netlink实例 | 易学教程

#include <linux/module.h>
#include <linux/netlink.h>
#include <net/netlink.h>
#include <net/net_namespace.h>
#define NETLINK_TEST 31

#define NLMSG_SETECHO 0x11
#define NLMSG_GETECHO 0x12

static struct sock *sk; //内核端socket
static void nl_custom_data_ready(struct sk_buff *skb); //接收消息回调函数

int __init nl_custom_init(void)
{
struct netlink_kernel_cfg nlcfg = {
.input = nl_custom_data_ready,
};
sk = netlink_kernel_create(&init_net, NETLINK_TEST, &nlcfg);
printk(KERN_INFO "initialed ok!\n");
if (!sk) {
printk(KERN_INFO "netlink create error!\n");
}
return 0;
}
void __exit nl_custom_exit(void)
{
printk(KERN_INFO "existing...\n");
netlink_kernel_release(sk);
}

static void nl_custom_data_ready(struct sk_buff *skb)
{
struct nlmsghdr *nlh;
void *payload;
struct sk_buff *out_skb;
void *out_payload;
struct nlmsghdr *out_nlh;
int payload_len; // with padding, but ok for echo
nlh = nlmsg_hdr(skb);
switch(nlh->nlmsg_type)
{
case NLMSG_SETECHO:
break;
case NLMSG_GETECHO:
payload = nlmsg_data(nlh);
payload_len = nlmsg_len(nlh);
printk(KERN_INFO "payload_len = %d\n", payload_len);
printk(KERN_INFO "Recievid: %s, From: %d\n", (char *)payload, nlh->nlmsg_pid);
out_skb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL); //分配足以存放默认大小的sk_buff
if (!out_skb) goto failure;
out_nlh = nlmsg_put(out_skb, 0, 0, NLMSG_SETECHO, payload_len, 0); //填充协议头数据
if (!out_nlh) goto failure;
out_payload = nlmsg_data(out_nlh);
strcpy(out_payload, "[from kernel]:"); // 在响应中加入字符串，以示区别
strcat(out_payload, payload);
nlmsg_unicast(sk, out_skb, nlh->nlmsg_pid);
break;
default:
printk(KERN_INFO "Unknow msgtype recieved!\n");
}
return;
failure:
printk(KERN_INFO " failed in fun dataready!\n");
}
module_init(nl_custom_init);
module_exit(nl_custom_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("a simple example for custom netlink protocal family");
MODULE_AUTHOR("RSLjdkt");

用户

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <linux/netlink.h>
#include <sys/socket.h>
#include <strings.h>
#include <string.h>
#define NETLINK_TEST 31 // 自定义的协议号
/** 消息类型 **/
#define NLMSG_SETECHO 0x11
#define NLMSG_GETECHO 0x12
/** 最大协议负荷(固定) **/
#define MAX_PAYLOAD 101

struct sockaddr_nl src_addr, dst_addr;
struct iovec iov;
int sockfd;
struct nlmsghdr *nlh = NULL;
struct msghdr msg;

int main( int argc, char **argv)
{
if (argc != 2) {
printf("usage: ./a.out <str>\n");
exit(-1);
}

sockfd = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_TEST); // 创建NETLINK_TEST协议的socket
/* 设置本地端点并绑定，用于侦听 */
bzero(&src_addr, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid();
src_addr.nl_groups = 0; //未加入多播组
bind(sockfd, (struct sockaddr*)&src_addr, sizeof(src_addr));
/* 构造目的端点，用于发送 */
bzero(&dst_addr, sizeof(dst_addr));
dst_addr.nl_family = AF_NETLINK;
dst_addr.nl_pid = 0; // 表示内核
dst_addr.nl_groups = 0; //未指定接收多播组
/* 构造发送消息 */
nlh = (struct nlmsghdr *) malloc(NLMSG_SPACE(MAX_PAYLOAD));
nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD); //保证对齐
nlh->nlmsg_pid = getpid(); /* self pid */
nlh->nlmsg_flags = 0;
nlh->nlmsg_type = NLMSG_GETECHO;
strcpy((char *)NLMSG_DATA(nlh), argv[1]);
iov.iov_base = (void *)nlh;
iov.iov_len = nlh->nlmsg_len;
msg.msg_name = (void *)&dst_addr;
msg.msg_namelen = sizeof(dst_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;

sendmsg(sockfd, &msg, 0); // 发送
/* 接收消息并打印 */
memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
recvmsg(sockfd, &msg, 0);
printf(" Received message payload: %s\n",
(char *) NLMSG_DATA(nlh));
   printf(" Received message payload: %s %lx %lx\n",
(char *) NLMSG_DATA(nlh) ,msg.msg_iov->iov_len
,(unsigned long)((struct nlmsghdr *)msg.msg_iov->iov_base)->nlmsg_len);
}

来源：CSDN

作者：NeiborGirl

链接：https://blog.csdn.net/qq_31105785/article/details/104348588

标签

netlink