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IOCTL(2)		    BSD	System Calls Manual		      IOCTL(2)

NAME
     ioctl -- control device

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/ioctl.h>

     int
     ioctl(int d, unsigned long	request, ...);

DESCRIPTION
     The ioctl() function manipulates the underlying device parameters of spe-
     cial files.  In particular, many operating	characteristics	of character
     special files (e.g. terminals) may	be controlled with ioctl() requests.
     The argument d must be an open file descriptor.

     An	ioctl()	request	has encoded in it whether the argument is an "in",
     "out", or "inout" parameter, and the size of the first variadic argument
     in	bytes.	Note that there	can be only one	variadic argument but cannot
     be	represented as a void *	argument in the	prototype because this would
     require a cast to pass integral types without warnings.  Macros and de-
     fines used	in specifying an ioctl() request are located in	the header
     <sys/ioctl.h>.

GENERIC	IOCTLS
     Some ioctls are applicable	to any file descriptor.	 These include:

     FIOCLEX
	     Set close-on-exec flag.  The file will be closed when exec(3) is
	     invoked (This is equivalent to fcntl() F_SETFD FD_CLOEXEC and the
	     fcntl() form should be preferred).

     FIONCLEX
	     Clear close-on-exec flag.	The file will remain open across
	     exec(3) (This is equivalent to fcntl() F_SETFD 0 and the fcntl()
	     form should be preferred).

     Some generic ioctls are not implemented for all types of file descrip-
     tors.  These include:

     FIONREAD int
	     Get the number of bytes that are immediately available for	read-
	     ing.

     FIONWRITE int
	     Get the number of bytes in	the descriptor's send queue.  These
	     bytes are data which has been written to the descriptor but which
	     are being held by the kernel for further processing.  The nature
	     of	the required processing	depends	on the underlying device.  For
	     tty devices, these	bytes are typically queued for delivery	to the
	     tty hardware.  For	TCP sockets, these bytes have not yet been ac-
	     knowledged	by the other side of the connection.  For files, this
	     operation always returns zero as files do not have	send queues.

     FIONSPACE int
	     Get the free space	in the descriptor's send queue.	 This value is
	     the size of the send queue	minus the number of bytes being	held
	     in	the queue.  Note: while	this value represents the number of
	     bytes that	may be added to	the queue, other resource limitations
	     may cause a write not larger than the send	queue's	space to be
	     blocked.  One such	limitation would be a lack of network buffers
	     for a write to a network connection.

     FIONBIO int
	     Set non-blocking I/O mode if the argument is non-zero.  In	non-
	     blocking mode, read(2) or write(2)	calls return -1	and set	errno
	     to	EAGAIN immediately when	no data	is available (This is equiva-
	     lent to fcntl() F_SETFL O_NONBLOCK	and the	fcntl()	form should be
	     preferred).

     FIOASYNC int
	     Set asynchronous I/O mode if the argument is non-zero (This is
	     equivalent	to fcntl() F_SETFL O_ASYNC and the fcntl() form	should
	     be	preferred).  In	asynchronous mode, the process or process
	     group specified by	FIOSETOWN will start receiving SIGIO signals
	     when data is available.  The SIGIO	signal will be delivered when
	     data is available on the file descriptor.

     FIOSETOWN,	FIOGETOWN int
	     Set/get the process or the	process	group (if negative) that
	     should receive SIGIO signals when data is available (This is
	     equivalent	to fcntl() F_SETOWN pid_t and the fcntl	form should be
	     preferred).

RETURN VALUES
     If	an error has occurred, a value of -1 is	returned and errno is set to
     indicate the error.

ERRORS
     ioctl() will fail if:

     [EBADF]		d is not a valid descriptor.

     [EFAULT]		argp points outside the	process's allocated address
			space.

     [EINVAL]		request	or argp	is not valid.

     [ENOTTY]		d is not associated with a character special device;
			or the specified request does not apply	to the kind of
			object that the	descriptor d references.

SEE ALSO
     mt(1), execve(2), fcntl(2), intro(4), tty(4)

HISTORY
     An	ioctl()	function call appeared in Version 7 AT&T UNIX.

BSD			       December	19, 2010			   BSD

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | GENERIC IOCTLS | RETURN VALUES | ERRORS | SEE ALSO | HISTORY

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