Re: [PATCH v2 08/92] fs: new helper: simple_rename_timestamp

[Al Viro]

On Wed, Jul 05, 2023 at 02:58:11PM -0400, Jeff Layton wrote:

> + * POSIX mandates that the old and new parent directories have their ctime and
> + * mtime updated, and that inodes of @old_dentry and @new_dentry (if any), have
> + * their ctime updated.

APPLICATION USAGE
Some implementations mark for update the last file status change timestamp
of renamed files and some do not. Applications which make use of the
last file status change timestamp may behave differently with respect
to renamed files unless they are designed to allow for either behavior.

So for children POSIX permits rather than mandates.  Doesn't really matter;
Linux behaviour had been to touch ctime on children since way back, if
not since the very beginning.