hfsplus: flush disk caches in sync and fsync

Flush the disk cache in fsync and sync to make sure data actually is
on disk on completion of these system calls.  There is a nobarrier
mount option to disable this behaviour.  It's slightly misnamed now
that barrier actually are gone, but it matches the name used by all
major filesystems.

Signed-off-by: Christoph Hellwig <hch@tuxera.com>

fs/hfsplus/hfsplus_fs.h

@@ -156,6 +156,7 @@ struct hfsplus_sb_info {
 #define HFSPLUS_SB_FORCE	2
 #define HFSPLUS_SB_HFSX		3
 #define HFSPLUS_SB_CASEFOLD	4
+#define HFSPLUS_SB_NOBARRIER	5
 
 static inline struct hfsplus_sb_info *HFSPLUS_SB(struct super_block *sb)
 {