Re: [PATCH v6 5/9] ovl: Ensure that all layers have the same encoding

[Amir Goldstein <amir73il@gmail.com>]

On Mon, Aug 25, 2025 at 1:17 PM Gabriel Krisman Bertazi
<gabriel@krisman.be> wrote:
>
> André Almeida <andrealmeid@igalia.com> writes:
>
> > When merging layers from different filesystems with casefold enabled,
> > all layers should use the same encoding version and have the same flags
> > to avoid any kind of incompatibility issues.
> >
> > Also, set the encoding and the encoding flags for the ovl super block as
> > the same as used by the first valid layer.
> >
> > Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> > Signed-off-by: André Almeida <andrealmeid@igalia.com>
> > ---
> >  fs/overlayfs/super.c | 25 +++++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> >
> > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> > index df85a76597e910d00323018f1d2cd720c5db921d..b1dbd3c79961094d00c7f99cc622e515d544d22f 100644
> > --- a/fs/overlayfs/super.c
> > +++ b/fs/overlayfs/super.c
> > @@ -991,6 +991,18 @@ static int ovl_get_data_fsid(struct ovl_fs *ofs)
> >       return ofs->numfs;
> >  }
> >
> > +/*
> > + * Set the ovl sb encoding as the same one used by the first layer
> > + */
> > +static void ovl_set_encoding(struct super_block *sb, struct super_block *fs_sb)
> > +{
> > +#if IS_ENABLED(CONFIG_UNICODE)
> > +     if (sb_has_encoding(fs_sb)) {
> > +             sb->s_encoding = fs_sb->s_encoding;
> > +             sb->s_encoding_flags = fs_sb->s_encoding_flags;
> > +     }
> > +#endif
> > +}
> >
> >  static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> >                         struct ovl_fs_context *ctx, struct ovl_layer *layers)
> > @@ -1024,6 +1036,9 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> >       if (ovl_upper_mnt(ofs)) {
> >               ofs->fs[0].sb = ovl_upper_mnt(ofs)->mnt_sb;
> >               ofs->fs[0].is_lower = false;
> > +
> > +             if (ofs->casefold)
> > +                     ovl_set_encoding(sb, ofs->fs[0].sb);
> >       }
> >
> >       nr_merged_lower = ctx->nr - ctx->nr_data;
> > @@ -1083,6 +1098,16 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> >               l->name = NULL;
> >               ofs->numlayer++;
> >               ofs->fs[fsid].is_lower = true;
> > +
> > +             if (ofs->casefold) {
> > +                     if (!ovl_upper_mnt(ofs) && !sb_has_encoding(sb))
> > +                             ovl_set_encoding(sb, ofs->fs[fsid].sb);
> > +
> > +                     if (!sb_has_encoding(sb) || !sb_same_encoding(sb, mnt->mnt_sb)) {
>
> Minor nit, but isn't the sb_has_encoding()  check redundant here?  sb_same_encoding
> will check the sb->encoding matches the mnt_sb already.

Maybe we did something wrong but the intention was:
If all layers root are casefold disabled (or not supported) then
a mix of layers with fs of different encoding (and fs with no encoding support)
is allowed because we take care that all directories are always
casefold disabled.

Thanks,
Amir.