回环网卡(loop)
回环网卡的Tx通道和Rx通道是直连的，所以数据直接发送到接收端口。
编写回环网卡驱动
回环网卡驱动在/driver/net/loopback.c
#include <linux/kernel.h> #include <linux/jiffies.h> #include <linux/module.h> #include <linux/interrupt.h> #include <linux/fs.h> #include <linux/types.h> #include <linux/string.h> #include <linux/socket.h> #include <linux/errno.h> #include <linux/fcntl.h> #include <linux/in.h> #include <linux/init.h> #include <asm/system.h> #include <asm/uaccess.h> #include <asm/io.h> #include <linux/inet.h> #include <linux/netdevice.h> #include <linux/etherdevice.h> #include <linux/skbuff.h> #include <linux/ethtool.h> #include <net/sock.h> #include <net/checksum.h> #include <linux/if_ether.h> #include <linux/if_arp.h> #include <linux/ip.h> #include <linux/tcp.h> #include <linux/percpu.h> #include <net/net_namespace.h> unsigned long bytes = 0; //发送数据长度 unsigned long packets = 0; //发送报文个数 //网卡发送数据 int loopback_xmit(struct sk_buff *skb, struct net_device *dev){ //设置网络协议 skb->protocol = eth_type_trans(skb, dev); //设置发送信息 bytes += skb->len; //发送数据长度 packets++; //发送报文个数 //发送到协议栈 netif_rx(skb); return 0; } //网卡发送状态 static struct net_device_stats *loopback_get_stats(struct net_device *dev){ //设置发送状态 struct net_device_stats *stats = &dev->stats; stats->tx_bytes = bytes; stats->rx_bytes = bytes; stats->tx_packets = packets; stats->rx_packets = packets; return stats; } //网卡操作方法 struct net_device_ops loopback_ops = { .ndo_start_xmit = loopback_xmit, //发送数据 .ndo_get_stats = loopback_get_stats //发送状态 }; //设置网卡结构 static void loopback_setup(struct net_device *dev){ dev->mtu = (16 * 1024) + 20 + 20 + 12; //报文最大长度 dev->hard_header_len = ETH_HLEN; //14 dev->addr_len = ETH_ALEN; //6 dev->tx_queue_len = 0; dev->type = ARPHRD_LOOPBACK; //0x0001 dev->flags = IFF_LOOPBACK; //设置回环标志 dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; dev->features = NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO | NETIF_F_NO_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX | NETIF_F_NETNS_LOCAL; dev->header_ops = ð_header_ops; //设置以太头部 dev->netdev_ops = &loopback_ops; //设置操作方法 } /* Setup and register the loopback device. */ static __net_init int loopback_net_init(struct net *net){ //分配网卡结构 struct net_device *dev; dev = alloc_netdev(0, "lo", loopback_setup); //注册网卡结构 register_netdev(dev); //设置网卡结构 net->loopback_dev = dev; return 0; } static __net_exit void loopback_net_exit(struct net *net){ //注销网卡结构 struct net_device *dev; dev = net->loopback_dev; unregister_netdev(dev); } /* Registered in net/core/dev.c */ struct pernet_operations __net_initdata loopback_net_ops = { .init = loopback_net_init, .exit = loopback_net_exit, };