9.14 socket ¶

#define AF_UNIX       3
#define SOCK_DGRAM    0b000000000000000001
#define SOCK_RAW      0b000000000000000010
#define SOCK_STREAM   0b000000000000000100
#define SOCK_NONBLOCK 0b010000000000000000
#define SOCK_CLOEXEC  0b100000000000000000

int socket(int domain, int type);

This syscall for creating sockets, the passed fields can be used for selecting the type of socket to create. The available sockets type are:

• AF_INET: Basically IPv4 socket.

  The address of a INET domain socket takes the shape of

  struct sockaddr_in {
     uint32_t sin_family;
     uint16_t sin_port;
     char     sin_addr[4];
     uint8_t  pad[8];
  };
  

  type can be one of SOCK_DGRAM or SOCK_STREAM. SOCK_DGRAM will be translated to TCP, while SOCK_STREAM will be translated to UDP.

• AF_INET6: Basically IPv6 socket.

  The address of a INET domain socket takes the shape of

  struct sockaddr_in6 {
     uint32_t sin6_family;
     uint16_t sin6_port;
     uint32_t sin6_flowinfo;
     char     sin6_addr[16];
     uint32_t sin6_scope_id;
  };
  

  type can be one of SOCK_DGRAM or SOCK_STREAM. SOCK_DGRAM will be translated to TCP, while SOCK_STREAM will be translated to UDP.

• AF_UNIX: UNIX domain socket for local communication, this sockets can be unnamed or bound to filesystem paths.

  The address of a UNIX domain socket takes the shape of

  struct sockaddr_un {
     uint32_t sun_family; // AF_UNIX.
     char path[];         // Must be null terminated.
  };
  

type can be one of:

• SOCK_DGRAM: Unreliable, connection-less, datagram-based interface. When used with INET protocols, it will correspond to UDP. When connected, these sockets will just cache the address for further reception / sending.
• SOCK_STREAM: Reliable, connection-based stream-based interface. Connection, accepting, and listening will be necessary for a proper handshake.
• SOCK_RAW: Raw communication directly with the domain layer. When using these, no TCP or UDP will be done whatsoever, and the user will be free to implement their own protocol on top, or none at all and just use the domain datagram transport. Not supported for some protocols, like UNIX domain sockets.

Any socket type may have type be OR’ed with SOCK_NONBLOCK or SOCK_CLOEXEC for setting the created socket nonblock or cloese on exec respectively.

The syscall returns the resulting FD or -1 on failure, with the following errno:

• EINVAL: Invalid combination of flags.
• EMFILE: No available file descriptor slots.