IOCTL(2) IOCTL(2)
NAME
ioctl - miscellaneous control operations
SYNOPSIS
#include <sys/filio.h>
int ioctl(fildes, request, param)
void *param;
DESCRIPTION
Ioctl performs a variety of requests on open files, most
applying only to particular device files. The writeups of
various devices in section 4 discuss how ioctl applies to
them; see stream(4) in particular for operations applying to
communication devices.
Param points to a parameter buffer. Some 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 ioctl
as well; others return a conventional value of 0 for suc-
cess, -1 for failure.
Requests for different drivers are defined in different
header files. Two standard calls, defined in <sys/filio.h>,
apply to any open file:
ioctl(fildes, FIOCLEX, (void *)0);
ioctl(fildes, FIONCLEX, (void *)0);
The first causes the file to be closed automatically upon a
successful exec(2); the second causes the file to be left
open.
SEE ALSO
exec(2), stream(4)
DIAGNOSTICS
EBADF, EFAULT, EIO, ENODEV, ENOTTY
BUGS
Ioctl requests vary among UNIX systems; undisciplined use is
likely to compromise portability.
The size of the parameter buffer should be an explicit argu-
ment.