AIOREAD(2)                 BSD System Calls Manual                AIOREAD(2)

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

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##include <>

     int
     aioread(struct aiocb *iocb);

DESCRIPTION
     The aioread() system call allows the calling process to read
     iocb->aionbytes from the descriptor iocb->aiofildes beginning at the
     offset iocb->aiooffset into the buffer pointed to by iocb->aiobuf.  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 POSIXPRIORITIZEDIO 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->aioreqprio.

     The iocb->aiolioopcode argument is ignored by the aioread() system
     call.

     The iocb pointer may be subsequently used as an argument to aioreturn()
     and aioerror() 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->aiooffset
     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 iocb and the
     buffer that the iocb->aiobuf 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
     aioread() 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->aiooffset is past the offset maximum  for
     iocb->aiofildes, no I/O will occur.

RETURN VALUES
     The aioread() 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.

ERORS
     The aioread() system call will fail if:

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

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

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

     [EBADF]            The iocb->aiofildes argument is invalid.

     [EINVAL]           The offset iocb->aiooffset is not valid, the priority
                        specified by iocb->aioreqprio is not a valid prior-
                        ity, or the number of bytes specified by
                        iocb->aionbytes is not valid.

     [EOVERFLOW]        The file is a regular file, iocb->aionbytes is
                        greater than zero, the starting offset in
                        iocb->aiooffset is before the end of the file, but is
                        at or beyond the iocb->aiofildes offset maximum.

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

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

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

     [EINVAL]           The offset iocb->aiooffset would be invalid.

SEE ALSO
     aiocancel(2), aioerror(2), aioreturn(2), aiosuspend(2), aiowrite(2),
     aio(4)

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

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

AUTHORS
     This manual page was written by Terry Lambert .

BUGS
     Invalid information in iocb->aiocbprivate may confuse the kernel.

BSD                            November 17, 1998                           BSD