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

[John Garry <john.g.garry@oracle.com>]

On 02/03/2026 12:46, Nilay Shroff wrote:
>>
>> Signed-off-by: John Garry<john.g.garry@oracle.com>
>> ---
>>   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!