1 .\" Copyright (c) 1998 Terry Lambert
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
13 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 .\" $FreeBSD: src/lib/libc/sys/aio_read.2,v 1.6.2.5 2002/12/29 16:35:34 schweikh Exp $
26 .\" $DragonFly: src/lib/libc/sys/aio_read.2,v 1.3 2008/05/02 02:05:04 swildner Exp $
33 .Nd asynchronous read from a file (REALTIME)
40 .Fn aio_read "struct aiocb *iocb"
44 function allows the calling process to read
48 beginning at the offset
50 into the buffer pointed to by
52 The call returns immediately after the read request has
53 been enqueued to the descriptor; the read may or may not have
54 completed at the time the call returns.
56 If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it,
57 then the enqueued operation is submitted at a priority equal to that
58 of the calling process minus
59 .Fa iocb->aio_reqprio .
62 .Fa iocb->aio_lio_opcode
69 pointer may be subsequently used as an argument to
73 in order to determine return or error status for the enqueued operation
74 while it is in progress.
76 If the request could not be enqueued (generally due to invalid arguments),
77 then the call returns without having enqueued the request.
79 If the request is successfully enqueued, the value of
81 can be modified during the request as context, so this value must
82 not be referenced after the request is enqueued.
84 The Asynchronous I/O Control Block structure pointed to by
86 and the buffer that the
88 member of that structure references must remain valid until the
89 operation has completed. For this reason, use of auto (stack) variables
90 for these objects is discouraged.
92 The asynchronous I/O control buffer
94 should be zeroed before the
96 call to avoid passing bogus context information to the kernel.
98 Modifications of the Asynchronous I/O Control Block structure or the
99 buffer contents after the request has been enqueued, but before the
100 request has completed, are not allowed.
102 If the file offset in
104 is past the offset maximum for
105 .Fa iocb->aio_fildes ,
114 function will fail if:
117 The request was not queued because of system resource limitations.
121 call is not supported.
124 The following conditions may be synchronously detected when the
126 call is made, or asynchronously, at any time thereafter. If they
127 are detected at call time,
131 appropriately; otherwise the
133 function must be called, and will return -1, and
135 must be called to determine the actual value that would have been
145 is not valid, the priority specified by
146 .Fa iocb->aio_reqprio
147 is not a valid priority, or the number of bytes specified by
151 The file is a regular file,
153 is greater than zero, the starting offset in
155 is before the end of the file, but is at or beyond the
160 If the request is successfully enqueued, but subsequently cancelled
161 or an error occurs, the value returned by the
165 call, and the value returned by the
167 function is either one of the error returns from the
173 is invalid for reading.
175 The request was explicitly cancelled via a call to
185 call is expected to conform to the
191 function first appeared in
195 manual page was written by
196 .An Terry Lambert Aq terry@whistle.com .
200 is ignored. Invalid information in
201 .Fa iocb->_aiocb_private
202 may confuse the kernel.