V10/man/man2/ioctl.2

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.TH IOCTL 2
.CT 2 file_io file_inq_creat
.SH NAME
ioctl \(mi miscellaneous control operations
.SH SYNOPSIS
.nf
.B #include <sys/filio.h>
.PP
.B int ioctl(fildes, request, param)
.B void *param;
.fi
.SH DESCRIPTION
.I Ioctl
performs a variety of
.I requests
on open files,
most applying only to particular device files.
The writeups of various devices
in section 4 discuss how
.I ioctl
applies to them;
see
.IR stream (4)
in particular
for operations applying to
communication devices.
.PP
.I Param
points to a parameter buffer.
Some
.I requests
read data from the buffer;
others write data to the buffer;
some do both.
The buffer's size varies according to the request.
A few provide meaningful data
in the return value from
.I ioctl
as well;
others return a conventional value of
0 for success,
\-1 for failure.
.PP
Requests for different drivers
are defined in different header files.
Two standard calls,
defined in
.BR <sys/filio.h> ,
apply to any open file:
.IP
.L
ioctl(fildes, FIOCLEX, (void *)0);
.br
.L
ioctl(fildes, FIONCLEX, (void *)0);
.LP
The first causes the file to be closed automatically upon
a successful
.IR exec (2);
the second causes the file to be left open.
.SH "SEE ALSO"
.IR exec (2),
.IR stream (4)
.SH DIAGNOSTICS
.BR EBADF ,
.BR EFAULT ,
.BR EIO ,
.BR ENODEV ,
.BR ENOTTY
.SH BUGS
.I Ioctl
requests vary among UNIX systems;
undisciplined use is likely to compromise portability.
.br
The size of the parameter buffer
should be an explicit argument.