mirror of https://github.com/mkerrisk/man-pages
209 lines
6.2 KiB
Groff
209 lines
6.2 KiB
Groff
.\" Copyright (c) 1980, 1991 Regents of the University of California.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\" %%%LICENSE_END
|
|
.\"
|
|
.\" @(#)ioctl.2 6.4 (Berkeley) 3/10/91
|
|
.\"
|
|
.\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
|
|
.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
|
|
.\" Modified 1999-06-25 by Rachael Munns <vashti@dream.org.uk>
|
|
.\" Modified 2000-09-21 by Andries Brouwer <aeb@cwi.nl>
|
|
.\"
|
|
.TH IOCTL 2 2020-04-11 "Linux" "Linux Programmer's Manual"
|
|
.SH NAME
|
|
ioctl \- control device
|
|
.SH SYNOPSIS
|
|
.B #include <sys/ioctl.h>
|
|
.PP
|
|
.BI "int ioctl(int " fd ", unsigned long " request ", ...);"
|
|
.\" POSIX says 'request' is int, but glibc has the above
|
|
.\" See https://bugzilla.kernel.org/show_bug.cgi?id=42705
|
|
.SH DESCRIPTION
|
|
The
|
|
.BR ioctl ()
|
|
system call manipulates the underlying device parameters of special files.
|
|
In particular, many operating characteristics of character special files
|
|
(e.g., terminals) may be controlled with
|
|
.BR ioctl ()
|
|
requests.
|
|
The argument
|
|
.I fd
|
|
must be an open file descriptor.
|
|
.PP
|
|
The second argument is a device-dependent request code.
|
|
The third argument is an untyped pointer to memory.
|
|
It's traditionally
|
|
.BI "char *" argp
|
|
(from the days before
|
|
.B "void *"
|
|
was valid C), and will be so named for this discussion.
|
|
.PP
|
|
An
|
|
.BR ioctl ()
|
|
.I request
|
|
has encoded in it whether the argument is an
|
|
.I in
|
|
parameter or
|
|
.I out
|
|
parameter, and the size of the argument
|
|
.I argp
|
|
in bytes.
|
|
Macros and defines used in specifying an
|
|
.BR ioctl ()
|
|
.I request
|
|
are located in the file
|
|
.IR <sys/ioctl.h> .
|
|
See NOTES.
|
|
.SH RETURN VALUE
|
|
Usually, on success zero is returned.
|
|
A few
|
|
.BR ioctl ()
|
|
requests use the return value as an output parameter
|
|
and return a nonnegative value on success.
|
|
On error, \-1 is returned, and
|
|
.I errno
|
|
is set appropriately.
|
|
.SH ERRORS
|
|
.TP
|
|
.B EBADF
|
|
.I fd
|
|
is not a valid file descriptor.
|
|
.TP
|
|
.B EFAULT
|
|
.I argp
|
|
references an inaccessible memory area.
|
|
.TP
|
|
.B EINVAL
|
|
.I request
|
|
or
|
|
.I argp
|
|
is not valid.
|
|
.TP
|
|
.B ENOTTY
|
|
.I fd
|
|
is not associated with a character special device.
|
|
.TP
|
|
.B ENOTTY
|
|
The specified request does not apply to the kind of object that the
|
|
file descriptor
|
|
.I fd
|
|
references.
|
|
.SH CONFORMING TO
|
|
No single standard.
|
|
Arguments, returns, and semantics of
|
|
.BR ioctl ()
|
|
vary according to the device driver in question (the call is used as a
|
|
catch-all for operations that don't cleanly fit the UNIX stream I/O
|
|
model).
|
|
.PP
|
|
The
|
|
.BR ioctl ()
|
|
system call appeared in Version 7 AT&T UNIX.
|
|
.SH NOTES
|
|
In order to use this call, one needs an open file descriptor.
|
|
Often the
|
|
.BR open (2)
|
|
call has unwanted side effects, that can be avoided under Linux
|
|
by giving it the
|
|
.B O_NONBLOCK
|
|
flag.
|
|
.\"
|
|
.SS ioctl structure
|
|
.\" added two sections - aeb
|
|
Ioctl command values are 32-bit constants.
|
|
In principle these constants are completely arbitrary, but people have
|
|
tried to build some structure into them.
|
|
.PP
|
|
The old Linux situation was that of mostly 16-bit constants, where the
|
|
last byte is a serial number, and the preceding byte(s) give a type
|
|
indicating the driver.
|
|
Sometimes the major number was used: 0x03
|
|
for the
|
|
.B HDIO_*
|
|
ioctls, 0x06 for the
|
|
.B LP*
|
|
ioctls.
|
|
And sometimes
|
|
one or more ASCII letters were used.
|
|
For example,
|
|
.B TCGETS
|
|
has value
|
|
0x00005401, with 0x54 = \(aqT\(aq indicating the terminal driver, and
|
|
.B CYGETTIMEOUT
|
|
has value 0x00435906, with 0x43 0x59 = \(aqC\(aq \(aqY\(aq
|
|
indicating the cyclades driver.
|
|
.PP
|
|
Later (0.98p5) some more information was built into the number.
|
|
One has 2 direction bits
|
|
(00: none, 01: write, 10: read, 11: read/write)
|
|
followed by 14 size bits (giving the size of the argument),
|
|
followed by an 8-bit type (collecting the ioctls in groups
|
|
for a common purpose or a common driver), and an 8-bit
|
|
serial number.
|
|
.PP
|
|
The macros describing this structure live in
|
|
.I <asm/ioctl.h>
|
|
and are
|
|
.B _IO(type,nr)
|
|
and
|
|
.BR "{_IOR,_IOW,_IOWR}(type,nr,size)" .
|
|
They use
|
|
.I sizeof(size)
|
|
so that size is a
|
|
misnomer here: this third argument is a data type.
|
|
.PP
|
|
Note that the size bits are very unreliable: in lots of cases
|
|
they are wrong, either because of buggy macros using
|
|
.IR sizeof(sizeof(struct)) ,
|
|
or because of legacy values.
|
|
.PP
|
|
Thus, it seems that the new structure only gave disadvantages:
|
|
it does not help in checking, but it causes varying values
|
|
for the various architectures.
|
|
.SH SEE ALSO
|
|
.BR execve (2),
|
|
.BR fcntl (2),
|
|
.BR ioctl_console (2),
|
|
.BR ioctl_fat (2),
|
|
.BR ioctl_ficlonerange (2),
|
|
.BR ioctl_fideduperange (2),
|
|
.BR ioctl_fslabel (2),
|
|
.BR ioctl_getfsmap (2),
|
|
.BR ioctl_iflags (2),
|
|
.BR ioctl_ns (2),
|
|
.BR ioctl_tty (2),
|
|
.BR ioctl_userfaultfd (2),
|
|
.BR open (2),
|
|
.\" .BR mt (4),
|
|
.BR sd (4),
|
|
.BR tty (4)
|