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IOCTL(2)                  NetBSD 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, void *argp);


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''
     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>.


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.

     FIONCLEX
             Clear close-on-exec flag.  The file will remain open across
             exec(3).

     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.

     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.

     FIOASYNC int
             Set asynchronous I/O mode if the argument is non-zero.  In asyn-
             chronous mode, the process or process group specified by
             FIOSETOWN will start receiving SIGIO signals when data is avail-
             able.  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.


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.

     [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.

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


SEE ALSO

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


HISTORY

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

NetBSD 2.0                      August 11, 2002                     NetBSD 2.0

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