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 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(2,3,n) file(1,n) 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(5,8)
for this discussion.
An ioctl request has encoded in(1,8) it whether the argument is an in(1,8) param-
eter or out parameter, and the size of the argument argp in(1,8) bytes.
Macros and defines used in(1,8) specifying an ioctl request are located in(1,8)
the file(1,n) <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(8,n), -1 is returned, and errno is set(7,n,1 builtins) 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.
NOTE
In order to use this call, one needs an open(2,3,n) file(1,n) descriptor. Often
the open(2,3,n)(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(1,8) 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(1,8) Version 7 AT&T Unix.
SEE ALSO
execve(2), fcntl(2), ioctl_list(2), open(2,3,n)(2), mt(4), sd(4), tty(1,4)(4)
BSD Man Page 2000-09-21 IOCTL(2)