Re: [PATCH v2 04/19] libmpathutil: add implementation of generic shared pointer

On Wed, 2026-05-27 at 19:16 -0400, Benjamin Marzinski wrote:
> On Fri, May 22, 2026 at 06:44:00PM +0200, Martin Wilck wrote:
> > Add a set of simple functions to handle refcounted pointers.
> > 
> > Signed-off-by: Martin Wilck <[email protected]>
> > Reviewed-by: Benjamin Marzinski <[email protected]>
> > ---
> >  libmpathutil/libmpathutil.version |  7 +++++
> >  libmpathutil/util.c               | 45
> > ++++++++++++++++++++++++++++---
> >  libmpathutil/util.h               |  5 ++++
> >  3 files changed, 53 insertions(+), 4 deletions(-)
> > 
> > diff --git a/libmpathutil/util.c b/libmpathutil/util.c
> > index 23a9797..3c623ec 100644
> > --- a/libmpathutil/util.c
> > +++ b/libmpathutil/util.c
> > @@ -384,3 +382,42 @@ void cleanup_udev_device(struct udev_device
> > **udd)
> >  	if (*udd)
> >  		udev_device_unref(*udd);
> >  }
> > +
> > +struct shared_ptr {
> > +	long refcnt;
> > +	void (*destructor)(void *);
> > +	char __attribute__((aligned(sizeof(void *)))) ptr[];
> > +};
> > +
> > +void *alloc_shared_ptr(size_t size, void (*destructor)(void *))
> > +{
> > +	struct shared_ptr *sp = malloc(sizeof(*sp) + size);
> > +
> > +	if (!sp)
> > +		return NULL;
> > +	uatomic_set(&sp->refcnt, 1);
> > +	sp->destructor = destructor;
> > +	return sp->ptr;
> > +}
> > +
> > +void get_shared_ptr(void *ptr)
> > +{
> 
> We should probably return here if ptr is NULL, like we do in
> put_shared_ptr(). Alternatively, this might be a reasonable place for
> an
> assert(), since nobody should be calling these with NULL pointers.

That makes sense. I'll add an assert(), and change put_shared_ptr()
accordingly.

Martin