/* if valid callback is passed as argument, fd event polling will be done by user
all file descriptors and events will be passed to user in this callback */
/* if callback is set to NULL libmemif will handle fd event polling */
/* if valid callback is passed as argument, fd event polling will be done by user
all file descriptors and events will be passed to user in this callback */
/* if callback is set to NULL libmemif will handle fd event polling */