[PATCH] nvme: add namespace paths links

[Sagi Grimberg]

>>>>>>> It is really annoying to always have to loop through the entire
>>>>>>> /sys/block directory just to find the namespace path links for
>>>>>>> a single namespace in libnvme/nvme-cli.
>>>>>>> So provide links to the namespace paths for efficient lookup.
>>>>>>>
>>>>>>> Signed-off-by: Hannes Reinecke <hare at suse.de>
>>>>>>> ---
>>>>>>>   drivers/nvme/host/core.c      |  3 +++
>>>>>>>   drivers/nvme/host/multipath.c | 10 ++++++++++
>>>>>>>   2 files changed, 13 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>>>>>>> index 37b6fa746662..88933838e067 100644
>>>>>>> --- a/drivers/nvme/host/core.c
>>>>>>> +++ b/drivers/nvme/host/core.c
>>>>>>> @@ -3681,6 +3681,9 @@ static void nvme_ns_remove(struct nvme_ns *ns)
>>>>>>>       if (!nvme_ns_head_multipath(ns->head))
>>>>>>>           nvme_cdev_del(&ns->cdev, &ns->cdev_device);
>>>>>>> +    else
>>>>>>> +        sysfs_remove_link(&disk_to_dev(ns->head->disk)->kobj,
>>>>>>> +                  ns->disk->disk_name);
>>>>>>>       del_gendisk(ns->disk);
>>>>>>>       down_write(&ns->ctrl->namespaces_rwsem);
>>>>>>> diff --git a/drivers/nvme/host/multipath.c 
>>>>>>> b/drivers/nvme/host/multipath.c
>>>>>>> index 0a88d7bdc5e3..9dd0be645dad 100644
>>>>>>> --- a/drivers/nvme/host/multipath.c
>>>>>>> +++ b/drivers/nvme/host/multipath.c
>>>>>>> @@ -875,6 +875,16 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, 
>>>>>>> __le32 anagrpid)
>>>>>>>       if (blk_queue_is_zoned(ns->queue) && ns->head->disk)
>>>>>>>           ns->head->disk->nr_zones = ns->disk->nr_zones;
>>>>>>>   #endif
>>>>>>> +    if (ns->head->disk) {
>>>>>>
>>>>>> Why are the two conditions not identical?
>>>>>>
>>>>> Which two?
>>>>
>>>> ns->head->disk and nvme_ns_head_multipath()
>>>>
>>> How can we have one without the other? I thought that both are 
>>> mutually dependent .. but yeah, we should be using 
>>> 'nvme_ns_head_multipath()' here.
>>>
>>>>>
>>>>>>> +        int ret;
>>>>>>> +
>>>>>>> +        ret = sysfs_create_link(&disk_to_dev(ns->head->disk)->kobj,
>>>>>>> +                    &disk_to_dev(ns->disk)->kobj,
>>>>>>> +                    ns->disk->disk_name);
>>>>>>> +        if (ret)
>>>>>>> +            dev_warn(ns->ctrl->device,
>>>>>>> +                 "failed to create namespace path link\n");
>>>>>>> +    }
>>>>>>>   }
>>>>>>>   void nvme_mpath_shutdown_disk(struct nvme_ns_head *head)
>>>>>>
>>>>>> What will these links be used for?
>>>>>
>>>>> Mapping for nvme-cli, as explained in the description.
>>>>> Clearly it doesn't do it _now_, but once the patch is in we can
>>>>> simplify nvme-cli to take advantage of it.
>>>>
>>>> you mean for nvme list -v ?
>>>>
>>>> Don't really mind having it, but would want to hear from others as
>>>> well.
>>>
>>> Ok.
>>
>> Hey Hannes,
>> Has this gone anywhere?
> 
> Sadly, no. Everyone said "Yeah, good idea, but let's wait for the 
> others." I _dearly_ would love to have it as it will simplify the
> logic in nvme-cli/libnvme drastically.
> Shall I repost?

Yes, and I personally don't mind having it, so if no one voices
any concern, I don't see why we should prevent it.