Re: [PATCH 02/10] fs: add path_create(), path_move() and path_clone()

[NeilBrown]

On Tue, 15 Sep 2026, NeilBrown wrote:
> On Mon, 14 Sep 2026, Mateusz Guzik wrote:
> > Signed-off-by: Mateusz Guzik <mjguzik@xxxxxxxxx>
> > ---
> >  fs/namei.c           | 29 +++++++++++++++++++++++++++++
> >  include/linux/path.h | 14 ++++++++++++--
> >  2 files changed, 41 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/namei.c b/fs/namei.c
> > index ca4f5e3be99a..c8754c7ba8be 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -698,6 +698,35 @@ static __always_inline int lookup_inode_permission_may_exec(struct mnt_idmap *id
> >  	return security_inode_permission(inode, mask);
> >  }
> >  
> > +/**
> > + * path_create - WRITEME
> > + * @path: path to get the reference to
> > + * @mnt: WRITEME
> > + * @dentry: WRITEME
> > + *
> > + * Create a path object using the given vfsmount and dentry pair while incrementing
> > + * the reference count on both.
> > + */
> > +void path_create(struct path *path, struct vfsmount *mnt, struct dentry *dentry)
> > +{
> > +	path->mnt = mntget(mnt);
> > +	path->dentry = dget(dentry);
> > +}
> > +EXPORT_SYMBOL(path_create);
> > +
> > +/**
> > + * path_clone - WRITEME
> > + * @path: path to get the reference to
> > + *
> > + * Given a path increment the reference count to the dentry and the vfsmount.
> > + */
> > +void path_clone(const struct path *src, struct path *dst)
> > +{
> > +	dst->mnt = mntget(src->mnt);
> > +	dst->dentry = dget(src->dentry);
> > +}
> > +EXPORT_SYMBOL(path_clone);
> > +
> >  /**
> >   * path_get - get a reference to a path
> >   * @path: path to get the reference to
> > diff --git a/include/linux/path.h b/include/linux/path.h
> > index 7ea389dc764b..8a621e0e1921 100644
> > --- a/include/linux/path.h
> > +++ b/include/linux/path.h
> > @@ -10,8 +10,18 @@ struct path {
> >  	struct dentry *dentry;
> >  } __randomize_layout;
> >  
> > -extern void path_get(const struct path *);
> > -extern void path_put(const struct path *);
> > +void path_create(struct path *, struct vfsmount *, struct dentry *);
> > +void path_clone(const struct path *, struct path *);
> > +void path_get(const struct path *);
> > +void path_put(const struct path *);
> > +
> > +static inline void path_move(struct path *src, struct path *dst)
> 
> Oh ...  this is backwards.  At least is it backwards compared to
> memmove().  I understand different people will read "move" differently
> and would prefer to avoid it.
> Can we do without it?  You only seem to use it in one place.
> 
> How would you feel about:
> 
>  struct path path_move_from(struct path *src)
>  {
> 	struct path ret = *src;
> 	src->mnt = NULL;
> 	src->dentry = NULL;
> 	return ret;
>  }
> 
> and then use
> 
>  file->__f_path = path_move_from(path);
> 
> ??

And then of course there is path_clone() which looks backwards to me.
Can we just change path_get() to return the path, like a lot of
FOO_get() functions do, and use
   newpath = path_clone(old_path);
??

Thanks,
NeilBrown