ocfs2: Flush drive's caches on fdatasync

When 'barrier' mount option is specified, we have to issue a cache flush
during fdatasync(2). We have to do this even if inode doesn't have
I_DIRTY_DATASYNC set because we still have to get written *data* to disk so
that they are not lost in case of crash.
Acked-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Singed-off-by: NTao Ma <tao.ma@oracle.com>

fs/ocfs2/file.c

@@ -36,6 +36,7 @@
 #include <linux/writeback.h>
 #include <linux/falloc.h>
 #include <linux/quotaops.h>
+#include <linux/blkdev.h>
 
 #define MLOG_MASK_PREFIX ML_INODE
 #include <cluster/masklog.h>
@@ -190,8 +191,16 @@ static int ocfs2_sync_file(struct file *file, int datasync)
 	if (err)
 		goto bail;
 
-	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
+	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC)) {
+		/*
+		 * We still have to flush drive's caches to get data to the
+		 * platter
+		 */
+		if (osb->s_mount_opt & OCFS2_MOUNT_BARRIER)
+			blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL,
+					   NULL, BLKDEV_IFL_WAIT);
 		goto bail;
+	}
 
 	journal = osb->journal->j_journal;
 	err = jbd2_journal_force_commit(journal);