Add barrier fsync test case

Also changes the fsync prep helper to require passing in the actual
flag, not just a boolean for fsync vs fdatasync.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

src/liburing.h

@@ -131,13 +131,12 @@ static inline void io_uring_prep_poll_remove(struct io_uring_sqe *sqe,
 }
 
 static inline void io_uring_prep_fsync(struct io_uring_sqe *sqe, int fd,
-				       int datasync)
+				       unsigned fsync_flags)
 {
 	memset(sqe, 0, sizeof(*sqe));
 	sqe->opcode = IORING_OP_FSYNC;
 	sqe->fd = fd;
-	if (datasync)
-		sqe->fsync_flags = IORING_FSYNC_DATASYNC;
+	sqe->fsync_flags = fsync_flags;
 }
 
 #endif