203 lines
5.5 KiB
Groff
203 lines
5.5 KiB
Groff
.\" Copyright (c) 1998 Terry Lambert
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.\" 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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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.\" $FreeBSD$
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.\"
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.Dd November 17, 1998
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.Dt AIO_READ 2
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.Os
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.Sh NAME
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.Nm aio_read
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.Nd asynchronous read from a file (REALTIME)
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <time.h>
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.Fd #include <aio.h>
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.Ft int
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.Fn aio_read "struct aiocb *iocb"
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.Sh DESCRIPTION
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The
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.Fn aio_read
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function allows the calling process to read
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.Fa iocb->aio_nbytes
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from the descriptor
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.Fa iocb->aio_fildes
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beginning at the offset
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.Fa iocb->aio_offset
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into the buffer pointed to by
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.Fa iocb->aio_buf .
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The call returns immediately after the read request has
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been enqueued to the descriptor; the read may or may not have
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completed at the time the call returns.
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.Pp
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If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it,
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then the enqueued operation is submitted at a priority equal to that
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of the calling process minus
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.Fa iocb->aio_reqprio .
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.Pp
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The
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.Fa iocb->aio_lio_opcode
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is ignored by the
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.Fn aio_read
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call.
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.Pp
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The
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.Fa iocb
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pointer may be subsequently used as an argument to
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.Fn aio_return
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and
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.Fn aio_error
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in order to determine return or error status for the enqueued operation
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while it is in progress.
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.Pp
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If the request could not be enqueued (generally due to invalid arguments),
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then the call returns without having enqueued the request.
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.Pp
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If the request is successfully enqueued, the value of
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.Fa iocb->aio_offset
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can be modified during the request as context, so this value must
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not be referenced after the request is enqueued.
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.Sh RESTRICTIONS
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The Asynchronous I/O Control Block structure pointed to by
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.Fa iocb
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and the buffer that the
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.Fa iocb->aio_buf
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member of that structure references must remain valid until the
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operation has completed. For this reason, use of auto (stack) variables
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for these objects is discouraged.
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.Pp
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The asynchronous I/O control buffer
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.Fa iocb
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should be zeroed before the
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.Fn aio_read
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call to avoid passing bogus context information to the kernel.
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.Pp
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Modifications of the Asynchronous I/O Control Block structure or the
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buffer contents after the request has been enqueued, but before the
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request has completed, are not allowed.
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.Pp
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If the file offset in
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.Fa iocb->aio_offset
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is past the offset maximum for
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.Fa iocb->aio_fildes ,
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no I/O will occur.
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.Sh RETURN VALUES
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.Rv -std aio_read
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.Sh DIAGNOSTICS
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None.
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.Sh ERRORS
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The
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.Fn aio_read
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The request was not queued because of system resource limitations.
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.It Bq Er ENOSYS
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The
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.Fn aio_read
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call is not supported.
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.El
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.Pp
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The following conditions may be synchronously detected when the
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.Fn aio_read
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call is made, or asynchronously, at any time thereafter. If they
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are detected at call time,
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.Fn aio_read
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returns -1 and sets
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.Va errno
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appropriately; otherwise the
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.Fn aio_return
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function must be called, and will return -1, and
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.Fn aio_error
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must be called to determine the actual calue that would have been
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returned in
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.Va errno .
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.Pp
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.Bl -tag -width Er
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.It Bq Er EBADF
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.Fa iocb->aio_fildes
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is invalid.
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.It Bq Er EINVAL
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The offset
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.Fa iocb->aio_offset
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is not valid, the priority specified by
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.Fa iocb->aio_reqprio
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is not a valid priority, or the number of bytes specified by
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.Fa iocb->aio_nbytes
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is not valid.
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.It Bq Er EOVERFLOW
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The file is a regular file,
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.Fa iocb->aio_nbytes
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is greater than zero, the starting offset in
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.Fa iocb->aio_offset
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is before the end of the file, but is at or beyond the
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.Fa iocb->aio_fildes
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offset maximum.
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.El
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.Pp
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If the request is successfully enqueued, but subsequently cancelled
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or an error occurs, the value returned by the
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.Fn aio_return
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function is per the
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.Xr read 2
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call, and the value returned by the
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.Fn aio_error
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function is either one of the error returns from the
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.Xr read 2
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call, or one of:
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.Bl -tag -width Er
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.It Bq Er EBADF
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.Fa iocb->aio_fildes
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is invalid for reading.
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.It Bq Er ECANCELED
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The request was explicitly cancelled via a call to
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.Fn aio_cancel .
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.It Bq Er EINVAL
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The offset
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.Fa iocb->aio_offset
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would be invalid.
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.El
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.Sh STANDARDS
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The
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.Fn aio_read
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call is expected to conform to the
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.St -p1003.2
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standard.
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.Sh HISTORY
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The
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.Nm
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function first appeared in
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.Fx 3.0 .
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.Sh AUTHORS
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This
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manual page was written by
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.An Terry Lambert Aq terry@whistle.com .
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.Sh BUGS
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The value of
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.Fa iocb->aio_offset
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is ignored. Invalid information in
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.Fa iocb->_aiocb_private
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may confuse the kernel.
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