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AIO_READ(2)		    BSD	System Calls Manual		   AIO_READ(2)

     aio_read, aio_readv -- asynchronous read from a file (REALTIME)

     Standard C	Library	(libc, -lc)

     #include <aio.h>

     aio_read(struct aiocb *iocb);

     #include <sys/uio.h>

     aio_readv(struct aiocb *iocb);

     The aio_read() and	aio_readv() system calls allow the calling process to
     read from the descriptor iocb-_aio_fildes beginning at the	offset
     iocb-_aio_offset.	aio_read() will	read iocb-_aio_nbytes from the buffer
     pointed to	by iocb-_aio_buf, whereas aio_readv() reads the	data into the
     iocb-_aio_iovcnt buffers specified	by the members of the iocb-_aio_iov
     array.  Both syscalls return immediately after the	read request has been
     enqueued to the descriptor; the read may or may not have completed	at the
     time the call returns.

     For aio_readv() the iovec structure is defined in readv(2).

     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 argument is ignored by the aio_read() and
     aio_readv() system	calls.

     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 en-
     queued 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 iocb-_aio_sigevent structure can be used to request notification of
     the operation's completion	as described in	aio(4).

     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.

     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 buf-
     fer contents are not allowed while	the request is queued.

     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() and	aio_readv() functions return the value 0 if success-
     ful; otherwise the	value -1 is returned and the global variable errno is
     set to indicate the error.


     The aio_read() and	aio_readv() system calls will fail if:

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

     [EFAULT]		Part of	aio_iov	points outside the process's allocated
			address	space.

     [EINVAL]		The asynchronous notification method in
			iocb-_aio_sigevent.sigev_notify	is invalid or not sup-

     [EOPNOTSUPP]	Asynchronous read operations on	the file descriptor
			iocb-_aio_fildes are unsafe and	unsafe asynchronous
			I/O operations are disabled.

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

     [EBADF]		The iocb-_aio_fildes argument 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() system call is per
     the read(2) system	call, and the value returned by	the aio_error()	system
     call is either one	of the error returns from the read(2) system call, or
     one of:

     [EBADF]		The iocb-_aio_fildes argument is invalid for reading.

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

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

     aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2),
     aio_waitcomplete(2), aio_write(2),	sigevent(3), siginfo(3), aio(4)

     The aio_read() system call	is expected to conform to the IEEE Std 1003.1
     ("POSIX.1") standard.  The	aio_readv() system call	is a FreeBSD exten-
     sion, and should not be used in portable code.

     The aio_read() system call	first appeared in FreeBSD 3.0.	The
     aio_readv() system	call first appeared in FreeBSD 13.0.

     This manual page was written by Terry Lambert <>.

     Invalid information in iocb-__aiocb_private may confuse the kernel.

BSD				January	2, 2021				   BSD


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