Re: [PATCH 3/6] ovl: reflow ovl_create_or_link()

[Amir Goldstein <amir73il@gmail.com>]

On Fri, Nov 14, 2025 at 11:15 AM Christian Brauner <brauner@kernel.org> wrote:
>
> Reflow the creation routine in preparation of porting it to a guard.
>
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> ---
>  fs/overlayfs/dir.c | 23 +++++++++++++++--------
>  1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index a276eafb5e78..ff30a91e07f8 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -644,14 +644,23 @@ static const struct cred *ovl_setup_cred_for_create(struct dentry *dentry,
>         return override_cred;
>  }
>
> +static int do_ovl_create_or_link(struct dentry *dentry, struct inode *inode,
> +                                struct ovl_cattr *attr)

Trying to avert the bikesheding over do_ovl_ helper name...

> +{
> +       if (!ovl_dentry_is_whiteout(dentry))
> +               return ovl_create_upper(dentry, inode, attr);
> +
> +       return ovl_create_over_whiteout(dentry, inode, attr);
> +}
> +
>  static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
>                               struct ovl_cattr *attr, bool origin)
>  {
>         int err;
> -       const struct cred *new_cred __free(put_cred) = NULL;
>         struct dentry *parent = dentry->d_parent;
>
>         scoped_class(override_creds_ovl, old_cred, dentry->d_sb) {
> +               const struct cred *new_cred __free(put_cred) = NULL;
>                 /*
>                  * When linking a file with copy up origin into a new parent, mark the
>                  * new parent dir "impure".
> @@ -662,7 +671,6 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
>                                 return err;
>                 }
>
> -               if (!attr->hardlink) {
>                 /*
>                  * In the creation cases(create, mkdir, mknod, symlink),
>                  * ovl should transfer current's fs{u,g}id to underlying
> @@ -676,16 +684,15 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
>                  * create a new inode, so just use the ovl mounter's
>                  * fs{u,g}id.
>                  */
> +
> +               if (attr->hardlink)
> +                       return do_ovl_create_or_link(dentry, inode, attr);
> +

^^^ This looks like an optimization (don't setup cred for hardlink).
Is it really an important optimization that is worth complicating the code flow?
What if we just drop the optimization instead?
Would that creak anything?

Thanks,
Amir.