nilfs2: do not update mtime of renamed directory that is not moved

A minor issue with nilfs_rename, originating from an old ext2
implementation, is that the mtime is updated even if the rename target is
a directory and it is renamed within the same directory, rather than moved
to a different directory.

In this case, the child directory being renamed does not change in any
way, so changing its mtime is unnecessary according to the specification,
and can unnecessarily confuse backup tools.

In ext2, this issue was fixed by commit 39fe755 ("ext2: Do not update
mtime of a moved directory") and a few subsequent fixes, but it remained
in nilfs2.

Fix this issue by not calling nilfs_set_link(), which rewrites the inode
number of the directory entry that refers to the parent directory, when
the move target is a directory and the source and destination are the same
directory.

Here, the directory to be moved only needs to be read if the inode number
of the parent directory is rewritten with nilfs_set_link, so also adjust
the execution conditions of the preparation work to avoid unnecessary
directory reads.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ryusuke Konishi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: konis

fs/nilfs2/namei.c

@@ -370,6 +370,7 @@ static int nilfs_rename(struct mnt_idmap *idmap,
 	struct folio *old_folio;
 	struct nilfs_dir_entry *old_de;
 	struct nilfs_transaction_info ti;
+	bool old_is_dir = S_ISDIR(old_inode->i_mode);
 	int err;
 
 	if (flags & ~RENAME_NOREPLACE)
@@ -385,7 +386,7 @@ static int nilfs_rename(struct mnt_idmap *idmap,
 		goto out;
 	}
 
-	if (S_ISDIR(old_inode->i_mode)) {
+	if (old_is_dir && old_dir != new_dir) {
 		err = -EIO;
 		dir_de = nilfs_dotdot(old_inode, &dir_folio);
 		if (!dir_de)
@@ -397,7 +398,7 @@ static int nilfs_rename(struct mnt_idmap *idmap,
 		struct nilfs_dir_entry *new_de;
 
 		err = -ENOTEMPTY;
-		if (dir_de && !nilfs_empty_dir(new_inode))
+		if (old_is_dir && !nilfs_empty_dir(new_inode))
 			goto out_dir;
 
 		new_de = nilfs_find_entry(new_dir, &new_dentry->d_name,
@@ -412,15 +413,15 @@ static int nilfs_rename(struct mnt_idmap *idmap,
 			goto out_dir;
 		nilfs_mark_inode_dirty(new_dir);
 		inode_set_ctime_current(new_inode);
-		if (dir_de)
+		if (old_is_dir)
 			drop_nlink(new_inode);
 		drop_nlink(new_inode);
 		nilfs_mark_inode_dirty(new_inode);
 	} else {
 		err = nilfs_add_link(new_dentry, old_inode);
 		if (err)
 			goto out_dir;
-		if (dir_de) {
+		if (old_is_dir) {
 			inc_nlink(new_dir);
 			nilfs_mark_inode_dirty(new_dir);
 		}
@@ -434,9 +435,10 @@ static int nilfs_rename(struct mnt_idmap *idmap,
 
 	err = nilfs_delete_entry(old_de, old_folio);
 	if (likely(!err)) {
-		if (dir_de) {
-			err = nilfs_set_link(old_inode, dir_de, dir_folio,
-					     new_dir);
+		if (old_is_dir) {
+			if (old_dir != new_dir)
+				err = nilfs_set_link(old_inode, dir_de,
+						     dir_folio, new_dir);
 			drop_nlink(old_dir);
 		}
 		nilfs_mark_inode_dirty(old_dir);