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

[Nilay Shroff <nilay@linux.ibm.com>]

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.

Thanks,
--Nilay