过一个编程实例来更深入地了解netlink。
功能描述：
1. 本实例包含2个部分：内核模块和用户程序
2.用户程序通过netlink socket建立与kernel module连接，并向kernel module发送一条信息。
3.内核在接收到用户的信息后，向用户程序发送一条确认信息。

说明：对于不知如何编译内核模块以及用户程序的童鞋请google

内核模块代码(test_netlink_kmodule.c)：

 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/sched.h>
 #include <net/sock.h>
 #include <linux/netlink.h>

 #define NETLINK_TEST 17
 struct {
     __u32 pid;
 }user_process;

 static struct sock *netlinkfd = NULL;

 int send_to_user(char *info) //发送到用户空间
 {
     int size;
     struct sk_buff *skb;
     unsigned char *old_tail;
     struct nlmsghdr *nlh; //报文头

     int retval;

     size = NLMSG_SPACE(strlen(info)); //报文大小
     skb = alloc_skb(size, GFP_ATOMIC); //分配一个新的套接字缓存,使用GFP_ATOMIC标志进程不>会被置为睡眠

     //初始化一个netlink消息首部
     nlh = nlmsg_put(skb, 0, 0, 0, NLMSG_SPACE(strlen(info))-sizeof(struct nlmsghdr), 0);
     old_tail = skb->tail;
     memcpy(NLMSG_DATA(nlh), info, strlen(info)); //填充数据区
     nlh->nlmsg_len = skb->tail - old_tail; //设置消息长度

     //设置控制字段
     NETLINK_CB(skb).pid = 0;
     NETLINK_CB(skb).dst_group = 0;

     printk(KERN_DEBUG "[kernel space] skb->data:%s\n", (char *)NLMSG_DATA((struct nlmsghdr *)skb->data));

     //发送数据
     retval = netlink_unicast(netlinkfd, skb, user_process.pid, MSG_DONTWAIT);
     printk(KERN_DEBUG "[kernel space] netlink_unicast return: %d\n", retval);
     return 0;
 }

 void kernel_receive(struct sk_buff *__skb) //内核从用户空间接收数据
 {
     struct sk_buff *skb;
     struct nlmsghdr *nlh = NULL;

     char *data = "This is eric's test message from kernel";

     printk(KERN_DEBUG "[kernel space] begin kernel_receive\n");
     skb = skb_get(__skb);

     if(skb->len >= sizeof(struct nlmsghdr)){
         nlh = (struct nlmsghdr *)skb->data;
         if((nlh->nlmsg_len >= sizeof(struct nlmsghdr))
             && (__skb->len >= nlh->nlmsg_len)){
             user_process.pid = nlh->nlmsg_pid;
             printk(KERN_DEBUG "[kernel space] data receive from user are:%s\n", (char *)NLMSG_DATA(nlh));
             printk(KERN_DEBUG "[kernel space] user_pid:%d\n", user_process.pid);
             send_to_user(data);
         }
     }else{
         printk(KERN_DEBUG "[kernel space] data receive from user are:%s\n",(char *)NLMSG_DATA(nlmsg_hdr(__skb)));
         send_to_user(data);
     }

     kfree_skb(skb);
 }

 int __init test_netlink_init(void)
 {

     netlinkfd = netlink_kernel_create(&init_net, NETLINK_TEST, 0, kernel_receive, NULL, THIS_MODULE);
     if(!netlinkfd){
         printk(KERN_ERR "can not create a netlink socket\n");
         return -1;
     }
     return 0;
 }

 void __exit test_netlink_exit(void)
 {
     sock_release(netlinkfd->sk_socket);
     printk(KERN_DEBUG "test_netlink_exit!!\n");
 }

 module_init(test_netlink_init);
 module_exit(test_netlink_exit);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("eric.hu");

用户空间程序代码：user_sent.c

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

 #define NETLINK_TEST 17
 #define MSG_LEN 100

 struct msg_to_kernel
 {
     struct nlmsghdr hdr;
     char data[MSG_LEN];
 };
 struct u_packet_info
 {
     struct nlmsghdr hdr;
     char msg[MSG_LEN];
 };

 int main(int argc, char* argv[])
 {
     char *data = "This message is from eric's space";
     //初始化
     struct sockaddr_nl local;
     struct sockaddr_nl kpeer;
     int skfd, ret, kpeerlen = sizeof(struct sockaddr_nl);
     struct nlmsghdr *message;
     struct u_packet_info info;
     char *retval;
     message = (struct nlmsghdr *)malloc(1);

     skfd = socket(PF_NETLINK, SOCK_RAW, NETLINK_TEST);
     if(skfd < 0){
         printf("can not create a netlink socket\n");
         return -1;
     }
     memset(&local, 0, sizeof(local));
     local.nl_family = AF_NETLINK;
     local.nl_pid = getpid();
     local.nl_groups = 0;
     if(bind(skfd, (struct sockaddr *)&local, sizeof(local)) != 0){
         printf("bind() error\n");
         return -1;
     }
     memset(&kpeer, 0, sizeof(kpeer));
     kpeer.nl_family = AF_NETLINK;
     kpeer.nl_pid = 0;
     kpeer.nl_groups = 0;

     memset(message, '\0', sizeof(struct nlmsghdr));
     message->nlmsg_len = NLMSG_SPACE(strlen(data));
     message->nlmsg_flags = 0;
     message->nlmsg_type = 0;
     message->nlmsg_seq = 0;
     message->nlmsg_pid = local.nl_pid;

     retval = memcpy(NLMSG_DATA(message), data, strlen(data));

     printf("message sendto kernel are:%s, len:%d\n", (char *)NLMSG_DATA(message), message->nlmsg_len);
     ret = sendto(skfd, message, message->nlmsg_len, 0,(struct sockaddr *)&kpeer, sizeof(kpeer));
     if(!ret){
         perror("send pid:");
         exit(-1);
     }

     //接受内核态确认信息
     ret = recvfrom(skfd, &info, sizeof(struct u_packet_info),0, (struct sockaddr*)&kpeer, &kpeerlen);
     if(!ret){
         perror("recv form kerner:");
         exit(-1);
     }

     printf("message receive from kernel:%s\n",(char *)info.msg);
     //内核和用户进行通信

     close(skfd);
     return 0;
 }

运行用户程序，输出结果如下：

 [root@FriendlyARM netlink]# ./user_sent
 message sendto kernel are:This message is from eric's space, len:52
 message receive from kernel:This is eric's test message from kernel