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AIO_READ(3)                Library Functions Manual                AIO_READ(3)

NAME
     aio_read - asynchronous read from a file (REALTIME)

LIBRARY
     POSIX Real-time Library (librt, -lrt)

SYNOPSIS
     #include <aio.h>

     int
     aio_read(struct aiocb *aiocbp);

DESCRIPTION
     The aio_read() system call allows the calling process to read
     aiocbp->aio_nbytes from the descriptor aiocbp->aio_fildes beginning at
     the offset aiocbp->aio_offset into the buffer pointed to by
     aiocbp->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 returns.

     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 aiocbp->aio_reqprio.

     The aiocbp->aio_lio_opcode argument is ignored by the aio_read() system
     call.

     The aiocbp 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
     arguments), then the call returns without having enqueued the request.

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

RESTRICTIONS
     The Asynchronous I/O Control Block structure pointed to by aiocbp and the
     buffer that the aiocbp->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 aiocbp 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 aiocbp->aio_offset is past the offset maximum for
     aiocbp->aio_fildes, no I/O will occur.

RETURN VALUES
     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
     error.

ERRORS
     The aio_read() system call will fail if:

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

     The following conditions may be synchronously detected when the
     aio_read() system 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() 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 aiocbp->aio_fildes argument is invalid.

     [EINVAL]           The offset aiocbp->aio_offset is not valid, the
                        priority specified by aiocbp->aio_reqprio is not a
                        valid priority, or the number of bytes specified by
                        aiocbp->aio_nbytes is not valid.

     [EOVERFLOW]        The file is a regular file, aiocbp->aio_nbytes is
                        greater than zero, the starting offset in
                        aiocbp->aio_offset is before the end of the file, but
                        is at or beyond the aiocbp->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 aiocbp->aio_fildes argument is invalid for
                        reading.

     [ECANCELED]        The request was explicitly cancelled via a call to
                        aio_cancel().

     [EINVAL]           The offset aiocbp->aio_offset would be invalid.

SEE ALSO
     siginfo(2), aio(3)

STANDARDS
     The aio_read() system call is expected to conform to the IEEE Std
     1003.1-2001 ("POSIX.1") standard.

HISTORY
     The aio_read() system call first appeared in NetBSD 5.0.

NetBSD 10.99                     May 17, 2010                     NetBSD 10.99