NAME

ioctl − control device

SYNOPSIS

#include <sys/ioctl.h>

ioctl(d, request, argp)
int d;
int request;
char ∗argp;

DESCRIPTION

Ioctl performs a variety of functions on open descriptors.  In particular, many operating characteristics of character special files (e.g. terminals) may be controlled with ioctl requests.  The writeups of various devices in section 4 discuss how ioctl applies to them. 

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>.

The following calls apply to any descriptor:

ioctl(d, FIOCLEX, 0);
ioctl(d, FIONCLEX, 0);

The first causes the file to be closed automatically during a successful exec operation; the second reverses the effect of the first. 

ioctl(d, FIONREAD, &count)
int count;

returns, in the longword count the number of characters available for reading from fildes. 

RETURN VALUE

If an error has occurred, a value of −1 is returned and errno is set to indicate the error. 

ERRORS

Ioctl will fail if one or more of the following are true:

[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 which the descriptor d references. 

[EINVAL] Request or argp is not valid. 

SEE ALSO

dk(4), mt(4), tty(4)

BUGS

The following call is a temporary replacement for the as yet not implemented setdopt(2) call:

ioctl(fildes, FIONBIO, onoff);
int ∗onoff;

The parameter onoff specifies whether non-blocking i/o is desired on the specified descriptor.  This applies to terminals, pipes, pseudo-terminals and sockets and specifies that operations are to return EWOULDBLOCK rather than blocking.  A select(2) operation may be used to determine when i/o is possible without busy polling.

Sun System Release 0.3  —  13 February 1983