内核态socket编程

 

内核态的socket编程

分类： 嵌入式开发 2013-06-17 15:32   794人阅读   评论(0)   收藏   举报

记不清从哪个kernel版本开始，内核态就不能直接使用系统调用了。当然，socket的系统调用也不能用了。不过好在kernel提供了一组内核态的socket API。在net/socket.c文件中，可以看到这么几个导出符号：

 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);

基本上，在用户态的socket的API，在内核态都有对应的API。

下面是一个项目中的代码，socket操作我加了注视。不用去关心代码功能，只要看一下socket部分的操作即可，非常简单。

 #include
 #include
 #include

 struct fsg_common{
 ....
         struct socket *encrypt_sock;
         struct msghdr encrypt_msg;
         struct sockaddr_in encrypt_servaddr;
         struct data_pkt *encrypt_pkt;
 }

 static int encrypt_socket_init(struct fsg_common *common)
 {
     struct socket *sock;
     int ret;
     char *dst_addr = "111.111.111.111";
     /* init servaddr */
     memset(&common->encrypt_servaddr, 0, sizeof(common->encrypt_servaddr));
     common->encrypt_servaddr.sin_family = AF_INET;
     common->encrypt_servaddr.sin_port = htons(9999);

     //kernel态的IP地址转换函数，有两个函数in4_pton和in6_pton，分别用于IPv4和IPv6
     in4_pton(dst_addr, strlen(dst_addr), (u8*)&common->encrypt_servaddr.sin_addr, '\0', NULL);

     //内核态udp通信地址使用struct msghdr封装
     common->encrypt_msg.msg_name = &common->encrypt_servaddr;
     common->encrypt_msg.msg_namelen = sizeof(common->encrypt_servaddr);

     //创建套接字，类似socket()函数，返回的sock指针就是后面数据传递用的套接字了
     ret = sock_create_kern(AF_INET, SOCK_DGRAM, IPPROTO_UDP, &sock);
     if (ret < 0 || NULL == sock) {
         ERROR(common, "init encrypt board socket fail\n");
         return ret;
     }
     common->encrypt_sock = sock;

     common->encrypt_pkt = kmalloc(sizeof(struct data_pkt), GFP_KERNEL);
     if (NULL == common->encrypt_pkt)
         return -1;

     return 0;
 }

 static void encrypt_socket_close(struct fsg_common *common)
 {
     //关闭套接字，类似用户态的close()函数
     sock_release(common->encrypt_sock);
     common->encrypt_sock = NULL;
 }

 static int encrypt_data(struct fsg_common *common, u8* data, unsigned int size, loff_t offset)
 {
     struct socket *sock = common->encrypt_sock;
     struct data_pkt *pkt = common->encrypt_pkt;
     struct sockaddr *pservaddr = (struct sockaddr *)&common->encrypt_servaddr;
     int servlen = sizeof(common->encrypt_servaddr);

     if (unlikely(NULL == sock || NULL == pkt || NULL == pservaddr))
         return -1;

     memset(pkt, 0, sizeof(struct data_pkt));
     unsigned int copied_size = 0;
     struct kvec vec;
     struct msghdr msg;
     memset(&msg, 0, sizeof(msg));

     while (copied_size < size) {
         pkt->res=0xffffffff;
         pkt->file_offset = offset;
         memcpy(pkt->data, data + copied_size, SECTOR_SIZE);

         //配置udp发送数据地址及长度
         vec.iov_base = (void *)pkt;
         vec.iov_len = sizeof(struct data_pkt);
         ret = kernel_sendmsg(sock, &common->encrypt_msg, &vec, 1, sizeof(struct data_pkt));
         printk("send data(return :%d):\n", ret);

         //接收udp报文
         ret = kernel_recvmsg(sock, &msg, &vec, 1, sizeof(struct data_pkt), 0);
         printk("recv data(return :%d):\n", ret);
         memcpy(data+copied_size, pkt->data, 512);
         copied_size += 512;
     }

     return 0;
 }