[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()

> 
>>> +        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.