154 lines
4.3 KiB
Groff
154 lines
4.3 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)ioctl.2 8.2 (Berkeley) 12/11/93
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.\"
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.Dd September 11, 2013
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.Dt IOCTL 2
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.Os
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.Sh NAME
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.Nm ioctl
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.Nd control device
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/ioctl.h
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.Ft int
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.Fn ioctl "int fd" "unsigned long request" ...
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.Sh DESCRIPTION
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The
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.Fn ioctl
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system call manipulates the underlying device parameters of special files.
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In particular, many operating
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characteristics of character special files (e.g.\& terminals)
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may be controlled with
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.Fn ioctl
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requests.
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The argument
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.Fa fd
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must be an open file descriptor.
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.Pp
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The third argument to
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.Fn ioctl
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is traditionally named
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.Va "char *argp" .
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Most uses of
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.Fn ioctl ,
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however, require the third argument to be a
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.Vt caddr_t
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or an
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.Vt int .
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.Pp
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An
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.Fn ioctl
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.Fa request
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has encoded in it whether the argument is an
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.Dq in
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argument
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or
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.Dq out
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argument, and the size of the argument
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.Fa argp
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in bytes.
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Macros and defines used in specifying an ioctl
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.Fa request
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are located in the file
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.In sys/ioctl.h .
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.Sh GENERIC IOCTLS
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Some generic ioctls are not implemented for all types of file
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descriptors.
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These include:
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.Bl -tag -width "xxxxxx"
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.It Dv FIONREAD int
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Get the number of bytes that are immediately available for reading.
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.It Dv FIONWRITE int
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Get the number of bytes in the descriptor's send queue.
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These bytes are data which has been written to the descriptor but
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which are being held by the kernel for further processing.
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The nature of the required processing depends on the underlying device.
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For TCP sockets, these bytes have not yet been acknowledged by the
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other side of the connection.
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.It Dv FIONSPACE int
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Get the free space in the descriptor's send queue.
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This value is the size of the send queue minus the number of bytes
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being held in the queue.
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Note: while this value represents the number of bytes that may be
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added to the queue, other resource limitations may cause a write
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not larger than the send queue's space to be blocked.
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One such limitation would be a lack of network buffers for a write
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to a network connection.
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.El
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.Sh RETURN VALUES
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If an error has occurred, a value of -1 is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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The
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.Fn ioctl
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa fd
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argument
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is not a valid descriptor.
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.It Bq Er ENOTTY
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The
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.Fa fd
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argument
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is not associated with a character
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special device.
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.It Bq Er ENOTTY
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The specified request does not apply to the kind
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of object that the descriptor
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.Fa fd
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references.
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.It Bq Er EINVAL
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The
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.Fa request
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or
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.Fa argp
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argument
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is not valid.
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.It Bq Er EFAULT
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The
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.Fa argp
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argument
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points outside the process's allocated address space.
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.El
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.Sh SEE ALSO
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.Xr execve 2 ,
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.Xr fcntl 2 ,
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.Xr intro 4 ,
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.Xr tty 4
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.Sh HISTORY
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The
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.Fn ioctl
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function appeared in
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.At v7 .
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