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>
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/sched.h>
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#include <net/sock.h>
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#include <linux/netlink.h>
-
-
#define NETLINK_TEST 17
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struct {
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__u32 pid;
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}user_process;
-
-
static struct sock *netlinkfd = NULL;
-
-
int send_to_user(char *info) //发送到用户空间
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{
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int size;
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struct sk_buff *skb;
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unsigned char *old_tail;
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struct nlmsghdr *nlh; //报文头
-
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int retval;
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size = NLMSG_SPACE(strlen(info)); //报文大小
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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
-
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//初始化一个netlink消息首部
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nlh = nlmsg_put(skb, 0, 0, 0, NLMSG_SPACE(strlen(info))-sizeof(struct nlmsghdr), 0);
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old_tail = skb->tail;
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memcpy(NLMSG_DATA(nlh), info, strlen(info)); //填充数据区
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nlh->nlmsg_len = skb->tail - old_tail; //设置消息长度
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//设置控制字段
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NETLINK_CB(skb).pid = 0;
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NETLINK_CB(skb).dst_group = 0;
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printk(KERN_DEBUG "[kernel space] skb->data:%s\n", (char *)NLMSG_DATA((struct nlmsghdr *)skb->data));
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//发送数据
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retval = netlink_unicast(netlinkfd, skb, user_process.pid, MSG_DONTWAIT);
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printk(KERN_DEBUG "[kernel space] netlink_unicast return: %d\n", retval);
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return 0;
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}
-
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void kernel_receive(struct sk_buff *__skb) //内核从用户空间接收数据
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{
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struct sk_buff *skb;
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struct nlmsghdr *nlh = NULL;
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char *data = "This is eric's test message from kernel";
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printk(KERN_DEBUG "[kernel space] begin kernel_receive\n");
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skb = skb_get(__skb);
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if(skb->len >= sizeof(struct nlmsghdr)){
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nlh = (struct nlmsghdr *)skb->data;
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if((nlh->nlmsg_len >= sizeof(struct nlmsghdr))
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&& (__skb->len >= nlh->nlmsg_len)){
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user_process.pid = nlh->nlmsg_pid;
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printk(KERN_DEBUG "[kernel space] data receive from user are:%s\n", (char *)NLMSG_DATA(nlh));
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printk(KERN_DEBUG "[kernel space] user_pid:%d\n", user_process.pid);
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send_to_user(data);
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}
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}else{
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printk(KERN_DEBUG "[kernel space] data receive from user are:%s\n",(char *)NLMSG_DATA(nlmsg_hdr(__skb)));
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send_to_user(data);
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}
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kfree_skb(skb);
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}
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int __init test_netlink_init(void)
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{
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netlinkfd = netlink_kernel_create(&init_net, NETLINK_TEST, 0, kernel_receive, NULL, THIS_MODULE);
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if(!netlinkfd){
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printk(KERN_ERR "can not create a netlink socket\n");
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return -1;
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}
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return 0;
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}
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void __exit test_netlink_exit(void)
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{
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sock_release(netlinkfd->sk_socket);
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printk(KERN_DEBUG "test_netlink_exit!!\n");
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}
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module_init(test_netlink_init);
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module_exit(test_netlink_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("eric.hu");
用户空间程序代码:user_sent.c- #include <stdio.h>
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#include <stdlib.h>
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#include <sys/socket.h>
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#include <string.h>
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#include <linux/netlink.h>
-
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#define NETLINK_TEST 17
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#define MSG_LEN 100
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struct msg_to_kernel
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{
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struct nlmsghdr hdr;
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char data[MSG_LEN];
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};
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struct u_packet_info
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{
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struct nlmsghdr hdr;
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char msg[MSG_LEN];
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};
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int main(int argc, char* argv[])
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{
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char *data = "This message is from eric's space";
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//初始化
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struct sockaddr_nl local;
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struct sockaddr_nl kpeer;
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int skfd, ret, kpeerlen = sizeof(struct sockaddr_nl);
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struct nlmsghdr *message;
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struct u_packet_info info;
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char *retval;
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message = (struct nlmsghdr *)malloc(1);
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skfd = socket(PF_NETLINK, SOCK_RAW, NETLINK_TEST);
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if(skfd < 0){
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printf("can not create a netlink socket\n");
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return -1;
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}
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memset(&local, 0, sizeof(local));
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local.nl_family = AF_NETLINK;
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local.nl_pid = getpid();
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local.nl_groups = 0;
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if(bind(skfd, (struct sockaddr *)&local, sizeof(local)) != 0){
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printf("bind() error\n");
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return -1;
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}
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memset(&kpeer, 0, sizeof(kpeer));
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kpeer.nl_family = AF_NETLINK;
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kpeer.nl_pid = 0;
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kpeer.nl_groups = 0;
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memset(message, '\0', sizeof(struct nlmsghdr));
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message->nlmsg_len = NLMSG_SPACE(strlen(data));
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message->nlmsg_flags = 0;
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message->nlmsg_type = 0;
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message->nlmsg_seq = 0;
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message->nlmsg_pid = local.nl_pid;
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retval = memcpy(NLMSG_DATA(message), data, strlen(data));
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printf("message sendto kernel are:%s, len:%d\n", (char *)NLMSG_DATA(message), message->nlmsg_len);
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ret = sendto(skfd, message, message->nlmsg_len, 0,(struct sockaddr *)&kpeer, sizeof(kpeer));
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if(!ret){
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perror("send pid:");
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exit(-1);
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}
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//接受内核态确认信息
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ret = recvfrom(skfd, &info, sizeof(struct u_packet_info),0, (struct sockaddr*)&kpeer, &kpeerlen);
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if(!ret){
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perror("recv form kerner:");
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exit(-1);
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}
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printf("message receive from kernel:%s\n",(char *)info.msg);
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//内核和用户进行通信
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close(skfd);
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return 0;
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}
运行用户程序,输出结果如下:
- [root@FriendlyARM netlink]# ./user_sent
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message sendto kernel are:This message is from eric's space, len:52
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message receive from kernel:This is eric's test message from kernel
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