Netlink套接字

原帖地址：http://tcspecial.iteye.com/blog/2174781

Linux下如何实现用户态与内核态的交互呢？一种是上文讲的/proc文件，还有一种是netlink套接字机制，netlink实现了用户空间与内核空间双向通信方法。

netlink用户态API与常见的socket编程一致，只是内核态要实现自定义protocol。

 

一.内核态模块

    该模块用于接收用户态信息，并发送一字符串响应。

#ifndef __KERNEL__
#define __KERNEL__
#endif  /* __KERNEL__ */

#include
#include
#include
#include
#include
#include
#include
#include   // netlink
#include
#include

#define NETLINK_TEST 31    // 自定义用户协议

static struct sock *nlfd = NULL;  // 内核socket文件描述符
static char *payload = "Hello user,i'm from kernel!";

// 向用户层发送消息
static int sendNLMsg(int pid,void *msg,int len)
{
    struct sk_buff *skb;
    int size,count;
    struct nlmsghdr *nlmsgh = NULL;
    char *pos = NULL;
    int retval = 0;

    size = NLMSG_SPACE(len);               // 加消息头部长度
    skb = alloc_skb(size,GFP_KERNEL);   // 申请空间
    if(!skb)
    {
        retval = -1;
        return retval;
    }

    nlmsgh = nlmsg_put(skb,0,0,0,len,0);

    // 填充数据
    pos = NLMSG_DATA(nlmsgh);
    memset(pos,0,len);
    memcpy(pos,msg,len);

    NETLINK_CB(skb).dst_group = 0;  // 单播

    count = netlink_unicast(nlfd,skb,pid,MSG_DONTWAIT);
    printk(KERN_ALERT "pid:%d send:%d\n",pid,count);

    return retval;
}


// 处理用户层传递的消息
static void handle_msg(struct sk_buff *_sk)
{
    struct sk_buff *skb;
    struct nlmsghdr *nlh = NULL;
    char str[100] = {};
    int pid;

    printk("==>handle_msg\n");

    skb = skb_get(_sk);   // 引用当前_sk

    if(skb->len >= NLMSG_SPACE(0))
    {
        nlh = nlmsg_hdr(skb);         // 获得信息头部
        pid = nlh->nlmsg_pid;         // 获取用户进程pid

        memcpy(str,NLMSG_DATA(nlh),100);
        printk(KERN_ERR "recv:%s\n",str);

        sendNLMsg(pid,payload,strlen(payload));  // 向用户层发送数据

        kfree_skb(skb);
    }

    printk("<==handle_msg\n");
}

// 建立netlink套接字
int NLCreate(void)
{
        // 消息回调函数为handle_msg，注：参数1区别以往内核版本API，设为init_net
    nlfd = netlink_kernel_create(&init_net,NETLINK_TEST,1,handle_msg,NULL,THIS_MODULE);
    if(!nlfd)
    {
        return -1;
    }

    return 0;
}

// 清除netlink套接字
int NLDestroy(void)
{
    if(nlfd)
    {
        sock_release(nlfd->sk_socket);
    }

    return 0;
}


static int __init netlink_init(void)
{
    NLCreate();

    return 0;
}


static void __exit netlink_exit(void)
{
    NLDestroy();
}

module_init(netlink_init);
module_exit(netlink_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("kettas");
MODULE_DESCRIPTION("Netlink Test Demo");
MODULE_VERSION("1.0.1");
MODULE_ALIAS("Netlink 01");

#ifndef __KERNEL__
#define __KERNEL__
#endif  /* __KERNEL__ */

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include   // netlink 
#include 
#include 

#define NETLINK_TEST 31    // 自定义用户协议 

static struct sock *nlfd = NULL;  // 内核socket文件描述符
static char *payload = "Hello user,i'm from kernel!";

// 向用户层发送消息
static int sendNLMsg(int pid,void *msg,int len)
{
	struct sk_buff *skb;
	int size,count;
	struct nlmsghdr *nlmsgh = NULL;
	char *pos = NULL;
	int retval = 0;

	size = NLMSG_SPACE(len);               // 加消息头部长度
	skb = alloc_skb(size,GFP_KERNEL);	// 申请空间
	if(!skb)
	{
		retval = -1;
		return retval;
	}

	nlmsgh = nlmsg_put(skb,0,0,0,len,0);

	// 填充数据
	pos = NLMSG_DATA(nlmsgh);
	memset(pos,0,len);
	memcpy(pos,msg,len);

	NETLINK_CB(skb).dst_group = 0;  // 单播

	count = netlink_unicast(nlfd,skb,pid,MSG_DONTWAIT); 
	printk(KERN_ALERT "pid:%d send:%d\n",pid,count);

	return retval;
}


// 处理用户层传递的消息
static void handle_msg(struct sk_buff *_sk)
{
	struct sk_buff *skb;
	struct nlmsghdr *nlh = NULL;
	char str[100] = {};
	int pid;

 	printk("==>handle_msg\n");
 	
 	skb = skb_get(_sk);   // 引用当前_sk

 	if(skb->len >= NLMSG_SPACE(0))
 	{
 		nlh = nlmsg_hdr(skb);  	      // 获得信息头部
 		pid = nlh->nlmsg_pid;         // 获取用户进程pid

 		memcpy(str,NLMSG_DATA(nlh),100);
 		printk(KERN_ERR "recv:%s\n",str);

 		sendNLMsg(pid,payload,strlen(payload));  // 向用户层发送数据

 		kfree_skb(skb);
 	}

 	printk("<==handle_msg\n");
}

// 建立netlink套接字
int NLCreate(void)
{
        // 消息回调函数为handle_msg，注：参数1区别以往内核版本API，设为init_net
 	nlfd = netlink_kernel_create(&init_net,NETLINK_TEST,1,handle_msg,NULL,THIS_MODULE);
	if(!nlfd)
	{
		return -1;
	}

	return 0;
}

// 清除netlink套接字
int NLDestroy(void)
{
	if(nlfd)
	{
		sock_release(nlfd->sk_socket);
	}

	return 0;
}


static int __init netlink_init(void)
{
	NLCreate();

	return 0;
}


static void __exit netlink_exit(void)
{
	NLDestroy();
}

module_init(netlink_init);
module_exit(netlink_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("kettas");
MODULE_DESCRIPTION("Netlink Test Demo");
MODULE_VERSION("1.0.1");
MODULE_ALIAS("Netlink 01");

 

 

二.用户态

该应用向内核模块发送信息，并接收来自内核响应字符串。

        

#include
#include
#include
#include
#include
#include
#include
#include


#define NETLINK_TEST 31
#define MAX_NL_MSG_LEN 1024

typedef struct _packet_u
{
    struct nlmsghdr hdr;
    char payload[1024];
}packet_u;


static int nls;  // socket文件描述符

// 向内核发送消息
int sendtokernel(char *buf,int len,int type)
{
    struct nlmsghdr nlmsg;
    struct sockaddr_nl nldest = {};
    int size;

    nldest.nl_family    = AF_NETLINK;
    nldest.nl_pid       = 0;
    nldest.nl_groups    = 0;

    // 填充netlink消息头
    nlmsg.nlmsg_len = NLMSG_LENGTH(len);
    nlmsg.nlmsg_pid = getpid();
    nlmsg.nlmsg_flags = 0;
    nlmsg.nlmsg_type  = type;

    // 填充负载
    memcpy(NLMSG_DATA(&nlmsg),buf,len);

    // 发送
    size = sendto(nls,&nlmsg,nlmsg.nlmsg_len,0,(struct sockaddr*)&nldest,sizeof(nldest));
    return size;
}


// 接收内核消息
int recvfromkernel(void)
{
    int size = 0;

        // 方法一：调用recvfrom方法接收内核数据，注此时message结构体包含有消息体
        /*
    packet_u message;
    struct sockaddr_nl nldest = {};
    int len = sizeof(nldest);

    memset(&message,0,sizeof(message));

    nldest.nl_family    = AF_NETLINK;
    nldest.nl_pid       = 0;
    nldest.nl_groups    = 0;

    // 接收消息
    size = recvfrom(nls,
            &message,
            sizeof(message),
            0,
            (struct sockaddr*)&nldest,
            &len);
    printf("size:%d recv:%s\n",size,message.payload);   // NLMSG_DATA()与message.payload结果一致
        */
    // 方法二：调用recvmsg方法
    struct sockaddr_nl nladdr;
    struct msghdr msg;
    struct iovec iov;
    struct nlmsghdr *nlhdr;

    nlhdr = (struct nlmsghdr *)malloc(MAX_NL_MSG_LEN);
    iov.iov_base = (void *)nlhdr;
    iov.iov_len = MAX_NL_MSG_LEN;
    msg.msg_name = (void *)&(nladdr);
    msg.msg_namelen = sizeof(nladdr);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
    size = recvmsg(nls, &msg, 0);
    printf("size:%d recv:%s\n",size,(char*)NLMSG_DATA(nlhdr));

    return size;
}

int main(int argc,char **argv)
{
    struct sockaddr_nl nlsource;
    int ret;

    // socket
    nls = socket(PF_NETLINK,SOCK_RAW,NETLINK_TEST);
    assert(nls!=-1);

    memset(&nlsource,0,sizeof(struct sockaddr_nl));
    nlsource.nl_family = AF_NETLINK;
    nlsource.nl_pid    = getpid();
    nlsource.nl_groups = 0;

    // bind
    ret = bind(nls,(struct sockaddr*)&nlsource,sizeof(nlsource));
    assert(ret!=-1);

    // send
    char *str = "Hello kernel,i'm from user";
    sendtokernel(str,strlen(str),0);

    // recv
    recvfromkernel();

    close(nls);
    return 0;
}

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 


#define NETLINK_TEST 31
#define MAX_NL_MSG_LEN 1024

typedef struct _packet_u
{
	struct nlmsghdr hdr;
	char payload[1024];
}packet_u;


static int nls;  // socket文件描述符

// 向内核发送消息
int sendtokernel(char *buf,int len,int type)
{
	struct nlmsghdr nlmsg;
	struct sockaddr_nl nldest = {};
	int size;

	nldest.nl_family	= AF_NETLINK;
	nldest.nl_pid		= 0;
	nldest.nl_groups	= 0;

	// 填充netlink消息头
	nlmsg.nlmsg_len = NLMSG_LENGTH(len);
	nlmsg.nlmsg_pid = getpid();
	nlmsg.nlmsg_flags = 0;
	nlmsg.nlmsg_type  = type;

	// 填充负载
	memcpy(NLMSG_DATA(&nlmsg),buf,len);

	// 发送
	size = sendto(nls,&nlmsg,nlmsg.nlmsg_len,0,(struct sockaddr*)&nldest,sizeof(nldest));
	return size;
}


// 接收内核消息
int recvfromkernel(void)
{
	int size = 0;

        // 方法一：调用recvfrom方法接收内核数据，注此时message结构体包含有消息体
        /*
	packet_u message;
	struct sockaddr_nl nldest = {};
	int len = sizeof(nldest);
	
	memset(&message,0,sizeof(message));

	nldest.nl_family	= AF_NETLINK;
	nldest.nl_pid		= 0;
	nldest.nl_groups	= 0;
	
	// 接收消息
	size = recvfrom(nls, 
			&message, 
			sizeof(message), 
			0, 
			(struct sockaddr*)&nldest, 
			&len);	
	printf("size:%d recv:%s\n",size,message.payload);   // NLMSG_DATA()与message.payload结果一致				
        */
	// 方法二：调用recvmsg方法
	struct sockaddr_nl nladdr;
	struct msghdr msg;
	struct iovec iov;
	struct nlmsghdr *nlhdr;

	nlhdr = (struct nlmsghdr *)malloc(MAX_NL_MSG_LEN);
	iov.iov_base = (void *)nlhdr;
	iov.iov_len = MAX_NL_MSG_LEN;
	msg.msg_name = (void *)&(nladdr);
	msg.msg_namelen = sizeof(nladdr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	size = recvmsg(nls, &msg, 0);
	printf("size:%d recv:%s\n",size,(char*)NLMSG_DATA(nlhdr));

	return size;
}

int main(int argc,char **argv)
{
	struct sockaddr_nl nlsource;
	int ret;

	// socket
	nls = socket(PF_NETLINK,SOCK_RAW,NETLINK_TEST);
	assert(nls!=-1);

	memset(&nlsource,0,sizeof(struct sockaddr_nl));
	nlsource.nl_family = AF_NETLINK;
	nlsource.nl_pid	   = getpid();
	nlsource.nl_groups = 0;

	// bind
	ret = bind(nls,(struct sockaddr*)&nlsource,sizeof(nlsource));
	assert(ret!=-1);

	// send
	char *str = "Hello kernel,i'm from user";
	sendtokernel(str,strlen(str),0);

	// recv
	recvfromkernel();

	close(nls);
	return 0;
}

 

三.测试运行

 

[scada@linux netlink]$ sudo insmod netlink_test.ko
[scada@linux netlink]$ ./netlink_u
size:44 recv:Hello user,i'm from kernel!
[scada@linux netlink]$ dmesg
==>handle_msg
recv:Hello kernel,i'm from user
pid:40122 send:44
<==handle_msg