[PATCH 2/2] nilfs2: do not update mtime of renamed directory that is not moved

[Ryusuke Konishi <konishi.ryusuke@gmail.com>]

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 39fe7557b4d6 ("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.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
---
 fs/nilfs2/namei.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/fs/nilfs2/namei.c b/fs/nilfs2/namei.c
index e02fae6757f1..953fbd5f0851 100644
--- a/fs/nilfs2/namei.c
+++ b/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,
@@ -412,7 +413,7 @@ 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);
@@ -420,7 +421,7 @@ static int nilfs_rename(struct mnt_idmap *idmap,
 		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);
-- 
2.43.0