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

[Christian Brauner <brauner@kernel.org>]

On Mon, Sep 09, 2024 at 02:57:51PM GMT, Christian Brauner 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@kernel.org>
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
> > ---
> >  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.

Forgot:

Reviewed-by: Christian Brauner <brauner@kernel.org>