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32 .Nd asynchronous read from a file (REALTIME)
38 .Fn aio_read "struct aiocb *iocb"
42 system call allows the calling process to read
46 beginning at the offset
48 into the buffer pointed to by
50 The call returns immediately after the read request has
51 been enqueued to the descriptor; the read may or may not have
52 completed at the time the call returns.
54 If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it,
55 then the enqueued operation is submitted at a priority equal to that
56 of the calling process minus
57 .Fa iocb->aio_reqprio .
60 .Fa iocb->aio_lio_opcode
68 pointer may be subsequently used as an argument to
72 in order to determine return or error status for the enqueued operation
73 while it is in progress.
75 If the request could not be enqueued (generally due to invalid arguments),
76 then the call returns without having enqueued the request.
78 If the request is successfully enqueued, the value of
80 can be modified during the request as context, so this value must
81 not be referenced after the request is enqueued.
83 The Asynchronous I/O Control Block structure pointed to by
85 and the buffer that the
87 member of that structure references must remain valid until the
88 operation has completed.
89 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 system call will fail if:
117 The request was not queued because of system resource limitations.
121 system call is not supported.
124 The following conditions may be synchronously detected when the
126 system call is made, or asynchronously, at any time thereafter.
128 are detected at call time,
132 appropriately; otherwise the
134 system call must be called, and will return -1, and
136 must be called to determine the actual value that would have been
148 is not valid, the priority specified by
149 .Fa iocb->aio_reqprio
150 is not a valid priority, or the number of bytes specified by
154 The file is a regular file,
156 is greater than zero, the starting offset in
158 is before the end of the file, but is at or beyond the
163 If the request is successfully enqueued, but subsequently cancelled
164 or an error occurs, the value returned by the
166 system call is per the
168 system call, and the value returned by the
170 system call is either one of the error returns from the
172 system call, or one of:
178 is invalid for reading.
180 The request was explicitly cancelled via a call to
192 .Xr aio_waitcomplete 2 ,
199 system call is expected to conform to the
205 system call first appeared in
209 manual page was written by
210 .An Terry Lambert Aq terry@whistle.com .
212 Invalid information in
213 .Fa iocb->_aiocb_private
214 may confuse the kernel.