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    Command:

    aio_read

    
    
    
    

    SYNOPSIS

         #include <aio.h>
    
         int
         aio_read(struct aiocb *iocb);
    
    
    

    DESCRIPTION

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

    RESTRICTIONS

         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.
    
    
    

    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
         aio_read() system call is made, or asynchronously, at any time there-
         after.  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 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
                            aio_cancel().
    
         [EINVAL]           The offset iocb->aio_offset would be invalid.
    
    
    

    SEE ALSO

         aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2),
         aio_waitcomplete(2), aio_write(2), siginfo(3), 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 iocb->_aiocb_private may confuse the kernel.
    
    
    

    BSD November 17, 1998 BSD

    
    
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