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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.
84 .Fa iocb->aio_sigevent
85 structure can be used to request notification of the operation's
86 completion as described in
89 The Asynchronous I/O Control Block structure pointed to by
91 and the buffer that the
93 member of that structure references must remain valid until the
94 operation has completed.
96 The asynchronous I/O control buffer
98 should be zeroed before the
100 call to avoid passing bogus context information to the kernel.
102 Modifications of the Asynchronous I/O Control Block structure or the
103 buffer contents are not allowed while the request is queued.
105 If the file offset in
107 is past the offset maximum for
108 .Fa iocb->aio_fildes ,
117 system call will fail if:
120 The request was not queued because of system resource limitations.
122 The asynchronous notification method in
123 .Fa iocb->aio_sigevent.sigev_notify
124 is invalid or not supported.
126 Asynchronous read operations on the file descriptor
128 are unsafe and unsafe asynchronous I/O operations are disabled.
131 The following conditions may be synchronously detected when the
133 system call is made, or asynchronously, at any time thereafter.
135 are detected at call time,
139 appropriately; otherwise the
141 system call must be called, and will return -1, and
143 must be called to determine the actual value that would have been
155 is not valid, the priority specified by
156 .Fa iocb->aio_reqprio
157 is not a valid priority, or the number of bytes specified by
161 The file is a regular file,
163 is greater than zero, the starting offset in
165 is before the end of the file, but is at or beyond the
170 If the request is successfully enqueued, but subsequently cancelled
171 or an error occurs, the value returned by the
173 system call is per the
175 system call, and the value returned by the
177 system call is either one of the error returns from the
179 system call, or one of:
185 is invalid for reading.
187 The request was explicitly cancelled via a call to
199 .Xr aio_waitcomplete 2 ,
207 system call is expected to conform to the
213 system call first appeared in
217 manual page was written by
218 .An Terry Lambert Aq Mt terry@whistle.com .
220 Invalid information in
221 .Fa iocb->_aiocb_private
222 may confuse the kernel.