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a52cb4c480
Reviewed by: jhb Discussed with: asomers Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D43448
289 lines
7.0 KiB
Groff
289 lines
7.0 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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.Dd February 1, 2024
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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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.Nm aio_read2 ,
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.Nm aio_readv
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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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.In aio.h
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.Ft int
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.Fn aio_read "struct aiocb *iocb"
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.Ft int
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.Fn aio_read2 "struct aiocb *iocb" "int flags"
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.In sys/uio.h
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.Ft int
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.Fn aio_readv "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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.Fn aio_read2
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and
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.Fn aio_readv
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system calls allow the calling process to read
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from the descriptor
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.Fa iocb->aio_fildes .
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The syscalls return 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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For the
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.Fn aio_read
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and
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.Fn aio_readv
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calls, the read begins at the offset
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.Fa iocb->aio_offset .
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.Pp
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The
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.Fn aio_read
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call will read
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.Fa iocb->aio_nbytes
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into the buffer pointed to by
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.Fa iocb->aio_buf ,
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whereas
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.Fn aio_readv
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reads the data into the
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.Fa iocb->aio_iovcnt
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buffers specified by the members of the
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.Fa iocb->aio_iov
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array.
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For
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.Fn aio_readv
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the
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.Fa iovec
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structure is defined in
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.Xr readv 2 .
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.Pp
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The
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.Fn aio_read2
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call takes the
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.Fa flags
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argument.
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If
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.Fa flags
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is passed as zero, the call behaves identically to
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.Fn aio_read .
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The following flags can be specified by logical or:
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.Bl -tag -width AIO_OP2_VECTORED
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.It AIO_OP2_FOFFSET
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The read occurs at the file descriptor offset,
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which is advanced by the operation as done by the
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.Xr read 2
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syscall.
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The
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.Fa iocb->aio_offset
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field is ignored.
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.It AIO_OP2_VECTORED
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Similar to
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.Fn aio_readv ,
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the read buffers are specified by the
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.Fa aiocb->aio_iov
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array.
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.El
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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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.Pp
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The
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.Fa iocb->aio_sigevent
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structure can be used to request notification of the operation's
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completion as described in
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.Xr aio 4 .
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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.
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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 system
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calls 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 are not allowed while the request is queued.
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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 aio_read2 aio_readv
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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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.Fn aio_read2 ,
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and
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.Fn aio_readv
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system calls 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 EFAULT
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Part of
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.Fa aio_iov
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points outside the process's allocated address space.
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.It Bq Er EINVAL
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The asynchronous notification method in
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.Fa iocb->aio_sigevent.sigev_notify
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is invalid or not supported.
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.It Bq Er EOPNOTSUPP
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Asynchronous read operations on the file descriptor
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.Fa iocb->aio_fildes
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are unsafe and unsafe asynchronous I/O operations are disabled.
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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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or
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.Fn aio_readv
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system call is made, or asynchronously, at any time thereafter.
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If they
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are detected at call time,
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The calls return -1 and set
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.Va errno
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appropriately; otherwise the
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.Fn aio_return
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system call 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 value that would have been
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returned in
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.Va errno .
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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 iocb->aio_fildes
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argument
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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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system call is per the
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.Xr read 2
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system call, and the value returned by the
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.Fn aio_error
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system call is either one of the error returns from the
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.Xr read 2
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system call, or one of:
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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 iocb->aio_fildes
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argument
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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 SEE ALSO
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.Xr aio_cancel 2 ,
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.Xr aio_error 2 ,
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.Xr aio_return 2 ,
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.Xr aio_suspend 2 ,
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.Xr aio_waitcomplete 2 ,
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.Xr aio_write 2 ,
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.Xr sigevent 3 ,
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.Xr siginfo 3 ,
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.Xr aio 4
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.Sh STANDARDS
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The
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.Fn aio_read
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system call is expected to conform to the
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.St -p1003.1
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standard.
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The
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.Fn aio_read2
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and
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.Fn aio_readv
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system calls are FreeBSD extensions,
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and should not be used in portable code.
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.Sh HISTORY
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The
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.Fn aio_read
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system call first appeared in
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.Fx 3.0 .
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The
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.Fn aio_readv
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system call first appeared in
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.Fx 13.0 .
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The
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.Fn aio_read2
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system call first appeared in
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.Fx 14.1 .
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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 Mt terry@whistle.com .
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.Sh BUGS
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Invalid information in
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.Fa iocb->_aiocb_private
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may confuse the kernel.
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