Linux-内核通信之netlink机制-详解

用户空间：
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <string.h>
#include <asm/types.h>
#include <linux/netlink.h>
#include <linux/socket.h>
#include <errno.h>#define NETLINK_TEST 25
#define MAX_PAYLOAD 1024 // maximum payload sizeint sock_fd;
struct sockaddr_nl src_addr, dest_addr;
struct nlmsghdr *nlh = NULL;
struct iovec iov;
struct msghdr msg;void init_netlink()
{// Create a socketsock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);if(sock_fd == -1){printf("error getting socket: %s", strerror(errno));return;}// To prepare bindingmemset(&msg,0,sizeof(msg));memset(&src_addr, 0, sizeof(src_addr));//src_addresssrc_addr.nl_family = AF_NETLINK;src_addr.nl_pid = getpid(); // self pidsrc_addr.nl_groups = 0; // multi castbind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));//dest_addressmemset(&dest_addr, 0, sizeof(dest_addr));dest_addr.nl_family = AF_NETLINK;dest_addr.nl_pid = 0; /* For Linux Kernel */dest_addr.nl_groups = 0; /* unicast *//* Fill the netlink message header */nlh=(struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);nlh->nlmsg_pid = getpid(); /* self pid */nlh->nlmsg_flags = 0;/* Fill in the netlink message payload */strcpy(NLMSG_DATA(nlh), "connect to kernel");iov.iov_base = (void *)nlh;iov.iov_len = nlh->nlmsg_len;//iov.iov_len = NLMSG_SPACE(MAX_PAYLOAD);memset(&msg, 0, sizeof(msg));msg.msg_name = (void *)&dest_addr;msg.msg_namelen = sizeof(dest_addr);msg.msg_iov = &iov;msg.msg_iovlen = 1;
}int main(int argc, char* argv[])
{int state;int state_smg = 0;	init_netlink();printf(" Sending message. ...\n");state_smg = sendmsg(sock_fd,&msg,0);if(state_smg == -1){printf("get error sendmsg = %s\n",strerror(errno));}memset(nlh,0,NLMSG_SPACE(MAX_PAYLOAD));printf(" Waiting message. ...\n");// Read message from kernelwhile(1){printf("In while recvmsg\n");state = recvmsg(sock_fd, &msg, 0);if(state<0){printf("state<1");}printf("In while\n");printf("Received message: %s\n",(char *) NLMSG_DATA(nlh));}close(sock_fd);return 0;
}

内核空间：
#include <linux/init.h>
#include <linux/module.h>
#include <linux/timer.h>
#include <linux/time.h>
#include <linux/types.h>
#include <net/sock.h>
#include <net/netlink.h> #define NETLINK_TEST 25
#define MAX_MSGSIZE 1024int pid;
int err;
struct sock *nl_sk = NULL;
int flag = 0;
char str[100];int stringlength(char *s)
{int slen = 0;for(; *s; s++){slen++;}return slen;
}
void send_netlink_data(char *message)
{struct sk_buff *skb_1;struct nlmsghdr *nlh;int len = NLMSG_SPACE(MAX_MSGSIZE);int slen = 0;skb_1 = alloc_skb(len,GFP_KERNEL);if(!skb_1){printk(KERN_ERR "my_net_link:alloc_skb_1 error\n");}slen = stringlength(message);nlh = nlmsg_put(skb_1,0,0,0,MAX_MSGSIZE,0);NETLINK_CB(skb_1).pid = 0;NETLINK_CB(skb_1).dst_group = 0;memcpy(NLMSG_DATA(nlh),message,slen+1);printk("my_net_link:send = %d, message '%s'.\n",slen,(char *)NLMSG_DATA(nlh));netlink_unicast(nl_sk,skb_1,pid,MSG_DONTWAIT);
}
void recv_netlink_data(struct sk_buff *__skb)
{struct sk_buff *skb;struct nlmsghdr *nlh;//struct completion cmpl;int i=10;printk("net_link: data is ready to read.\n");skb = skb_get (__skb);if(skb->len >= NLMSG_SPACE(0)){nlh = nlmsg_hdr(skb);memcpy(str, NLMSG_DATA(nlh), sizeof(str));printk("Message received:%s\n",str) ;pid = nlh->nlmsg_pid;while(i--){//init_completion(&cmpl);//wait_for_completion_timeout(&cmpl,1 * HZ);send_netlink_data("From kernel messages!");}flag = 1;kfree_skb(skb);}
}// Initialize netlink
int netlink_init(void)
{nl_sk = netlink_kernel_create(&init_net, NETLINK_TEST, 1, recv_netlink_data, NULL, THIS_MODULE);if(!nl_sk){printk(KERN_ERR "my_net_link: create netlink socket error.\n");return 1;}printk("my_net_link_3: create netlink socket ok.\n");return 0;
}static void netlink_exit(void)
{if(nl_sk != NULL){sock_release(nl_sk->sk_socket);}printk("my_net_link: self module exited\n");
}module_init(netlink_init);
module_exit(netlink_exit);MODULE_AUTHOR("suntianyu");
MODULE_LICENSE("GPL");