socket(7)

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.

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.

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.

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 necessary 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.

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.

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 either of the following conditions is met.

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 described above.