6.3.11.11. socket

socket函数的原型为 int socket(int domain, int type, int protocol);

其中domain即协议域,又称为协议族(family)。常用的协议族有AF_INET、AF_INET6、AF_LOCAL(或称AF_UNIX,Unix域socket)、AF_ROUTE等等。协议族决定了socket的地址类型,在通信中必须采用对应的地址,如AF_INET决定了要用IPv4地址(32位的)与端口号(16位的)的组合、AF_UNIX要使用一个绝对路径名作为地址。

支持的所有协议定义在 /include/linux/socket.h 中,具体内容如下:

/* Supported address families. */
#define AF_UNSPEC   0
#define AF_UNIX     1   /* Unix domain sockets      */
#define AF_LOCAL    1   /* POSIX name for AF_UNIX   */
#define AF_INET     2   /* Internet IP Protocol     */
#define AF_AX25     3   /* Amateur Radio AX.25      */
#define AF_IPX      4   /* Novell IPX           */
#define AF_APPLETALK    5   /* AppleTalk DDP        */
#define AF_NETROM   6   /* Amateur Radio NET/ROM    */
#define AF_BRIDGE   7   /* Multiprotocol bridge     */
#define AF_ATMPVC   8   /* ATM PVCs         */
#define AF_X25      9   /* Reserved for X.25 project    */
#define AF_INET6    10  /* IP version 6         */
#define AF_ROSE     11  /* Amateur Radio X.25 PLP   */
#define AF_DECnet   12  /* Reserved for DECnet project  */
#define AF_NETBEUI  13  /* Reserved for 802.2LLC project*/
#define AF_SECURITY 14  /* Security callback pseudo AF */
#define AF_KEY      15      /* PF_KEY key management API */
#define AF_NETLINK  16
#define AF_ROUTE    AF_NETLINK /* Alias to emulate 4.4BSD */
#define AF_PACKET   17  /* Packet family        */
#define AF_ASH      18  /* Ash              */
#define AF_ECONET   19  /* Acorn Econet         */
#define AF_ATMSVC   20  /* ATM SVCs         */
#define AF_RDS      21  /* RDS sockets          */
#define AF_SNA      22  /* Linux SNA Project (nutters!) */
#define AF_IRDA     23  /* IRDA sockets         */
#define AF_PPPOX    24  /* PPPoX sockets        */
#define AF_WANPIPE  25  /* Wanpipe API Sockets */
#define AF_LLC      26  /* Linux LLC            */
#define AF_IB       27  /* Native InfiniBand address    */
#define AF_MPLS     28  /* MPLS */
#define AF_CAN      29  /* Controller Area Network      */
#define AF_TIPC     30  /* TIPC sockets         */
#define AF_BLUETOOTH    31  /* Bluetooth sockets        */
#define AF_IUCV     32  /* IUCV sockets         */
#define AF_RXRPC    33  /* RxRPC sockets        */
#define AF_ISDN     34  /* mISDN sockets        */
#define AF_PHONET   35  /* Phonet sockets       */
#define AF_IEEE802154   36  /* IEEE802154 sockets       */
#define AF_CAIF     37  /* CAIF sockets         */
#define AF_ALG      38  /* Algorithm sockets        */
#define AF_NFC      39  /* NFC sockets          */
#define AF_VSOCK    40  /* vSockets         */
#define AF_KCM      41  /* Kernel Connection Multiplexor*/
#define AF_QIPCRTR  42  /* Qualcomm IPC Router          */
#define AF_SMC      43  /* smc sockets: reserve number for
                 * PF_SMC protocol family that
                 * reuses AF_INET address family
                 */
#define AF_XDP      44  /* XDP sockets          */

#define AF_MAX      45  /* For now.. */

type指定socket类型,常用的socket类型为:

enum sock_type {
    SOCK_STREAM = 1, // 字节流套接字
    SOCK_DGRAM  = 2, // 数据报文套接字
    SOCK_RAW    = 3, // 原始套接字
    SOCK_RDM    = 4,
    SOCK_SEQPACKET  = 5, // 有序分组套接字
    SOCK_DCCP   = 6,
    SOCK_PACKET = 10,
};

protocol指协议,常用的协议类型为:

/* Standard well-defined IP protocols.  */
enum {
  IPPROTO_IP = 0,       /* Dummy protocol for TCP       */
#define IPPROTO_IP      IPPROTO_IP
  IPPROTO_ICMP = 1,     /* Internet Control Message Protocol    */
#define IPPROTO_ICMP        IPPROTO_ICMP
  IPPROTO_IGMP = 2,     /* Internet Group Management Protocol   */
#define IPPROTO_IGMP        IPPROTO_IGMP
  IPPROTO_IPIP = 4,     /* IPIP tunnels (older KA9Q tunnels use 94) */
#define IPPROTO_IPIP        IPPROTO_IPIP
  IPPROTO_TCP = 6,      /* Transmission Control Protocol    */
#define IPPROTO_TCP     IPPROTO_TCP
  IPPROTO_EGP = 8,      /* Exterior Gateway Protocol        */
#define IPPROTO_EGP     IPPROTO_EGP
  IPPROTO_PUP = 12,     /* PUP protocol             */
#define IPPROTO_PUP     IPPROTO_PUP
  IPPROTO_UDP = 17,     /* User Datagram Protocol       */
#define IPPROTO_UDP     IPPROTO_UDP
  IPPROTO_IDP = 22,     /* XNS IDP protocol         */
#define IPPROTO_IDP     IPPROTO_IDP
  IPPROTO_TP = 29,      /* SO Transport Protocol Class 4    */
#define IPPROTO_TP      IPPROTO_TP
  IPPROTO_DCCP = 33,        /* Datagram Congestion Control Protocol */
#define IPPROTO_DCCP        IPPROTO_DCCP
  IPPROTO_IPV6 = 41,        /* IPv6-in-IPv4 tunnelling      */
#define IPPROTO_IPV6        IPPROTO_IPV6
  IPPROTO_RSVP = 46,        /* RSVP Protocol            */
#define IPPROTO_RSVP        IPPROTO_RSVP
  IPPROTO_GRE = 47,     /* Cisco GRE tunnels (rfc 1701,1702)    */
#define IPPROTO_GRE     IPPROTO_GRE
  IPPROTO_ESP = 50,     /* Encapsulation Security Payload protocol */
#define IPPROTO_ESP     IPPROTO_ESP
  IPPROTO_AH = 51,      /* Authentication Header protocol   */
#define IPPROTO_AH      IPPROTO_AH
  IPPROTO_MTP = 92,     /* Multicast Transport Protocol     */
#define IPPROTO_MTP     IPPROTO_MTP
  IPPROTO_BEETPH = 94,      /* IP option pseudo header for BEET */
#define IPPROTO_BEETPH      IPPROTO_BEETPH
  IPPROTO_ENCAP = 98,       /* Encapsulation Header         */
#define IPPROTO_ENCAP       IPPROTO_ENCAP
  IPPROTO_PIM = 103,        /* Protocol Independent Multicast   */
#define IPPROTO_PIM     IPPROTO_PIM
  IPPROTO_COMP = 108,       /* Compression Header Protocol      */
#define IPPROTO_COMP        IPPROTO_COMP
  IPPROTO_SCTP = 132,       /* Stream Control Transport Protocol    */
#define IPPROTO_SCTP        IPPROTO_SCTP
  IPPROTO_UDPLITE = 136,    /* UDP-Lite (RFC 3828)          */
#define IPPROTO_UDPLITE     IPPROTO_UDPLITE
  IPPROTO_MPLS = 137,       /* MPLS in IP (RFC 4023)        */
#define IPPROTO_MPLS        IPPROTO_MPLS
  IPPROTO_ETHERNET = 143,   /* Ethernet-within-IPv6 Encapsulation   */
#define IPPROTO_ETHERNET    IPPROTO_ETHERNET
  IPPROTO_RAW = 255,        /* Raw IP packets           */
#define IPPROTO_RAW     IPPROTO_RAW
  IPPROTO_MPTCP = 262,      /* Multipath TCP connection     */
#define IPPROTO_MPTCP       IPPROTO_MPTCP
  IPPROTO_MAX
};