socket(7)

NAME

socket − Interprocess communications

DESCRIPTION

Sockets are communication endpoints that allow processes to communicate either locally or remotely. They are accessed by means of a set of system calls (see socket(2)).

The following ioctl() requests are defined in <sys/ioctl.h> (see ioctl(2)):

FIOSNBIO If the int with the address arg is non-zero, the socket is put into non-blocking mode. Otherwise, the socket is put into blocking mode. Blocking mode is the default. The FIONBIO request is equivalent to the FIOSNBIO request, although using FIONBIO is not recommended. See accept(2), connect(2), recv(2), and send(2) for an explanation of how non-blocking mode is used.

FIONREAD For SOCK_STREAM sockets, the number of bytes currently readable from this socket is returned in the integer with the address arg. For SOCK_DGRAM sockets, the number of bytes currently readable, plus the size of the sockaddr structure (defined in <sys/socket.h>), is returned in the integer with the address arg.

SIOCATMARK For SOCK_STREAM TCP sockets, on return the integer with the address arg is non-zero if the inbound TCP stream has been read up to where the out-of-band data byte starts; otherwise the inbound TCP stream has not yet been read up to where the out-of-band data byte starts. For sockets other than SOCK_STREAM TCP sockets, on return the integer with the address arg is always zero.

SIOCSPGRP This request sets the process group or process ID associated with the socket to be the value of the integer with the address arg. A process group or process ID associated with the socket in this manner is signaled when the state of the socket changes: SIGURG is delivered upon the receipt of out-of-band data; SIGIO is delivered if the socket is asynchronous, as described in FIOASYNC below. If the value of the integer with the address arg is positive, the signal is sent to the process whose process ID matches the value specified. If the value is negative, the signal is sent to all the processes that have a process group equal to the absolute value of the value specified. If the value is zero, no signal is sent to any process. It is necesary to issue this request with a non-zero integer value to enable the signal delivery mechanism described above; the default for the process group or process ID value is zero.

SIOCGPGRP This request returns the process group or process ID associated with the socket in the integer with the address arg. See the explanation for SIOCSPGRP above for more details on the meaning of the integer value returned.

FIOASYNC If the integer whose address is arg is non-zero, this request sets the state of the socket as asynchronous. Otherwise, the socket is put into synchronous mode (the default). Asynchronous mode enables the delivery of the SIGIO signal when:

• New data arrives, or

• For connection-oriented protocols, whenever additional outgoing buffer space becomes available, or when the connection is established or broken.

The process group or process ID associated with the socket must be non-zero in order for SIGIO signals to be sent; the signal is delivered according to the semantics of SIOCSPGRP descibed above.

The fcntl(2) O_NDELAY and O_NONBLOCK flags (defined in <sys/file.h>) are supported by sockets. If the O_NONBLOCK flag is set, the socket is put into POSIX -style non-blocking mode. If the O_NDELAY flag is set, the socket is put into non-blocking mode. Otherwise, the socket is put into blocking mode. Blocking mode is the default. See accept(2), connect(2), recv(2), and send(2) for an explanation of how these form of non-blocking mode is used.

Since both the fcntl() O_NONBLOCK and O_NDELAY flags and ioctl() FIOSNBIO requests are supported, some clarification on how these features interact is necessary. If the O_NONBLOCK or O_NDELAY flag has been set, recv() and send() requests behave accordingly, regardless of any FIOSNBIO requests. If neither the O_NONBLOCK flag nor the O_NDELAY flag has been set, FIOSNBIO requests control the the behavior of recv() and send().

DEPENDENCIES

This entry describes the use of the TCP protocol as it applies to the Berkeley Interprocess Communication utility. It does not apply to the use of TCP for the Net IPC utility. Refer to the NetIPC Programmer’s Guide for information about NetIPC.

AF_CCITT Only

Only the FIOSNBIO, FIONREAD, SIOCGPGRP, and SIOCSPGRP ioctl() requests are defined for af_ccitt sockets. See socketx25(7).

AUTHOR

socket was developed by the University of California, Berkeley.

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