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NetBSD 6.1.5 - man page for ioctl (netbsd section 2)

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

     ioctl -- control device

     Standard C Library (libc, -lc)

     #include <sys/ioctl.h>

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

     The ioctl() function manipulates the underlying device parameters of special files.  In par-
     ticular, 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 pro-
     totype because this would require a cast to pass integral types without warnings.	Macros
     and defines used in specifying an ioctl() request are located in the header <sys/ioctl.h>.

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

	     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).

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

     Some generic ioctls are not implemented for all types of file descriptors.  These include:

     FIONREAD int
	     Get the number of bytes that are immediately available for reading.

     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 fur-
	     ther 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 acknowledged 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 con-

     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 equivalent 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 sig-
	     nals when data is available.  The SIGIO signal will be delivered when data is avail-
	     able on the file descriptor.

	     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).

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

     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 refer-

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

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

BSD					December 19, 2010				      BSD

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