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RedHat 9 (Linux i386) - man page for ioctl (redhat section 2)

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 charac- ter 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 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. 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.
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), mt(4), sd(4), tty(4) BSD Man Page 2000-09-21 IOCTL(2)