4.1cBSD/usr/man/man2/ioctl.2

.TH IOCTL 2 2/13/83
.SH NAME
ioctl \- control device
.SH SYNOPSIS
.nf
.ft B
#include <sys/ioctl.h>
.PP
.ft B
ioctl(d, request, argp)
int d;
int request;
char *argp;
.fi
.ft R
.SH DESCRIPTION
.I 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
.I ioctl
requests.
The writeups of various devices in section 4 discuss how
.I ioctl
applies to them.
.PP
An  ioctl
.I request
has encoded in it whether the argument is an \*(lqin\*(rq parameter
or \*(lqout\*(rq parameter, and the size of the argument \fIargp\fP in bytes.
Macros and defines used in specifying an ioctl
.I request
are located in the file
.IR <sys/ioctl.h> .
.PP
The following calls apply to any descriptor:
.RS
.ft B
.nf
ioctl(d, FIOCLEX, 0);
ioctl(d, FIONCLEX, 0);
.fi
.ft R
.RE
.LP
The first causes the file to be closed automatically during a successful
.I exec
operation; the second reverses the effect of the first.
.PP
.RS
.ft B
.nf
ioctl(d, FIONREAD, &count)
int count;
.fi
.ft R
.RE
.LP
returns, in the longword
.I count
the number of characters available for reading from
.I fildes.
.SH "RETURN VALUE
If an error has occurred, a value of \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.I Ioctl
will fail if one or more of the following are true:
.TP 15
[EBADF]
\fID\fP is not a valid descriptor.
.TP 15
[ENOTTY]
\fID\fP is not associated with a character
special device.
.TP 15
[ENOTTY]
The specified request does not apply to the kind
of object which the descriptor \fId\fP references.
.TP 15
[EINVAL]
\fIRequest\fP or \fIargp\fP is not valid.
.SH "SEE ALSO"
dk(4), mt(4), tty(4)
.SH BUGS
The following call is a temporary replacement for the as yet not
implemented
.IR setdopt (2)
call:
.PP
.RS
.ft B
.nf
ioctl(fildes, FIONBIO, onoff);
int *onoff;
.ft R
.fi
.RE
.LP
The parameter 
.I 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
.IR select (2)
operation may be used to determine when i/o is possible without busy polling.