Re: [PATCH 02/19] nvme: introduce a namespace count in the ns head structure

[John Garry]

On 02/03/2026 12:46, Nilay Shroff wrote:
> > Signed-off-by: John Garry<john.g.garry@xxxxxxxxxx>
> > ---
> >   drivers/nvme/host/core.c      | 10 +++++++---
> >   drivers/nvme/host/multipath.c |  4 ++--
> >   drivers/nvme/host/nvme.h      |  1 +
> >   3 files changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> > index 37e30caff4149..76249871dd7c2 100644
> > --- a/drivers/nvme/host/core.c
> > +++ b/drivers/nvme/host/core.c
> > @@ -4024,7 +4024,7 @@ static int nvme_init_ns_head(struct nvme_ns *ns, 
> > struct nvme_ns_info *info)
> >       } else {
> >           ret = -EINVAL;
> >           if ((!info->is_shared || !head->shared) &&
> > -            !list_empty(&head->list)) {
> > +            head->ns_count) {
> >               dev_err(ctrl->device,
> >                   "Duplicate unshared namespace %d\n",
> >                   info->nsid);
> > @@ -4047,6 +4047,7 @@ static int nvme_init_ns_head(struct nvme_ns *ns, 
> > struct nvme_ns_info *info)
> >       }
> >       list_add_tail_rcu(&ns->siblings, &head->list);
> > +    head->ns_count++;
> >       ns->head = head;
> >       mutex_unlock(&ctrl->subsys->lock);
>
> I think we could still access head->mpath_disk->mpath_head->dev_list.
> So in that case do we really need to have ->ns_count? 

As mentioned, if CONFIG_NVME_MULTIPATH is disabled, mpath_head->dev_list 
is not maintained. So we need another method to set NS count in the core 
code.

> Moreover, if
> we could maintain a pointer to struct mpath_head from struct 
> nvme_ns_head then we may avoid one dereference. What do you think?

I think that it should be ok. I was just trying to reduce pointer 
declaration (as they need to be maintained).

Thanks!