Man page for aio_read(2).

Submitted by:	Terry Lambert <terry@whistle.com> on the -doc lists.

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