[RFC PATCH v4 9/9] ovl: implement containerized syncfs for overlayfs

[Chengguang Xu <cgxu519@mykernel.net>]

Now overlayfs can only sync dirty inode during syncfs,
so remove unnecessary sync_filesystem() on upper file
system.

Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
---
 fs/overlayfs/super.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 982b3954b47c..58507f1cd583 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -15,6 +15,8 @@
 #include <linux/seq_file.h>
 #include <linux/posix_acl_xattr.h>
 #include <linux/exportfs.h>
+#include <linux/blkdev.h>
+#include <linux/writeback.h>
 #include "overlayfs.h"
 
 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
@@ -270,8 +272,7 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
 	 * Not called for sync(2) call or an emergency sync (SB_I_SKIP_SYNC).
 	 * All the super blocks will be iterated, including upper_sb.
 	 *
-	 * If this is a syncfs(2) call, then we do need to call
-	 * sync_filesystem() on upper_sb, but enough if we do it when being
+	 * if this is a syncfs(2) call, it will be enough we do it when being
 	 * called with wait == 1.
 	 */
 	if (!wait)
@@ -280,7 +281,11 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
 	upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
 
 	down_read(&upper_sb->s_umount);
-	ret = sync_filesystem(upper_sb);
+	wait_sb_inodes(upper_sb);
+	if (upper_sb->s_op->sync_fs)
+		ret = upper_sb->s_op->sync_fs(upper_sb, wait);
+	if (!ret)
+		ret = sync_blockdev(upper_sb->s_bdev);
 	up_read(&upper_sb->s_umount);
 
 	return ret;
-- 
2.26.2