IOCTL(2) IOCTL(2)
NAME
ioctl, stty, gtty - miscellaneous stream control operations
SYNOPSIS
#include <sgtty.h>
ioctl(fildes, request, argp)
struct sgttyb *argp;
stty(fildes, argp)
struct sgttyb *argp;
gtty(fildes, argp)
struct sgttyb *argp;
DESCRIPTION
Ioctl performs a variety of functions on special files and
streams. The writeups of various devices in section 4 dis-
cuss how ioctl applies to them.
For certain status setting and status inquiries about termi-
nal devices, the functions stty and gtty are equivalent to
ioctl(fildes, TIOCSETP, argp);
ioctl(fildes, TIOCGETP, argp);
respectively; see ttyld(4).
The following two standard calls, however, apply to any open
file. The defined constant NULL has value 0.
ioctl(fildes, FIOCLEX, NULL);
ioctl(fildes, FIONCLEX, NULL);
The first causes the file to be closed automatically upon a
successful exec(2); the second causes the file to be left
open.
The following call applies to any stream file descriptor:
ioctl(fildes, FIONREAD, &count);
It returns, in the integer count, the number of characters
available for reading from fildes.
The following calls provide an advisory file locking facil-
ity, and apply to any open file:
ioctl(fildes, FIOALOCK, NULL);
ioctl(fildes, FIOAUNLOCK, NULL);
IOCTL(2) IOCTL(2)
ioctl(fildes, FIOAISLOCK, NULL);
FIOALOCK either sets an advisory lock, or indicates that
this file is already locked by returning -1, with errno set
to EPERM.
FIOAUNLOCK either clears an advisory lock, or indicates that
the file is locked by another instance of open by returning
-1, with errno set to EPERM.
FIOAISLOCK returns 0 for a file with no advisory lock set, 1
for a file with an advisory lock set using another instance
of open, or 2 for a file with an advisory lock set on the
current instance of open. File descriptors belong to the
same instance when they are copied by dup(2) or fork(2).
Locks are detectable only through these calls, and have no
effect on IO or ability to open files.
SEE ALSO
stty(1), ttyld(4), proc(4), exec(2)
DIAGNOSTICS
Except where otherwise stated, 0 is returned if the call is
successful; -1 if the file descriptor does not refer to the
kind of file for which it was intended, or if request
attempts to modify the state of an unwritable file.
BUGS
Strictly speaking, since ioctl may be extended in different
ways to devices with different properties, argp should have
an open-ended declaration like
union { struct sgttyb ...; ... } *argp;
The important thing is that the size is fixed by `struct
sgttyb'.
Ioctl requests vary among UNIX systems; undisciplined use is
likely to compromise portability.