Re: [PATCH v6 9/9] ovl: Support mounting case-insensitive enabled layers

[Amir Goldstein]

On Fri, Aug 22, 2025 at 4:17 PM André Almeida <andrealmeid@xxxxxxxxxx> wrote:
>
> Drop the restriction for casefold dentries lookup to enable support for
> case-insensitive layers in overlayfs.
>
> Support case-insensitive layers with the condition that they should be
> uniformly enabled across the stack and (i.e. if the root mount dir has
> casefold enabled, so should all the dirs bellow for every layer).
>
> Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
> Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
> ---
> Changes from v5:
> - Fix mounting layers without casefold flag
> ---
>  fs/overlayfs/namei.c | 17 +++++++++--------
>  fs/overlayfs/util.c  | 10 ++++++----
>  2 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 76d6248b625e7c58e09685e421aef616aadea40a..e93bcc5727bcafdc18a499b47a7609fd41ecaec8 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -239,13 +239,14 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
>         char val;
>
>         /*
> -        * We allow filesystems that are case-folding capable but deny composing
> -        * ovl stack from case-folded directories. If someone has enabled case
> -        * folding on a directory on underlying layer, the warranty of the ovl
> -        * stack is voided.
> +        * We allow filesystems that are case-folding capable as long as the
> +        * layers are consistently enabled in the stack, enabled for every dir
> +        * or disabled in all dirs. If someone has modified case folding on a
> +        * directory on underlying layer, the warranty of the ovl stack is
> +        * voided.
>          */
> -       if (ovl_dentry_casefolded(base)) {
> -               warn = "case folded parent";
> +       if (ofs->casefold != ovl_dentry_casefolded(base)) {
> +               warn = "parent wrong casefold";
>                 err = -ESTALE;
>                 goto out_warn;
>         }
> @@ -259,8 +260,8 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
>                 goto out_err;
>         }
>
> -       if (ovl_dentry_casefolded(this)) {
> -               warn = "case folded child";
> +       if (ofs->casefold != ovl_dentry_casefolded(this)) {
> +               warn = "child wrong casefold";
>                 err = -EREMOTE;
>                 goto out_warn;
>         }
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index a33115e7384c129c543746326642813add63f060..52582b1da52598fbb14866f8c33eb27e36adda36 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -203,6 +203,8 @@ void ovl_dentry_init_flags(struct dentry *dentry, struct dentry *upperdentry,
>
>  bool ovl_dentry_weird(struct dentry *dentry)
>  {
> +       struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
> +
>         if (!d_can_lookup(dentry) && !d_is_file(dentry) && !d_is_symlink(dentry))
>                 return true;
>
> @@ -210,11 +212,11 @@ bool ovl_dentry_weird(struct dentry *dentry)
>                 return true;
>
>         /*
> -        * Allow filesystems that are case-folding capable but deny composing
> -        * ovl stack from case-folded directories.
> +        * Exceptionally for layers with casefold, we accept that they have
> +        * their own hash and compare operations
>          */
> -       if (sb_has_encoding(dentry->d_sb))
> -               return IS_CASEFOLDED(d_inode(dentry));
> +       if (ofs->casefold)
> +               return false;

I think this is better as:
        if (sb_has_encoding(dentry->d_sb))
                return false;

I don't think there is a reason to test ofs->casefold here.
a "weird" dentry is one that overlayfs doesn't know how to
handle. Now it known how to handle dentries with hash()/compare()
on casefolding capable filesysytems.

Can you please push v6 after this fix to your gitlab branch?

Thanks,
Amir.