用户层与内核层通信 netlink

readme.md

用户层与内核层通信

1. make
2. 另开一个窗口 运行dmesg -w
3. insmod ktest.ko
4. ./utest

ktest.c

/**
 *	@file:	ktest.c
 *	@brief: kernel example
 *	@author: lflish
 *	@date: 2018-8-1
 *	@email:	hxy.gold@gmail.com
 *	kernel version:	3.10.0-862	
 **/

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

MODULE_LICENSE("GPL");
MODULE_AUTHOR("lflish");

#define MAX_MSGSIZE 125

#define NETLINK_TEST 30

struct sock *nl_sk = NULL;
//向用户空间发送消息的接口
int sendnlmsg(char *message,int pid)
{
    struct sk_buff *skb;
    struct nlmsghdr *nlh;

    int slen = 0;

    if(!message || !nl_sk){
        return -1;
    }

    slen = strlen(message);

    // 为新的 sk_buffer申请空间
    skb = nlmsg_new(slen, GFP_ATOMIC);
    if(!skb){
        printk(KERN_ERR "my_net_link: alloc_skb Error./n");
        return -2;
    }

    //用nlmsg_put()来设置netlink消息头部
    nlh = nlmsg_put(skb, 0, 0, NETLINK_TEST, slen, 0);
	if(nlh == NULL){
		printk("nlmsg_put failauer \n");
		nlmsg_free(skb);
		return -1;
	}

    memcpy(nlmsg_data(nlh), message, slen);

    //通过netlink_unicast()将消息发送用户空间由pid所指定了进程号的进程
    netlink_unicast(nl_sk, skb, pid, MSG_DONTWAIT);
    printk("send OK!\n");

    return 0;
}

static void nl_data_ready(struct sk_buff *skb)
{
    struct nlmsghdr *nlh = NULL;
    char *umsg = NULL;
    char kmsg[] = "hello users!!!";

    if(skb->len >= nlmsg_total_size(0))
    {   
        nlh = nlmsg_hdr(skb);
        umsg = NLMSG_DATA(nlh);
        if(umsg)
        {   
            printk("kernel recv from user: %s\n", umsg);
            sendnlmsg (kmsg, nlh->nlmsg_pid);
        }   
    }   
}

struct netlink_kernel_cfg cfg = {
	.input = nl_data_ready, /* set recv callback */
};

int myinit_module(void)
{
    printk("my netlink in\n");
    nl_sk = netlink_kernel_create(&init_net, NETLINK_TEST, &cfg);
	if(nl_sk == NULL)
		printk("kernel_create error\n");
    return 0;
}

void mycleanup_module(void)
{
    printk("my netlink out!\n");
    sock_release(nl_sk->sk_socket);
	netlink_kernel_release(nl_sk);
}

module_init(myinit_module);
module_exit(mycleanup_module);

Makefile

MODULE_NAME :=ktest
obj-m :=$(MODULE_NAME).o

KERNELDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)

all: user kernel

kernel:
    $(MAKE) -C $(KERNELDIR) M=$(PWD)

user: utest.c
    gcc utest.c -o utest

clean:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) clean
    rm -rf utest

utest.c

/**
 *	@file:	ktest.c
 *	@brief: kernel example
 *	@author: lflish
 *	@date: 2018-8-1
 *	@email:	hxy.gold@gmail.com	
 **/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>


/* /usr/include/linux/netlink.h */
#include <linux/netlink.h>

#define NETLINK_TEST 30
int main()
{
	/* 建立socket */
	int skfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);
	if(skfd == -1){
		perror("create socket error\n");
		return -1;
	}

	/* netlink socket */
	struct sockaddr_nl nladdr;
	
	/*init netlink socket */
	nladdr.nl_family = AF_NETLINK;	/* AF_NETLINK or PE_NETLINK */
	nladdr.nl_pad = 0;				/* not use */
	nladdr.nl_pid = 0;				/* 传送到内核 */
	nladdr.nl_groups = 0;			/* 单播*/
	
	/* bing 绑定netlink socket 与socket */
	if( 0 != bind(skfd, (struct sockaddr *)&nladdr, sizeof(struct sockaddr_nl))){
		perror("bind() error\n");
		close(skfd);
		return -1;
	}

	/* 构造msg消息*/
	struct msghdr msg;
	memset(&msg, 0, sizeof(msg));
	msg.msg_name = (void *)&(nladdr);
	msg.msg_namelen = sizeof(nladdr);

	#define MAX_MSGSIZE 1024
	char buffer[] = "hello kernel!!!";

	/* netlink 消息头 */
	struct nlmsghdr *nlhdr;
	nlhdr = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_MSGSIZE));

	strcpy(NLMSG_DATA(nlhdr),buffer);

	nlhdr->nlmsg_len = NLMSG_LENGTH(strlen(buffer));
	nlhdr->nlmsg_pid = getpid();  /* self pid */
	nlhdr->nlmsg_flags = 0;


	struct iovec iov;

	iov.iov_base = (void *)nlhdr;
	iov.iov_len = nlhdr->nlmsg_len;
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
		
	sendmsg(skfd, &msg, 0);

	/* recv */
	//memset((char *)NLMSG_DATA(nlhdr), 0, 1024);
	recvmsg(skfd, &msg, 0);

	printf("kernel: %s\n", NLMSG_DATA(nlhdr));
	//printf("kernel: %s\n", nlmsg_data(nlhdr));

	close(skfd);
	free(nlhdr);

	return 0;
}