ioctl-sockets

Provides an interface and control over magnetic tape devices. In the case of magnetic tape devices, the ioctl() function provides an interface for issuing various control commands to opened tape devices. The ioctl() operations can be used to position the magnetic tape, and to determine the tape device status.

Syntax

   int ioctl(fildes, request, arg)

   int fildes;

   int request;

   void *arg;

Parameters

fildes

The socket descriptor.

request

This parameter specifies which command to perform on the socket. The commands are defined in <sys/ioctl.h>. The different commands that are available are described below.

FIONREAD: Gets the number of bytes that are readable from the socket. For TCP sockets, this is the total number of bytes queued to the socket. For UDP sockets, this is the total number of bytes queued in each datagram and the sum of all the source address structures. The arg parameter, will contain the address of the integer with the number of bytes readable.
FIOSNBIO: Enables or disables non-blocking I/O for the socket. If the integer whose address is arg is not zero, then non-blocking I/O is enabled. When non-blocking I/O is enabled, subsequent read and write requests to the socket are prevented from blocking whether the request succeeds or fails. If the integer whose address is arg is zero, then non-blocking I/O is disabled.
FIONBIO: This command is same as the FIOSNBIO command.
FIOGNBIO: Gets the status of non-blocking i/o. If non-blocking i/o is enabled for the socket, then the integer whose address is arg is set to 1. If non-blocking i/o is disabled, the integer is set to zero.
FIOGSAIOSTAT: If asynchronous signaling is enabled for the socket, then the integer whose address is arg is set to 1. If the asynchronous state is disabled, the integer is set to zero.
SIOCATMARK: For SOCK_STREAM TCP sockets, upon return if the integer whose address is arg is not zero, then the inbound TCP stream has been read up to where the out-of-band data byte starts. If the integer at address arg is zero, then the inbound TCP stream has not yet been read up to where the out-of-band data byte starts. For non-TCP sockets, upon return the integer with the address arg is always zero.
SIOCSPGRP: This command sets the process group or process ID associated with the socket to be the value of the integer whose address is arg. If the value of the integer is positive, then a signal is sent to the process with the matching process ID value when the state of the socket changes. If the value is negative, then a signal is sent to all processes that have a process group equal to the absolute value of the specified value when the socket state changes. If the value of the integer with address arg is zero, no signal is sent to any processes when the socket state changes.
SIOCGPGRP: This command returns the process group or process ID associated with the socket in the integer whose address is arg. If the integer is positive, then the value returned corresponds to a process ID. If the integer is negative, then the value returned corresponds to all processes that have a process group equal to the absolute value of that value.

arg

This parameter is the address of the integer that the specified request needs in order to perform its function. Depending on the type of request specified, the integer can represent a variety of values. See the appropriate request command for an explanation of the value that the integer will represent in that context.

Return Values

0: The function completes successfully.
-1: If an error occurs, a value of -1 is returned by the function and the global variable errno is set with the resultant error.

Description

Sockets are communication endpoints that allow processes to communicate either locally or remotely. For sockets, the ioctl() function provides an interface for setting different characteristics for a socket, and retrieving information on a socket.

Implementation Considerations

There will not be any implementation defined items in the sockets portion of ioctl().

There are no mixed environment issues for the sockets portion of ioctl().

Errors

If an error occurs, errno is set to one of the following values:

`EBADF`	CAUSE	The argument `fildes` is not a valid open file descriptor.
	ACTION	Check to see if `fildes` has been altered or if `fildes` is not initialized.	`EFAULT`	CAUSE	The system detected a NULL address while attempting to use the `arg` parameter passed by the caller.
	ACTION	Check to see if the pointer used is initialized and/or not equal to NULL.
`EINTR`	CAUSE	Once this function is executing an intrinsic, no signal interruption may occur. Signal interrupts can only occur in the library portion of the code.
	ACTION	Check the state of the socket referenced by `fildes`.
`EINVAL`	CAUSE	The `request` parameter or the `arg` parameter is invalid, or a socket type that is not supported was specified.
	ACTION	Validate the `request` and `arg` values; check if the socket type is supported.

ioctl-sockets

Technical documentation

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