trusty (2) ioctl.2.gz

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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 character 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 ioctl() requests use the return value as an output parameter
       and return a nonnegative value on success.  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.

       EINVAL Request or argp is not valid.

       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.


CONFORMING TO
       No single standard.  Arguments, returns, and semantics of ioctl() 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.


NOTES
       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.


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


COLOPHON
       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.