How to recognize synchronous write requests

Hi all, As much as I know, type of an IO request can be realized by "DATA_DIR" macro,but I wanted to know if it is possible to distinguish a read or write is synchronous or asychronous. I'm also using "blktrace" to extract requests dispatching to disk. blktrace, determines synchrnous writes as "ws" and asynchronous writes as "w". Regards, -- Amirali Shambayati Bachelor Student Computer Engineering Department Sharif University of Technology Tehran, Iran