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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 request'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.
95 For this reason, use of auto (stack) variables
96 for these objects is discouraged.
98 The asynchronous I/O control buffer
100 should be zeroed before the
102 call to avoid passing bogus context information to the kernel.
104 Modifications of the Asynchronous I/O Control Block structure or the
105 buffer contents after the request has been enqueued, but before the
106 request has completed, are not allowed.
108 If the file offset in
110 is past the offset maximum for
111 .Fa iocb->aio_fildes ,
120 system call will fail if:
123 The request was not queued because of system resource limitations.
125 The asynchronous notification method in
126 .Fa iocb->aio_sigevent.sigev_notify
127 is invalid or not supported.
131 system call is not supported.
134 The following conditions may be synchronously detected when the
136 system call is made, or asynchronously, at any time thereafter.
138 are detected at call time,
142 appropriately; otherwise the
144 system call must be called, and will return -1, and
146 must be called to determine the actual value that would have been
158 is not valid, the priority specified by
159 .Fa iocb->aio_reqprio
160 is not a valid priority, or the number of bytes specified by
164 The file is a regular file,
166 is greater than zero, the starting offset in
168 is before the end of the file, but is at or beyond the
173 If the request is successfully enqueued, but subsequently cancelled
174 or an error occurs, the value returned by the
176 system call is per the
178 system call, and the value returned by the
180 system call is either one of the error returns from the
182 system call, or one of:
188 is invalid for reading.
190 The request was explicitly cancelled via a call to
202 .Xr aio_waitcomplete 2 ,
210 system call is expected to conform to the
216 system call first appeared in
220 manual page was written by
221 .An Terry Lambert Aq terry@whistle.com .
223 Invalid information in
224 .Fa iocb->_aiocb_private
225 may confuse the kernel.