[PATCHv2 2/4] nvme: extend show-topology command to add support for multipath

[Hannes Reinecke]

On 8/19/25 06:49, Nilay Shroff wrote:
> 
> 
> On 8/18/25 12:52 PM, Hannes Reinecke wrote:
>> On 8/12/25 14:56, Nilay Shroff wrote:
>>> This commit enhances the show-topology command by adding support for
>>> NVMe multipath. With this change, users can now list all paths to a
>>> namespace from its corresponding head node device. Each NVMe path
>>> entry then also includes additional details such as ANA state, NUMA
>>> node, and queue depth, improving visibility into multipath configs.
>>> This information can be particularly helpful for debugging and
>>> analyzing NVMe multipath setups.
>>>
>>> To support this functionality, the "--ranking" option of the nvme
>>> show-topology command has been extended with a new sub-option:
>>> "multipath".
>>>
>>> Since this enhancement is specific to NVMe multipath, the iopolicy
>>> configured under each subsystem is now always displayed. Previously,
>>> iopolicy was shown only with nvme show-topology verbose output, but
>>> it is now included by default to improve usability and provide better
>>> context when reviewing multipath configurations via show-topology.
>>>
>>> With this update, users can view the multipath topology of a multi
>>> controller/port NVMe disk using:
>>>
>>> $ nvme show-topology -r multipath
>>>
>>> nvme-subsys2 - NQN=nvmet_subsystem
>>>                  hostnqn=nqn.2014-08.org.nvmexpress:uuid:12b49f6e-0276-4746-b10c-56815b7e6dc2
>>>                  iopolicy=numa
>>>
>>>             _ _ _<head-node>
>>>            /              _ _ _ <ana-state>
>>>           /              /      _ _ _ <numa-node-list>
>>>          /              /      /  _ _ _<queue-depth>
>>>         |              /      /  /
>>>    +- nvme2n1 (ns 1)  /      /  /
>>>    \                 |      |  |
>>>     +- nvme2c2n1 optimized 1,2 0 nvme2 tcp traddr=127.0.0.2,trsvcid=4460,src_addr=127.0.0.1 live
>>>     +- nvme2c3n1 optimized 3,4 0 nvme3 tcp traddr=127.0.0.3,trsvcid=4460,src_addr=127.0.0.1 live
>>>
>>> Please note that the annotations shown above (e.g., <numa-node-list>,
>>> <ana-state>, <hed-node>, and <queue-depth>) are included for clarity
>>> only and are not part of the actual output.
>>>
>>
>> Hmm. Why do we have the values for 'numa-node-list' and 'queue-depth'
>> both in here? They are tied to the selected IO policy, and pretty
>> meaningless if that IO policy is not selected.
>> Please include only the values relevant for the selected IO policy;
>> this will increase readability of the resulting status string.
>>
> Okay makes sense, so we'd print <numa-node> and exclude <queue-depth> if iopolicy
> is numa. For 'queue-depth' iopolicy, we'd print <queue-depth> and exclude <numa-node>.
> And for 'round-robin' iopolicy, we'd neither print <numa-node> nor <queue-depth>.
> I'll update this in the next patch.
> 
Hmm. I'd rather have _some_ value for 'round-robin', too, as otherwise
the number of fields will be different (and making parsing harder).

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare at suse.de                                +49 911 74053 688
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