Re: [PATCH v5] erofs: use Z_EROFS_LCLUSTER_TYPE_MAX to simplify switches

[Gao Xiang]

Hi Chao,

On 2025/3/16 10:36, Chao Yu wrote:
> On 2025/2/10 11:29, Hongzhen Luo wrote:
> > There's no need to enumerate each type.  No logic changes.
> >
> > Signed-off-by: Hongzhen Luo <hongzhen@xxxxxxxxxxxxxxxxx>
>
> Looks good to me, feel free to add:
>
> Reviewed-by: Chao Yu <chao@xxxxxxxxxx>
>
> And one minor comment below.
>
> > diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
> > index 689437e99a5a..d278ebd60281 100644
> > --- a/fs/erofs/zmap.c
> > +++ b/fs/erofs/zmap.c
> > @@ -265,26 +265,22 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
> >           if (err)
> >               return err;
> > -        switch (m->type) {
> > -        case Z_EROFS_LCLUSTER_TYPE_NONHEAD:
> > +        if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {
> > +            erofs_err(sb, "unknown type %u @ lcn %lu of nid %llu",
> > +                  m->type, lcn, vi->nid);
> > +            DBG_BUGON(1);
> > +            return -EOPNOTSUPP;
>  > +        } else if (m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD) {>               lookback_distance = m->delta[0];
> >               if (!lookback_distance)
> > -                goto err_bogus;
> > +                break;
> >               continue;
> > -        case Z_EROFS_LCLUSTER_TYPE_PLAIN:
> > -        case Z_EROFS_LCLUSTER_TYPE_HEAD1:
> > -        case Z_EROFS_LCLUSTER_TYPE_HEAD2:
> > +        } else {
> >               m->headtype = m->type;
> >               m->map->m_la = (lcn << lclusterbits) | m->clusterofs;
> >               return 0;
> > -        default:
> > -            erofs_err(sb, "unknown type %u @ lcn %lu of nid %llu",
> > -                  m->type, lcn, vi->nid);
> > -            DBG_BUGON(1);
> > -            return -EOPNOTSUPP;
>
> Should return EFSCORRUPTED here? is m->type >= Z_EROFS_LCLUSTER_TYPE_MAX a possible
> case?

It's impossible by the latest on-disk definition, see:
#define Z_EROFS_LI_LCLUSTER_TYPE_MASK	(Z_EROFS_LCLUSTER_TYPE_MAX - 1)

Previously, it was useful before Z_EROFS_LCLUSTER_TYPE_HEAD2 was
introduced, but the `default:` case is already deadcode now.

> Btw, we'd better to do sanity check for m->type in z_erofs_load_full_lcluster(),
> then we can treat m->type as reliable variable later.
>
>      advise = le16_to_cpu(di->di_advise);
>      m->type = advise & Z_EROFS_LI_LCLUSTER_TYPE_MASK;
>      if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {

It's always false here.

Thanks,
Gao Xiang