ext2: Do not update mtime of a moved directory

One of our users is complaining that his backup tool is upset on ext2
(while it's happy on ext3, xfs, ...) because of the mtime change.

The problem is:

    mkdir foo
    mkdir bar
    mkdir foo/a

Now under ext2:
    mv foo/a foo/b

changes mtime of 'foo/a' (foo/b after the move).  That does not really
make sense and it does not happen under any other filesystem I've seen.

More complicated is:
    mv foo/a bar/a

This changes mtime of foo/a (bar/a after the move) and it makes some
sense since we had to update parent directory pointer of foo/a.  But
again, no other filesystem does this.  So after some thoughts I'd vote
for consistency and change ext2 to behave the same as other filesystems.

Do not update mtime of a moved directory.  Specs don't say anything
about it (neither that it should, nor that it should not be updated) and
other common filesystems (ext3, ext4, xfs, reiserfs, fat, ...) don't do
it.  So let's become more consistent.

Spotted by ronny.pretzsch@dfs.de, initial fix by Jörn Engel.

Reported-by: <ronny.pretzsch@dfs.de>
Cc: <hare@suse.de>
Cc: Jörn Engel <joern@logfs.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ext2/dir.c

@@ -450,7 +450,7 @@ ino_t ext2_inode_by_name(struct inode *dir, struct qstr *child)
 
 /* Releases the page */
 void ext2_set_link(struct inode *dir, struct ext2_dir_entry_2 *de,
-			struct page *page, struct inode *inode)
+		   struct page *page, struct inode *inode, int update_times)
 {
 	loff_t pos = page_offset(page) +
 			(char *) de - (char *) page_address(page);
@@ -465,6 +465,7 @@ void ext2_set_link(struct inode *dir, struct ext2_dir_entry_2 *de,
 	ext2_set_de_type(de, inode);
 	err = ext2_commit_chunk(page, pos, len);
 	ext2_put_page(page);
+	if (update_times)
 		dir->i_mtime = dir->i_ctime = CURRENT_TIME_SEC;
 	EXT2_I(dir)->i_flags &= ~EXT2_BTREE_FL;
 	mark_inode_dirty(dir);

fs/ext2/ext2.h

@@ -111,7 +111,7 @@ extern struct ext2_dir_entry_2 * ext2_find_entry (struct inode *,struct qstr *,
 extern int ext2_delete_entry (struct ext2_dir_entry_2 *, struct page *);
 extern int ext2_empty_dir (struct inode *);
 extern struct ext2_dir_entry_2 * ext2_dotdot (struct inode *, struct page **);
-extern void ext2_set_link(struct inode *, struct ext2_dir_entry_2 *, struct page *, struct inode *);
+extern void ext2_set_link(struct inode *, struct ext2_dir_entry_2 *, struct page *, struct inode *, int);
 
 /* ialloc.c */
 extern struct inode * ext2_new_inode (struct inode *, int);

fs/ext2/namei.c

@@ -320,7 +320,7 @@ static int ext2_rename (struct inode * old_dir, struct dentry * old_dentry,
 		if (!new_de)
 			goto out_dir;
 		inode_inc_link_count(old_inode);
-		ext2_set_link(new_dir, new_de, new_page, old_inode);
+		ext2_set_link(new_dir, new_de, new_page, old_inode, 1);
 		new_inode->i_ctime = CURRENT_TIME_SEC;
 		if (dir_de)
 			drop_nlink(new_inode);
@@ -352,7 +352,8 @@ static int ext2_rename (struct inode * old_dir, struct dentry * old_dentry,
 	inode_dec_link_count(old_inode);
 
 	if (dir_de) {
-		ext2_set_link(old_inode, dir_de, dir_page, new_dir);
+		if (old_dir != new_dir)
+			ext2_set_link(old_inode, dir_de, dir_page, new_dir, 0);
 		inode_dec_link_count(old_dir);
 	}
 	return 0;