how to convert FilterGetMessage function from c to c#

[DllImport("FltLib", CallingConvention = CallingConvention.Winapi, CharSet = CharSet.Auto)]
           private static extern int <small>FilterGetMessage</small>(
                IntPtr hPort,
               IntPtr lpMessageBuffer,
               int dwMessageBufferSize,
               ref OVERLAPPED lpOverlapped);

public struct OVERLAPPED {
    public UIntPtr Internal;
    public UIntPtr InternalHigh;

        public uint Offset;
        public uint OffsetHigh;
        public IntPtr Pointer;

    public IntPtr hEvent;
}
   OVERLAPPED povlp;
  povlp.Internal = UIntPtr.Zero;
             povlp.InternalHigh = UIntPtr.Zero;
             povlp.Offset = 0;
             povlp.OffsetHigh = 0;
             povlp.Pointer = IntPtr.Zero;
             povlp.hEvent = IntPtr.Zero;
             headerSize = Marshal.SizeOf(msg.MessageHeader);

                 msgsize += headerSize;
                 status = FilterGetMessage(
                     portPtr,
                     buf,
                     msgsize,
                     ref povlp);