ioctl

IOCTL(2)		  Linux Programmer’s Manual		     IOCTL(2)



NAME
       ioctl - control device

SYNOPSIS
       #include <sys/ioctl.h>

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

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

       The second argument is a device-dependent  request  code.   The	third
       argument	 is  an	 untyped  pointer to memory.  It’s traditionally char
       *argp (from the days before void * was valid C), and will be so	named
       for this discussion.

       An  ioctl  request  has	encoded	 in  it whether the argument is an in
       parameter or out parameter, and the  size  of  the  argument  argp  in
       bytes.	Macros	and  defines  used in specifying an ioctl request are
       located in the file <sys/ioctl.h>.

RETURN VALUE
       Usually, on success zero is returned.  A few  ioctls  use  the  return
       value  as  an  output parameter and return a nonnegative value on suc-
       cess.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EBADF  d is not a valid descriptor.

       EFAULT argp references an inaccessible memory area.

       ENOTTY d is not associated with a character special device.

       ENOTTY The specified request does not apply to the kind of object that
	      the descriptor d references.

       EINVAL Request or argp is not valid.

NOTE
       In  order  to use this call, one needs an open file descriptor.	Often
       the open(2) call has unwanted side effects, that can be avoided	under
       Linux by giving it the O_NONBLOCK flag.

CONFORMING TO
       No  single  standard.   Arguments,  returns, and semantics of ioctl(2)
       vary according to the device driver in question (the call is used as a
       catch-all  for  operations  that don’t cleanly fit the Unix stream I/O
       model). See ioctl_list(2) for a list of many of the known ioctl calls.
       The ioctl function call appeared in Version 7 AT&T Unix.

SEE ALSO
       execve(2), fcntl(2), ioctl_list(2), open(2), mt(4), sd(4), tty(4)



BSD Man Page			  2000-09-21			     IOCTL(2)