Re: [PATCH v1 2/3] fs/mnt_idmapping: introduce an invalid_mnt_idmap

[Aleksandr Mikhalitsyn]

On Mon, Sep 9, 2024 at 2:57 PM Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
> On Fri, Sep 06, 2024 at 04:34:52PM GMT, Alexander Mikhalitsyn wrote:
> > Link: https://lore.kernel.org/linux-fsdevel/20240904-baugrube-erhoben-b3c1c49a2645@brauner/
> > Suggested-by: Christian Brauner <brauner@xxxxxxxxxx>
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> > ---
> >  fs/mnt_idmapping.c            | 22 ++++++++++++++++++++--
> >  include/linux/mnt_idmapping.h |  1 +
> >  2 files changed, 21 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/mnt_idmapping.c b/fs/mnt_idmapping.c
> > index 3c60f1eaca61..cbca6500848e 100644
> > --- a/fs/mnt_idmapping.c
> > +++ b/fs/mnt_idmapping.c
> > @@ -32,6 +32,15 @@ struct mnt_idmap nop_mnt_idmap = {
> >  };
> >  EXPORT_SYMBOL_GPL(nop_mnt_idmap);
> >
> > +/*
> > + * Carries the invalid idmapping of a full 0-4294967295 {g,u}id range.
> > + * This means that all {g,u}ids are mapped to INVALID_VFS{G,U}ID.
> > + */
> > +struct mnt_idmap invalid_mnt_idmap = {
> > +     .count  = REFCOUNT_INIT(1),
> > +};
> > +EXPORT_SYMBOL_GPL(invalid_mnt_idmap);
> > +
> >  /**
> >   * initial_idmapping - check whether this is the initial mapping
> >   * @ns: idmapping to check
> > @@ -75,6 +84,8 @@ vfsuid_t make_vfsuid(struct mnt_idmap *idmap,
> >
> >       if (idmap == &nop_mnt_idmap)
> >               return VFSUIDT_INIT(kuid);
> > +     if (idmap == &invalid_mnt_idmap)
> > +             return INVALID_VFSUID;
>
> Could possibly deserve an:
>
> if (unlikely(idmap == &invalid_mnt_idmap))
>         return INVALID_VFSUID;
>
> and technically I guess we could also do:
>
> if (likely(idmap == &nop_mnt_idmap))
>         return VFSUIDT_INIT(kuid);
>
> but not that relevant for this patch.

Yeah, I'm happy to submit that change (if you don't mind) a bit later
when this will be merged,
cause in this case we can add this likely()/unlikely() at once for
both nop_mnt_idmap/invalid_mnt_idmap.

Kind regards,
Alex