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AIO_READ(2)		  FreeBSD System Calls Manual		   AIO_READ(2)

     aio_read -- asynchronous read from	a file (REALTIME)

     Standard C	Library	(libc, -lc)

     #include <time.h>
     #include <aio.h>

     aio_read(struct aiocb *iocb);

     The aio_read() function allows the	calling	process	to read
     iocb-_aio_nbytes from the descriptor iocb-_aio_fildes beginning at	the
     offset iocb-_aio_offset into the buffer pointed to	by iocb-_aio_buf.  The
     call returns immediately after the	read request has been enqueued to the
     descriptor; the read may or may not have completed	at the time the	call

     If	_POSIX_PRIORITIZED_IO is defined, and the descriptor supports it, then
     the enqueued operation is submitted at a priority equal to	that of	the
     calling process minus iocb-_aio_reqprio.

     The iocb-_aio_lio_opcode is ignored by the	aio_read() call.

     The iocb pointer may be subsequently used as an argument to aio_return()
     and aio_error() in	order to determine return or error status for the
     enqueued operation	while it is in progress.

     If	the request could not be enqueued (generally due to invalid argu-
     ments), then the call returns without having enqueued the request.

     If	the request is successfully enqueued, the value	of iocb-_aio_offset
     can be modified during the	request	as context, so this value must not be
     referenced	after the request is enqueued.

     The Asynchronous I/O Control Block	structure pointed to by	iocb and the
     buffer that the iocb-_aio_buf member of that structure references must
     remain valid until	the operation has completed.  For this reason, use of
     auto (stack) variables for	these objects is discouraged.

     The asynchronous I/O control buffer iocb should be	zeroed before the
     aio_read()	call to	avoid passing bogus context information	to the kernel.

     Modifications of the Asynchronous I/O Control Block structure or the
     buffer contents after the request has been	enqueued, but before the
     request has completed, are	not allowed.

     If	the file offset	in iocb-_aio_offset is past the	offset maximum	for
     iocb-_aio_fildes, no I/O will occur.

     The aio_read() function returns the value 0 if successful;	otherwise the
     value -1 is returned and the global variable errno	is set to indicate the


     The aio_read() function will fail if:

     [EAGAIN]		The request was	not queued because of system resource

     [ENOSYS]		The aio_read() call is not supported.

     The following conditions may be synchronously detected when the
     aio_read()	call is	made, or asynchronously, at any	time thereafter.  If
     they are detected at call time, aio_read()	returns	-1 and sets errno
     appropriately; otherwise the aio_return() function	must be	called,	and
     will return -1, and aio_error() must be called to determine the actual
     calue that	would have been	returned in errno.

     [EBADF]		iocb-_aio_fildes is invalid.

     [EINVAL]		The offset iocb-_aio_offset is not valid, the priority
			specified by iocb-_aio_reqprio is not a	valid prior-
			ity, or	the number of bytes specified by
			iocb-_aio_nbytes is not	valid.

     [EOVERFLOW]	The file is a regular file, iocb-_aio_nbytes is
			greater	than zero, the starting	offset in
			iocb-_aio_offset is before the end of the file,	but is
			at or beyond the iocb-_aio_fildes offset maximum.

     If	the request is successfully enqueued, but subsequently cancelled or an
     error occurs, the value returned by the aio_return() function is per the
     read(2) call, and the value returned by the aio_error() function is
     either one	of the error returns from the read(2) call, or one of:

     [EBADF]		iocb-_aio_fildes is invalid for	reading.

     [ECANCELED]	The request was	explicitly cancelled via a call	to

     [EINVAL]		The offset iocb-_aio_offset would be invalid.

     The aio_read() call is expected to	conform	to the IEEE Std	1003.2
     (``POSIX.2'') standard.

     The aio_read function first appeared in FreeBSD 3.0.

     This manual page was written by Terry Lambert <>.

     The value of iocb-_aio_offset is ignored.	Invalid	information in
     iocb-__aiocb_private may confuse the kernel.

FreeBSD	11.0		       November	17, 1998		  FreeBSD 11.0


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