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the number of bytes in the send queue, and FIONSPACE reports the number of free bytes in the send queue. These ioctls permit applications to monitor file descriptor transmission dynamics. In examining prior art, FIONWRITE exists with the semantics given here. FIONSPACE is provided so that programs may easily determine how much space is left in the send queue; they do not need to know the send queue size. The fact that a write may block even if there is enough space in the send queue for it is noted in the documentation. FIONWRITE functionality may be used to implement TIOCOUTQ for Linux emulation - Linux extended this ioctl to sockets, even though they are not ttys.
179 lines
5.2 KiB
Groff
179 lines
5.2 KiB
Groff
.\" $NetBSD: ioctl.2,v 1.19 2004/11/06 02:03:20 wrstuden Exp $
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.\"
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.\" 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 August 11, 2002
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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 d" "unsigned long request" "void *argp"
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.Sh DESCRIPTION
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The
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.Fn ioctl
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function 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 d
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must be an open file descriptor.
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.Pp
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An 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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parameter
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or
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.Dq out
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parameter, 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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.Ao Pa sys/ioctl.h Ac .
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.Sh GENERIC IOCTLS
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Some ioctls are applicable to any file descriptor.
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These include:
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.Bl -tag -width "xxxxxx"
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.It Dv FIOCLEX
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Set close-on-exec flag.
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The file will be closed when
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.Xr exec 3
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is invoked.
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.It Dv FIONCLEX
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Clear close-on-exec flag.
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The file will remain open across
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.Xr exec 3 .
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.El
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.Pp
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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 tty devices, these bytes are typically queued for delivery
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to the tty hardware.
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For TCP sockets, these bytes have not yet been acknolwedged by the
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other side of the connection.
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For files, this operation always returns zero as files do not have
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send queues.
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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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.It Dv FIONBIO "int"
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Set non-blocking I/O mode if the argument is non-zero.
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In non-blocking mode,
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.Xr read 2
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or
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.Xr write 2
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calls return \-1 and set
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.Va errno
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to
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.Er EAGAIN
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immediately when no data is available.
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.It Dv FIOASYNC "int"
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Set asynchronous I/O mode if the argument is non-zero.
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In asynchronous mode, the process or process group specified by
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.Dv FIOSETOWN
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will start receiving
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.Dv SIGIO
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signals when data is available.
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The
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.Dv SIGIO
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signal will be delivered when data is available on the file
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descriptor.
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.It Dv FIOSETOWN, FIOGETOWN "int"
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Set/get the process or the process group (if negative) that should receive
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.Dv SIGIO
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signals when data is available.
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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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.Fn ioctl
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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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.Fa d
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is not a valid descriptor.
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.It Bq Er ENOTTY
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.Fa d
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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 d
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references.
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.It Bq Er EINVAL
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.Fa request
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or
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.Fa argp
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is not valid.
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.It Bq Er EFAULT
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.Fa argp
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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 mt 1 ,
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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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An
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.Fn ioctl
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function call appeared in
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.At v7 .
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