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

NAME
     aio_read -- asynchronous read from a file (REALTIME)

LIBRARY
     Standard C Library (libc, -lc)

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 descrip-tor; descriptor;
     tor; 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 with-out without
     out 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 com-pleted. completed.
     pleted.  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.

DIAGNOSTICS
     None.

ERRORS
     The aio_read() system call will fail if:

     [EAGAIN]           Because of system resource limitations, the request was not queued.

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

     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.  It will return -1;
     aio_error() must then 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
     aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2), aio_write(2), aio(4)

STANDARDS
     The aio_read() system call is expected to conform to the IEEE Std 1003.1 (``POSIX.1'') standard.

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

AUTHORS
     This manual page was written by Terry Lambert <terry@whistle.com>.

BUGS
     Invalid information in aiocbp->_aiocb_private may confuse the kernel.

BSD                            November 17, 1998                           BSD

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