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2025/12/23 6:57:14
第一部分：Socket API的通用性架构
它不仅封装了TCP/IP协议，还通过统一的接口支持了各种通信协议和设备。
1.1 Socket家族的树形结构
Linux Socket协议族全景图 ├── 标准网络协议族 │ ├── AF_INET (IPv4协议) │ ├── AF_INET6 (IPv6协议) │ ├── AF_UNIX/AF_LOCAL (本地进程通信) │ └── AF_PACKET (原始数据包) ├── 无线通信协议族 │ ├── AF_BLUETOOTH (蓝牙协议) │ │ ├── BTPROTO_HCI (主机控制器接口) │ │ ├── BTPROTO_SCO (同步面向连接) │ │ ├── BTPROTO_L2CAP (逻辑链路控制与适配协议) │ │ └── BTPROTO_RFCOMM (串口仿真) │ ├── AF_IEEE802154 (低功耗无线个域网) │ └── AF_NFC (近场通信) ├── 工业控制协议族 │ ├── AF_CAN (控制器局域网) │ │ ├── RAW_CAN (原始CAN帧) │ │ ├── BCM (广播管理器) │ │ └── ISO TP (ISO 15765-2传输协议) │ └── AF_CANFD (CAN FD扩展) ├── 其他特殊协议族 │ ├── AF_NETLINK (内核-用户空间通信) │ ├── AF_ALG (内核加密API) │ ├── AF_VSOCK (虚拟机通信) │ ├── AF_XDP (eXpress Data Path) │ └── AF_KCM (内核连接复用器) └── 已废弃/遗留协议族 ├── AF_IPX (Novell IPX) ├── AF_AX25 (业余无线电) └── AF_APPLETALK (AppleTalk)
1.2 Socket通用API设计
// net/socket.c - 统一的socket系统调用 SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol) { int retval; struct socket *sock; int flags; // 检查参数有效性 if (family < 0 || family >= NPROTO) return -EAFNOSUPPORT; // 分配和初始化socket结构 retval = sock_create(family, type, protocol, &sock); if (retval < 0) return retval; // 分配文件描述符 retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK)); if (retval < 0) { sock_release(sock); return retval; } return retval; } // 关键：所有socket共享的通用结构 struct socket { socket_state state; // 连接状态 short type; // SOCK_STREAM, SOCK_DGRAM等 unsigned long flags; // 标志位 // 核心：协议操作函数表 const struct proto_ops *ops; // 协议特定操作 struct fasync_struct *fasync_list; // 异步通知 struct file *file; // 关联的文件 struct sock *sk; // 协议私有数据 wait_queue_head_t wait; // 等待队列 short poll_mask; // poll掩码 };第二部分：蓝牙协议栈的Socket封装
2.1 蓝牙Socket架构
Linux蓝牙协议栈Socket集成 ├── 核心架构 (net/bluetooth/) │ ├── af_bluetooth.c - 蓝牙协议族注册 │ │ ├── 注册PF_BLUETOOTH协议族 │ │ ├── 实现proto_ops操作集 │ │ └── socket创建和绑定 │ └── 各协议层socket支持 │ ├── HCI层 (net/bluetooth/hci_sock.c) │ │ ├── BTPROTO_HCI socket类型 │ │ ├── 原始HCI命令/事件 │ │ └── 蓝牙设备控制 │ ├── L2CAP层 (net/bluetooth/l2cap_sock.c) │ │ ├── BTPROTO_L2CAP socket类型 │ │ ├── 面向连接的数据传输 │ │ └── 流控制和错误检测 │ ├── SCO层 (net/bluetooth/sco.c) │ │ ├── BTPROTO_SCO socket类型 │ │ └── 语音传输支持 │ └── RFCOMM层 (net/bluetooth/rfcomm/sock.c) │ ├── BTPROTO_RFCOMM socket类型 │ └── 串口仿真协议 ├── 用户空间API示例 │ ├── 创建蓝牙socket: socket(AF_BLUETOOTH, SOCK_RAW, BTPROTO_HCI) │ ├── L2CAP socket: socket(AF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP) │ └── RFCOMM socket: socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM) └── 工具链支持 ├── bluez蓝牙协议栈 ├── hcitool设备配置 └── bluetoothctl控制工具
蓝牙Socket的具体实现：
// net/bluetooth/af_bluetooth.c - 蓝牙协议族注册 static const struct net_proto_family bt_sock_family_ops = { .family = PF_BLUETOOTH, // 协议族号 .owner = THIS_MODULE, .create = bt_sock_create, // socket创建函数 }; // 蓝牙socket创建函数 static int bt_sock_create(struct net *net, struct socket *sock, int proto, int kern) { int err; // 根据协议类型选择不同的socket实现 switch (proto) { case BTPROTO_HCI: // HCI层socket err = hci_sock_create(net, sock, proto, kern); break; case BTPROTO_L2CAP: // L2CAP层socket err = l2cap_sock_create(net, sock, proto, kern); if (!err) bt_sock_link(&l2cap_sk_list, sock->sk); break; case BTPROTO_SCO: // SCO层socket err = sco_sock_create(net, sock, proto, kern); if (!err) bt_sock_link(&sco_sk_list, sock->sk); break; case BTPROTO_RFCOMM: // RFCOMM层socket err = rfcomm_sock_create(net, sock, proto, kern); if (!err) bt_sock_link(&rfcomm_sk_list, sock->sk); break; default: err = -EPROTONOSUPPORT; break; } return err; } // L2CAP socket操作集示例 static const struct proto_ops l2cap_sock_ops = { .family = PF_BLUETOOTH, .owner = THIS_MODULE, .release = l2cap_sock_release, .bind = l2cap_sock_bind, .connect = l2cap_sock_connect, .listen = l2cap_sock_listen, .accept = l2cap_sock_accept, .getname = l2cap_sock_getname, .sendmsg = l2cap_sock_sendmsg, .recvmsg = l2cap_sock_recvmsg, .poll = bt_sock_poll, .ioctl = bt_sock_ioctl, #ifdef CONFIG_COMPAT .compat_ioctl = bt_sock_compat_ioctl, #endif .mmap = sock_no_mmap, .socketpair = sock_no_socketpair, .shutdown = l2cap_sock_shutdown, .setsockopt = l2cap_sock_setsockopt, .getsockopt = l2cap_sock_getsockopt, };2.2 蓝牙Socket使用示例
// 用户空间使用蓝牙socket的示例 #include <sys/socket.h> #include <bluetooth/bluetooth.h> #include <bluetooth/hci.h> #include <bluetooth/hci_lib.h> // 示例1：扫描蓝牙设备 int scan_bluetooth_devices(void) { int dev_id = hci_get_route(NULL); // 获取第一个可用适配器 int sock = socket(AF_BLUETOOTH, SOCK_RAW, BTPROTO_HCI); struct sockaddr_hci addr = { .hci_family = AF_BLUETOOTH, .hci_dev = dev_id, }; // 绑定到HCI设备 bind(sock, (struct sockaddr *)&addr, sizeof(addr)); // 开始扫描 struct hci_filter flt; hci_filter_clear(&flt); hci_filter_set_ptype(HCI_EVENT_PKT, &flt); hci_filter_set_event(EVT_INQUIRY_RESULT, &flt); setsockopt(sock, SOL_HCI, HCI_FILTER, &flt, sizeof(flt)); // 发送查询命令 struct hci_request req; // ... 设置查询参数 ioctl(sock, HCISETSCAN, 1); // 开始扫描 // 接收扫描结果 unsigned char buf[HCI_MAX_EVENT_SIZE]; read(sock, buf, sizeof(buf)); close(sock); return 0; } // 示例2：L2CAP Socket通信 int l2cap_communication(void) { // 服务器端 int server_sock = socket(AF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP); struct sockaddr_l2 server_addr = { .l2_family = AF_BLUETOOTH, .l2_psm = htobs(0x1001), // L2CAP PSM .l2_bdaddr = *BDADDR_ANY, }; bind(server_sock, (struct sockaddr *)&server_addr, sizeof(server_addr)); listen(server_sock, 5); // 客户端 int client_sock = socket(AF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP); struct sockaddr_l2 client_addr = { .l2_family = AF_BLUETOOTH, .l2_psm = htobs(0x1001), .l2_bdaddr = {{0x00, 0x1A, 0x7D, 0xDA, 0x71, 0x13}}, // 目标地址 }; connect(client_sock, (struct sockaddr *)&client_addr, sizeof(client_addr)); // 数据传输 char buffer[1024]; send(client_sock, "Hello Bluetooth", 15, 0); recv(server_sock, buffer, sizeof(buffer), 0); close(server_sock); close(client_sock); return 0; }第三部分：CAN总线Socket封装
3.1 CAN协议栈Socket架构
Linux CAN协议栈Socket集成 ├── 核心架构 (net/can/) │ ├── af_can.c - CAN协议族注册 │ │ ├── 注册PF_CAN协议族 │ │ ├── 实现协议操作函数 │ │ └── 核心数据结构管理 │ ├── 协议模块 │ │ ├── raw.c - 原始CAN socket (SOCK_RAW) │ │ │ ├── 直接访问CAN控制器 │ │ │ ├── 过滤器和错误处理 │ │ │ └── 时间戳支持 │ │ ├── bcm.c - 广播管理器socket │ │ │ ├── 周期消息发送 │ │ │ ├── 变化检测 │ │ │ └── CAN帧序列 │ │ └── isotp.c - ISO-TP传输协议 │ │ ├── 大数据块分段传输 │ │ ├── 流控制和错误处理 │ │ └── 诊断协议支持 │ └── 设备接口层 │ ├── can-dev.c - 通用CAN设备框架 │ ├── 各种CAN控制器驱动 │ └── 虚拟CAN设备支持 ├── 数据结构 │ ├── struct can_frame - CAN数据帧 │ ├── struct can_filter - 过滤器结构 │ └── struct can_bcm_msg - BCM消息 └── Socket选项和IOCTL ├── CAN_RAW_FILTER - 设置过滤器 ├── CAN_RAW_ERR_FILTER - 错误过滤器 ├── CAN_RAW_LOOPBACK - 回环模式 └── CAN_RAW_RECV_OWN_MSGS - 接收自己发送的帧
CAN Socket的具体实现：
// net/can/af_can.c - CAN协议族注册 static const struct net_proto_family can_family_ops = { .family = PF_CAN, .create = can_create, .owner = THIS_MODULE, }; // CAN socket创建 static int can_create(struct net *net, struct socket *sock, int protocol, int kern) { struct sock *sk; int rc = 0; // 检查协议类型 if (protocol < 0 || protocol >= CAN_NPROTO) return -EINVAL; // 根据协议类型创建不同的socket switch (protocol) { case CAN_RAW: rc = raw_init(sock); // 原始CAN socket break; case CAN_BCM: rc = bcm_init(sock); // 广播管理器socket break; case CAN_ISOTP: rc = isotp_init(sock); // ISO-TP socket break; default: rc = -EPROTONOSUPPORT; break; } if (!rc) { sk = sock->sk; sk->sk_family = PF_CAN; sk->sk_protocol = protocol; } return rc; } // CAN核心数据结构 struct can_frame { canid_t can_id; // 32位 CAN ID + EFF/RTR/ERR标志 __u8 can_dlc; // 数据长度码 __u8 __pad; // 填充 __u8 __res0; // 保留 __u8 __res1; // 保留 __u8 data[CAN_MAX_DLEN] __attribute__((aligned(8))); // 数据 }; // CAN过滤器结构 struct can_filter { canid_t can_id; // 匹配的CAN ID canid_t can_mask; // 掩码（0=不关心） }; // 原始CAN socket操作集 static const struct proto_ops raw_ops = { .family = PF_CAN, .owner = THIS_MODULE, .release = raw_release, .bind = raw_bind, .connect = sock_no_connect, .socketpair = sock_no_socketpair, .accept = sock_no_accept, .getname = raw_getname, .poll = datagram_poll, .ioctl = raw_ioctl, .gettstamp = sock_gettstamp, .listen = sock_no_listen, .shutdown = sock_no_shutdown, .setsockopt = raw_setsockopt, .getsockopt = raw_getsockopt, .sendmsg = raw_sendmsg, .recvmsg = raw_recvmsg, .mmap = sock_no_mmap, .sendpage = sock_no_sendpage, };3.2 CAN Socket使用示例
// 用户空间使用CAN socket的示例 #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <net/if.h> #include <sys/ioctl.h> #include <sys/socket.h> #include <linux/can.h> #include <linux/can/raw.h> // 示例1：原始CAN Socket读写 int raw_can_example(void) { int s; struct sockaddr_can addr; struct ifreq ifr; struct can_frame frame; // 创建CAN原始socket s = socket(PF_CAN, SOCK_RAW, CAN_RAW); if (s < 0) { perror("Socket creation failed"); return -1; } // 绑定到具体CAN接口 strcpy(ifr.ifr_name, "can0"); ioctl(s, SIOCGIFINDEX, &ifr); addr.can_family = AF_CAN; addr.can_ifindex = ifr.ifr_ifindex; if (bind(s, (struct sockaddr *)&addr, sizeof(addr)) < 0) { perror("Bind failed"); close(s); return -1; } // 设置过滤器（只接收ID 0x123-0x125） struct can_filter rfilter[3]; rfilter[0].can_id = 0x123; rfilter[0].can_mask = CAN_SFF_MASK; // 标准帧格式 rfilter[1].can_id = 0x124; rfilter[1].can_mask = CAN_SFF_MASK; rfilter[2].can_id = 0x125; rfilter[2].can_mask = CAN_SFF_MASK; setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter)); // 发送CAN帧 frame.can_id = 0x123 | CAN_EFF_FLAG; // 扩展帧 frame.can_dlc = 8; memcpy(frame.data, "HelloCAN!", 8); if (write(s, &frame, sizeof(frame)) != sizeof(frame)) { perror("Write failed"); } // 接收CAN帧 int nbytes = read(s, &frame, sizeof(frame)); if (nbytes > 0) { printf("Received CAN frame ID: 0x%X DLC: %d Data: ", frame.can_id & CAN_EFF_MASK, frame.can_dlc); for (int i = 0; i < frame.can_dlc; i++) { printf("%02X ", frame.data[i]); } printf("\n"); } close(s); return 0; } // 示例2：CAN广播管理器（BCM）示例 int bcm_example(void) { int s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM); struct sockaddr_can addr; struct ifreq ifr; strcpy(ifr.ifr_name, "can0"); ioctl(s, SIOCGIFINDEX, &ifr); addr.can_family = AF_CAN; addr.can_ifindex = ifr.ifr_ifindex; connect(s, (struct sockaddr *)&addr, sizeof(addr)); // 设置周期性发送消息 struct bcm_msg_head msg_head; struct can_frame frame; msg_head.opcode = TX_SETUP; msg_head.flags = SETTIMER | STARTTIMER; msg_head.count = 0; // 无限发送 msg_head.ival1.tv_sec = 1; // 每1秒 msg_head.ival1.tv_usec = 0; msg_head.nframes = 1; frame.can_id = 0x100; frame.can_dlc = 2; frame.data[0] = 0xAA; frame.data[1] = 0x55; // 发送BCM消息 struct iovec iov[2]; iov[0].iov_base = &msg_head; iov[0].iov_len = sizeof(msg_head); iov[1].iov_base = &frame; iov[1].iov_len = sizeof(frame); writev(s, iov, 2); close(s); return 0; } // 示例3：ISO-TP（诊断协议）示例 int isotp_example(void) { int s = socket(PF_CAN, SOCK_DGRAM, CAN_ISOTP); struct sockaddr_can addr; struct ifreq ifr; strcpy(ifr.ifr_name, "can0"); ioctl(s, SIOCGIFINDEX, &ifr); addr.can_family = AF_CAN; addr.can_ifindex = ifr.ifr_ifindex; addr.can_addr.tp.tx_id = 0x7E0; // 发送ID addr.can_addr.tp.rx_id = 0x7E8; // 接收ID bind(s, (struct sockaddr *)&addr, sizeof(addr)); // ISO-TP可以传输超过8字节的数据 unsigned char isotp_data[4096]; struct iovec iov = { .iov_base = isotp_data, .iov_len = 100 }; // 发送大数据块（会自动分段） sendmsg(s, &(struct msghdr){ .msg_iov = &iov, .msg_iovlen = 1, }, 0); // 接收数据 recv(s, isotp_data, sizeof(isotp_data), 0); close(s); return 0; }第四部分：其他特殊协议Socket
4.1 Netlink Socket（内核-用户空间通信）
// net/netlink/af_netlink.c /* Netlink Socket实现 */ static const struct net_proto_family netlink_family_ops = { .family = PF_NETLINK, .create = netlink_create, .owner = THIS_MODULE, }; // Netlink消息结构 struct nlmsghdr { __u32 nlmsg_len; // 消息长度（包括头部） __u16 nlmsg_type; // 消息类型 __u16 nlmsg_flags; // 标志位 __u32 nlmsg_seq; // 序列号 __u32 nlmsg_pid; // 发送进程PID }; // Netlink使用示例 int netlink_example(void) { int sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE); struct sockaddr_nl src_addr = { .nl_family = AF_NETLINK, .nl_pid = getpid(), // 当前进程PID .nl_groups = 0, // 不加入多播组 }; bind(sock_fd, (struct sockaddr *)&src_addr, sizeof(src_addr)); // 构建Netlink消息（查询网络接口） struct { struct nlmsghdr nlh; struct ifinfomsg ifm; } req; memset(&req, 0, sizeof(req)); req.nlh.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg)); req.nlh.nlmsg_type = RTM_GETLINK; req.nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP; req.nlh.nlmsg_seq = 1; req.nlh.nlmsg_pid = getpid(); req.ifm.ifi_family = AF_UNSPEC; // 发送请求 send(sock_fd, &req, req.nlh.nlmsg_len, 0); // 接收响应 char buf[8192]; struct nlmsghdr *nlh = (struct nlmsghdr *)buf; recv(sock_fd, buf, sizeof(buf), 0); // 解析响应 for (; NLMSG_OK(nlh, recv_len); nlh = NLMSG_NEXT(nlh, recv_len)) { if (nlh->nlmsg_type == NLMSG_DONE) break; struct ifinfomsg *ifinfo = NLMSG_DATA(nlh); printf("Interface index: %d\n", ifinfo->ifi_index); } close(sock_fd); return 0; }4.2 VSOCK Socket（虚拟机通信）
// net/vmw_vsock/af_vsock.c /* VSOCK协议族实现 */ static const struct net_proto_family vsock_family_ops = { .family = AF_VSOCK, .create = vsock_create, .owner = THIS_MODULE, }; // VSOCK地址结构 struct sockaddr_vm { sa_family_t svm_family; // AF_VSOCK unsigned short svm_reserved1; unsigned int svm_port; // 端口号 unsigned int svm_cid; // 上下文ID unsigned char svm_zero[sizeof(struct sockaddr) - sizeof(sa_family_t) - sizeof(unsigned short) - sizeof(unsigned int) - sizeof(unsigned int)]; }; // VSOCK使用示例 int vsock_example(void) { // 主机端（CID=2） int server_fd = socket(AF_VSOCK, SOCK_STREAM, 0); struct sockaddr_vm server_addr = { .svm_family = AF_VSOCK, .svm_cid = VMADDR_CID_ANY, // 监听所有CID .svm_port = 1234, }; bind(server_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)); listen(server_fd, 5); // 虚拟机内（CID=3） int client_fd = socket(AF_VSOCK, SOCK_STREAM, 0); struct sockaddr_vm client_addr = { .svm_family = AF_VSOCK, .svm_cid = VMADDR_CID_HOST, // 主机CID .svm_port = 1234, }; connect(client_fd, (struct sockaddr *)&client_addr, sizeof(client_addr)); // 数据传输（虚拟机<->主机） char buffer[1024]; send(client_fd, "Hello from VM", 13, 0); recv(server_fd, buffer, sizeof(buffer), 0); close(client_fd); close(server_fd); return 0; }4.3 ALG Socket（内核加密API）
// crypto/af_alg.c /* 内核加密API Socket */ static const struct net_proto_family alg_family_ops = { .family = PF_ALG, .create = alg_create, .owner = THIS_MODULE, }; // ALG Socket使用示例 int alg_example(void) { // 创建加密socket int sock_fd = socket(AF_ALG, SOCK_SEQPACKET, 0); struct sockaddr_alg sa = { .salg_family = AF_ALG, .salg_type = "skcipher", // 对称加密 .salg_name = "cbc(aes)", // AES-CBC算法 }; bind(sock_fd, (struct sockaddr *)&sa, sizeof(sa)); // 设置密钥 unsigned char key[32] = { /* 256位密钥 */ }; setsockopt(sock_fd, SOL_ALG, ALG_SET_KEY, key, sizeof(key)); // 创建加密操作的文件描述符 int op_fd = accept(sock_fd, NULL, NULL); // 加密数据 unsigned char plaintext[64] = "Data to encrypt"; unsigned char ciphertext[64]; // 设置IV（初始化向量） unsigned char iv[16] = {0}; setsockopt(op_fd, SOL_ALG, ALG_SET_IV, iv, sizeof(iv)); // 执行加密 write(op_fd, plaintext, sizeof(plaintext)); read(op_fd, ciphertext, sizeof(ciphertext)); close(op_fd); close(sock_fd); return 0; }第五部分：Socket API设计的精妙之处
5.1 统一的接口设计模式
/* Socket API的通用模式 */ struct socket_api_pattern { // 1. 地址结构统一 struct sockaddr { sa_family_t sa_family; // 协议族标识符 char sa_data[14]; // 协议特定地址 }; // 2. 统一的系统调用 int socket(int domain, int type, int protocol); int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen); int listen(int sockfd, int backlog); int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen); int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen); ssize_t send(int sockfd, const void *buf, size_t len, int flags); ssize_t recv(int sockfd, void *buf, size_t len, int flags); int getsockopt(int sockfd, int level, int optname, void *optval, socklen_t *optlen); int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t optlen); int close(int fd); // 3. 协议特定的操作通过proto_ops抽象 struct proto_ops { int (*bind)(struct socket *sock, struct sockaddr *myaddr, int sockaddr_len); int (*connect)(struct socket *sock, struct sockaddr *vaddr, int sockaddr_len, int flags); int (*socketpair)(struct socket *sock1, struct socket *sock2); int (*accept)(struct socket *sock, struct socket *newsock, int flags); int (*getname)(struct socket *sock, struct sockaddr *addr, int peer); unsigned int (*poll)(struct file *file, struct socket *sock, struct poll_table_struct *wait); int (*ioctl)(struct socket *sock, unsigned int cmd, unsigned long arg); int (*listen)(struct socket *sock, int len); int (*shutdown)(struct socket *sock, int flags); int (*setsockopt)(struct socket *sock, int level, int optname, char __user *optval, unsigned int optlen); int (*getsockopt)(struct socket *sock, int level, int optname, char __user *optval, int __user *optlen); int (*sendmsg)(struct socket *sock, struct msghdr *m, int total_len); int (*recvmsg)(struct socket *sock, struct msghdr *m, int total_len, int flags); int (*mmap)(struct file *file, struct socket *sock, struct vm_area_struct *vma); ssize_t (*sendpage)(struct socket *sock, struct page *page, int offset, size_t size, int flags); ssize_t (*splice_read)(struct socket *sock, loff_t *ppos, struct pipe_inode_info *pipe, size_t len, unsigned int flags); }; };5.2 文件描述符的魔力
/* * Socket设计最精妙之处：统一到文件描述符抽象 * * 所有socket都映射到一个文件描述符，这带来了： * 1. 统一的I/O操作（read/write/select/poll/epoll） * 2. 继承和复制语义（通过fork和exec） * 3. 资源管理一致性（close自动清理） * 4. 权限控制（通过文件权限位） */ // 内核中的socket文件操作 static const struct file_operations socket_file_ops = { .owner = THIS_MODULE, .llseek = no_llseek, .read_iter = sock_read_iter, // 支持readv/read .write_iter = sock_write_iter, // 支持writev/write .poll = sock_poll, // poll/epoll支持 .unlocked_ioctl = sock_ioctl, // ioctl支持 .mmap = sock_mmap, // mmap支持 .release = sock_close, // close时清理 .fasync = sock_fasync, // 异步通知 .sendpage = sock_sendpage, // sendfile零拷贝 .splice_write = generic_splice_sendpage, // splice支持 .splice_read = sock_splice_read, }; // 这使得以下代码对所有socket都有效 int handle_socket_io(int sock_fd) { fd_set read_fds; struct timeval tv; FD_ZERO(&read_fds); FD_SET(sock_fd, &read_fds); tv.tv_sec = 5; tv.tv_usec = 0; // select可以用于任何socket int ret = select(sock_fd + 1, &read_fds, NULL, NULL, &tv); if (ret > 0 && FD_ISSET(sock_fd, &read_fds)) { char buffer[1024]; // read可以用于任何socket ssize_t n = read(sock_fd, buffer, sizeof(buffer)); if (n > 0) { // 处理数据 } } return 0; }第六部分：现代扩展和未来趋势
6.1 XDP Socket（eBPF驱动的高速包处理）
// net/xdp/xsk.c /* XDP Socket实现 */ static const struct net_proto_family xsk_family_ops = { .family = AF_XDP, .create = xsk_create, .owner = THIS_MODULE, }; // XDP Socket使用示例 SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx) { int index = ctx->rx_queue_index; // 重定向到用户空间socket if (bpf_map_lookup_elem(&xsks_map, &index)) { return bpf_redirect_map(&xsks_map, index, 0); } return XDP_PASS; } // 用户空间XDP Socket使用 int xdp_socket_example(void) { // 创建XDP socket int sock_fd = socket(AF_XDP, SOCK_RAW, 0); // 绑定到特定队列 struct sockaddr_xdp sxdp = { .sxdp_family = AF_XDP, .sxdp_ifindex = if_nametoindex("eth0"), .sxdp_queue_id = 0, // RX队列0 }; bind(sock_fd, (struct sockaddr *)&sxdp, sizeof(sxdp)); // 设置环形缓冲区（零拷贝） struct xdp_mmap_offsets off; getsockopt(sock_fd, SOL_XDP, XDP_MMAP_OFFSETS, &off, sizeof(off)); void *rx_map = mmap(NULL, off.rx.desc + NUM_DESCS * sizeof(struct xdp_desc), PROT_READ | PROT_WRITE, MAP_SHARED, sock_fd, XDP_PGOFF_RX_RING); // 直接访问数据包（绕过内核协议栈） struct xdp_desc *rx_desc = rx_map + off.rx.desc; while (1) { // 检查是否有新数据包 if (rx_desc->addr) { void *packet_data = rx_map + rx_desc->addr; // 处理原始数据包，极低延迟 process_packet(packet_data, rx_desc->len); // 释放描述符 rx_desc->addr = 0; } } close(sock_fd); return 0; }6.2 KCM Socket（内核连接复用器）
// net/kcm/kcmsock.c /* KCM Socket实现 - 将多个socket复用为一个 */ static const struct net_proto_family kcm_family_ops = { .family = AF_KCM, .create = kcm_create, .owner = THIS_MODULE, }; // KCM使用示例：将多个TCP连接复用为一个socket int kcm_multiplex_example(void) { int kcm_fd = socket(AF_KCM, SOCK_DGRAM, 0); struct sockaddr_kcm skcm; // 创建KCM multiplexer memset(&skcm, 0, sizeof(skcm)); skcm.skcm_family = AF_KCM; skcm.skcm_ifindex = 0; // 自动分配 bind(kcm_fd, (struct sockaddr *)&skcm, sizeof(skcm)); // 添加TCP socket到KCM多路复用器 int tcp_fd = socket(AF_INET, SOCK_STREAM, 0); // ... 连接TCP服务器 // 将TCP socket附加到KCM struct kcm_attach attach_info = { .fd = tcp_fd, }; setsockopt(kcm_fd, SOL_KCM, KCM_ATTACH, &attach_info, sizeof(attach_info)); // 现在可以通过单个KCM socket读写所有附加的socket char buffer[1024]; // 从任何连接的socket接收数据 recv(kcm_fd, buffer, sizeof(buffer), 0); // 发送到所有连接的socket（或特定socket） send(kcm_fd, buffer, strlen(buffer), 0); close(kcm_fd); return 0; }Socket API确实是Linux网络子系统最成功的设计之一。它通过统一的接口抽象了各种底层通信协议，从传统的TCP/IP到蓝牙、CAN总线，再到现代的高速数据处理（XDP）和内核加密（ALG）。这种设计体现了UNIX哲学中"万物皆文件"的思想，将复杂的网络通信简化为文件描述符操作，极大地简化了应用程序的开发。
这种架构的美妙之处在于其可扩展性和一致性：
可扩展性：任何新的通信协议都可以通过实现proto_ops接口集成到socket框架中
一致性：所有socket都支持相同的I/O多路复用机制（select/poll/epoll）
安全性：通过文件权限和命名空间提供访问控制
性能：支持零拷贝、内存映射等高级优化
这正是为什么Linux能够支持从嵌入式设备到超级计算机的各种网络需求，从工业控制（CAN）到消费电子（蓝牙），从传统网络（TCP/IP）到现代云原生（XDP），所有这些都通过统一的socket API实现。