block: treat REQ_FUA and REQ_PREFLUSH as synchronous

Instead of requiring everyone to specify the REQ_SYNC flag aѕ well.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/blk_types.h

@@ -216,9 +216,15 @@ static inline bool op_is_write(unsigned int op)
 	return (op & 1);
 }
 
+/*
+ * Reads are always treated as synchronous, as are requests with the FUA or
+ * PREFLUSH flag.  Other operations may be marked as synchronous using the
+ * REQ_SYNC flag.
+ */
 static inline bool op_is_sync(unsigned int op)
 {
-	return (op & REQ_OP_MASK) == REQ_OP_READ || (op & REQ_SYNC);
+	return (op & REQ_OP_MASK) == REQ_OP_READ ||
+		(op & (REQ_SYNC | REQ_FUA | REQ_PREFLUSH));
 }
 
 typedef unsigned int blk_qc_t;

include/linux/fs.h

@@ -199,9 +199,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 #define READ_SYNC		0
 #define WRITE_SYNC		(REQ_SYNC | REQ_NOIDLE)
 #define WRITE_ODIRECT		REQ_SYNC
-#define WRITE_FLUSH		(REQ_SYNC | REQ_NOIDLE | REQ_PREFLUSH)
-#define WRITE_FUA		(REQ_SYNC | REQ_NOIDLE | REQ_FUA)
-#define WRITE_FLUSH_FUA		(REQ_SYNC | REQ_NOIDLE | REQ_PREFLUSH | REQ_FUA)
+#define WRITE_FLUSH		(REQ_NOIDLE | REQ_PREFLUSH)
+#define WRITE_FUA		(REQ_NOIDLE | REQ_FUA)
+#define WRITE_FLUSH_FUA		(REQ_NOIDLE | REQ_PREFLUSH | REQ_FUA)
 
 /*
  * Attribute flags.  These should be or-ed together to figure out what