Linux 内核态 Socket 编程

1.内核态 socket API

内核态socket编程的过程和用户态下的socket编程流程一样，但是接口不同。Kernel提供了一组内核态的socket API，基本上在用户态的sockt API在内核中都有对应的API。 在net/socket.c中可以看到如下导出符号：

EXPORT_SYMBOL(kernel_sendmsg);  
EXPORT_SYMBOL(kernel_recvmsg);  
EXPORT_SYMBOL(sock_create_kern);  
EXPORT_SYMBOL(sock_release);  
EXPORT_SYMBOL(kernel_bind);  
EXPORT_SYMBOL(kernel_listen);  
EXPORT_SYMBOL(kernel_accept);  
EXPORT_SYMBOL(kernel_connect);  
EXPORT_SYMBOL(kernel_getsockname);  
EXPORT_SYMBOL(kernel_getpeername);  
EXPORT_SYMBOL(kernel_getsockopt);  
EXPORT_SYMBOL(kernel_setsockopt);  
EXPORT_SYMBOL(kernel_sendpage);  
EXPORT_SYMBOL(kernel_sock_ioctl);  
EXPORT_SYMBOL(kernel_sock_shutdown); 

下面以两个内核模块间利用socket进行通信为例来讲述内核态下socket编程。

server内核模块功能是：建立套接字，绑定端口，监听端口，等待client的连接，并接收client发来的数据。

client内核模块功能是：建立套接字，和server建立连接，并向server发送数据。

2. server模块

/*server.c*/
#include
#include
#include
#include

#include
#include

int myserver(void){

        struct socket *sock,*client_sock;
        struct sockaddr_in s_addr;
        unsigned short portnum=0x8888;
        int ret=0;

        memset(&s_addr,0,sizeof(s_addr));
        s_addr.sin_family=AF_INET;
        s_addr.sin_port=htons(portnum);
        s_addr.sin_addr.s_addr=htonl(INADDR_ANY);


        sock=(struct socket *)kmalloc(sizeof(struct socket),GFP_KERNEL);
        client_sock=(struct socket *)kmalloc(sizeof(struct socket),GFP_KERNEL);

        /*create a socket*/
        ret=sock_create_kern(AF_INET, SOCK_STREAM,0,&sock);
        if(ret){
                printk("server:socket_create error!\n");
        }
        printk("server:socket_create ok!\n");

        /*bind the socket*/
        ret=sock->ops->bind(sock,(struct sockaddr *)&s_addr,sizeof(struct sockaddr_in));
        if(ret<0){
                printk("server: bind error\n");
                return ret;
        }
        printk("server:bind ok!\n");

        /*listen*/
        ret=sock->ops->listen(sock,10);
        if(ret<0){
                printk("server: listen error\n");
                return ret;
        }
        printk("server:listen ok!\n");

        ret=sock->ops->accept(sock,client_sock,10);if(ret<0){
                printk("server:accept error!\n");
                return ret;
        }

        printk("server: accept ok, Connection Established\n");

        /*kmalloc a receive buffer*/
        char *recvbuf=NULL;
        recvbuf=kmalloc(1024,GFP_KERNEL);
        if(recvbuf==NULL){
                printk("server: recvbuf kmalloc error!\n");
                return -1;
        }
        memset(recvbuf, 0, sizeof(recvbuf));

        /*receive message from client*/
        struct kvec vec;
        struct msghdr msg;
        memset(&vec,0,sizeof(vec));
        memset(&msg,0,sizeof(msg));
        vec.iov_base=recvbuf;
        vec.iov_len=1024;
        ret=kernel_recvmsg(client_sock,&msg,&vec,1,1024,0); /*receive message*/
        printk("receive message:\n %s\n",recvbuf);
        
	/*release socket*/
	sock_release(sock);
        sock_release(client_sock);
        return ret;
}

static int server_init(void){
        printk("server init:\n");
        return (myserver());
}

static void server_exit(void){
        printk("good bye\n");
}

module_init(server_init);
module_exit(server_exit);

MODULE_LICENSE("GPL");

3.client模块

/*client.c*/
#include
#include
#include
#include

#include
#include

int myclient(void){
        struct socket *sock;
        struct sockaddr_in s_addr;
        unsigned short portnum=0x8888;
        int ret=0;

        memset(&s_addr,0,sizeof(s_addr));
        s_addr.sin_family=AF_INET;
        s_addr.sin_port=htons(portnum);
     
        s_addr.sin_addr.s_addr=in_aton("192.168.209.134"); /*server ip is 192.168.209.134*/
        sock=(struct socket *)kmalloc(sizeof(struct socket),GFP_KERNEL);

        /*create a socket*/
        ret=sock_create_kern(AF_INET, SOCK_STREAM,0,&sock);
        if(ret<0){
                printk("client:socket create error!\n");
                return ret;
        }
        printk("client: socket create ok!\n");

        /*connect server*/
        ret=sock->ops->connect(sock,(struct sockaddr *)&s_addr, sizeof(s_addr),0);
        if(ret!=0){
                printk("client:connect error!\n");
                return ret;
        }
        printk("client:connect ok!\n");

        /*kmalloc sendbuf*/
        char *sendbuf=NULL;
        sendbuf=kmalloc(1024,GFP_KERNEL);
        if(sendbuf==NULL){
                printk("client: sendbuf kmalloc error!\n");
                return -1;
        }
        memset(sendbuf,1,1024);        
        
	struct kvec vec;
        struct msghdr msg;

        vec.iov_base=sendbuf;
        vec.iov_len=1024;

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

        ret=kernel_sendmsg(sock,&msg,&vec,1,1024); /*send message */
        if(ret<0){
                printk("client: kernel_sendmsg error!\n");
                return ret;
        }else if(ret!=1024){
                printk("client: ret!=1024");
        }
        printk("client:send ok!\n");

        return ret;
}

static int client_init(void){
        printk("client:init\n");
        return (myclient());
}

static void client_exit(void){
        printk("client exit!\n");
}

module_init(client_init);
module_exit(client_exit);
MODULE_LICENSE("GPL");

编译上面两个模块，首先在server主机上加载server模块，然后在client主机上加载client模块。使用dmesg查看输出信息。