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aio_read - asynchronous read from a file (REALTIME)

 

NAME

      aio_read - asynchronous read from a file (REALTIME)
 

LIBRARY

      Standard C Library (libc, -lc)
 

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

Sections

Based on BSD UNIX
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