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
31 .Nd asynchronous read from a file (REALTIME)
37 .Fn aio_read "struct aiocb *iocb"
40 .Fn aio_readv "struct aiocb *iocb"
46 system calls allow the calling process to read
49 beginning at the offset
50 .Fa iocb->aio_offset .
54 into the buffer pointed to by
58 reads the data into the
60 buffers specified by the members of the
63 Both syscalls return immediately after the read request has
64 been enqueued to the descriptor; the read may or may not have
65 completed at the time the call returns.
71 structure is defined in
74 If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it,
75 then the enqueued operation is submitted at a priority equal to that
76 of the calling process minus
77 .Fa iocb->aio_reqprio .
80 .Fa iocb->aio_lio_opcode
90 pointer may be subsequently used as an argument to
94 in order to determine return or error status for the enqueued operation
95 while it is in progress.
97 If the request could not be enqueued (generally due to invalid arguments),
98 then the call returns without having enqueued the request.
100 If the request is successfully enqueued, the value of
102 can be modified during the request as context, so this value must
103 not be referenced after the request is enqueued.
106 .Fa iocb->aio_sigevent
107 structure can be used to request notification of the operation's
108 completion as described in
111 The Asynchronous I/O Control Block structure pointed to by
113 and the buffer that the
115 member of that structure references must remain valid until the
116 operation has completed.
118 The asynchronous I/O control buffer
120 should be zeroed before the
122 call to avoid passing bogus context information to the kernel.
124 Modifications of the Asynchronous I/O Control Block structure or the
125 buffer contents are not allowed while the request is queued.
127 If the file offset in
129 is past the offset maximum for
130 .Fa iocb->aio_fildes ,
133 .Rv -std aio_read aio_readv
141 system calls will fail if:
144 The request was not queued because of system resource limitations.
148 points outside the process's allocated address space.
150 The asynchronous notification method in
151 .Fa iocb->aio_sigevent.sigev_notify
152 is invalid or not supported.
154 Asynchronous read operations on the file descriptor
156 are unsafe and unsafe asynchronous I/O operations are disabled.
159 The following conditions may be synchronously detected when the
163 system call is made, or asynchronously, at any time thereafter.
165 are detected at call time,
171 appropriately; otherwise the
173 system call must be called, and will return -1, and
175 must be called to determine the actual value that would have been
187 is not valid, the priority specified by
188 .Fa iocb->aio_reqprio
189 is not a valid priority, or the number of bytes specified by
193 The file is a regular file,
195 is greater than zero, the starting offset in
197 is before the end of the file, but is at or beyond the
202 If the request is successfully enqueued, but subsequently cancelled
203 or an error occurs, the value returned by the
205 system call is per the
207 system call, and the value returned by the
209 system call is either one of the error returns from the
211 system call, or one of:
217 is invalid for reading.
219 The request was explicitly cancelled via a call to
231 .Xr aio_waitcomplete 2 ,
239 system call is expected to conform to the
244 system call is a FreeBSD extension, and should not be used in portable code.
248 system call first appeared in
252 system call first appeared in
256 manual page was written by
257 .An Terry Lambert Aq Mt terry@whistle.com .
259 Invalid information in
260 .Fa iocb->_aiocb_private
261 may confuse the kernel.