Re: [PATCHv3 2/4] nvme: extend show-topology command to add support for multipath

[Hannes Reinecke <hare@suse.de>]

On 9/4/25 19:56, 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.
> 
> Examples:
> 
> $ 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>
>         /              /      /
>        |              /      /
>   +- nvme2n1 (ns 1)  /      /
>   \                 |      |
>    +- nvme2c2n1 optimized 1,2 nvme2 tcp traddr=127.0.0.2,trsvcid=4460,src_addr=127.0.0.1 live
>    +- nvme2c3n1 optimized 3,4 nvme3 tcp traddr=127.0.0.3,trsvcid=4460,src_addr=127.0.0.1 live
> 
> For iopolicy=numa, only NUMA node list is shown (queue depth is hidden).
> 
> $ nvme show-topology -r multipath
> 
> nvme-subsys2 - NQN=nvmet_subsystem
>                 hostnqn=nqn.2014-08.org.nvmexpress:uuid:12b49f6e-0276-4746-b10c-56815b7e6dc2
>                 iopolicy=queue-depth
> 
>            _ _ _<head-node>
>           /              _ _ _ <ana-state>
>          /              /
>         /              /     _ _ _<queue-depth>
>        |              /     /
>   +- nvme2n1 (ns 1)  /     /
>   \                 |     |
>    +- nvme2c2n1 optimized 0 nvme2 tcp traddr=127.0.0.2,trsvcid=4460,src_addr=127.0.0.1 live
>    +- nvme2c3n1 optimized 0 nvme3 tcp traddr=127.0.0.3,trsvcid=4460,src_addr=127.0.0.1 live
> 
> For iopolicy=queue-depth, queue depth is shown (NUMA node list is hidden).
> 
> $ nvme show-topology -r multipath
> 
> nvme-subsys2 - NQN=nvmet_subsystem
>                 hostnqn=nqn.2014-08.org.nvmexpress:uuid:12b49f6e-0276-4746-b10c-56815b7e6dc2
>                 iopolicy=round-robin
> 
>            _ _ _<head-node>
>           /              _ _ _ <ana-state>
>          /              /
>         /              /
>        |              /
>   +- nvme2n1 (ns 1)  /
>   \                 |
>    +- nvme2c2n1 optimized nvme2 tcp traddr=127.0.0.2,trsvcid=4460,src_addr=127.0.0.1 live
>    +- nvme2c3n1 optimized nvme3 tcp traddr=127.0.0.3,trsvcid=4460,src_addr=127.0.0.1 live
> 
> For iopolicy=round-robin, both NUMA node list and queue depth are hidden.
> 
> Note:
> The annotations above (e.g., <numa-node-list>, <ana-state>, <head-node>,
> <queue-depth>) are for illustration only and are not part of the actual
> command output. A more human-friendly tabular format will be introduced
> in a follow-up patches.
> 
> Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
> ---
>   nvme-print-binary.c |  1 +
>   nvme-print-json.c   | 36 +++++++++++++++----
>   nvme-print-stdout.c | 85 ++++++++++++++++++++++++++++++++++++++++++---
>   nvme-print.c        |  4 ++-
>   nvme-print.h        |  1 +
>   nvme.c              |  4 ++-
>   nvme.h              |  1 +
>   7 files changed, 120 insertions(+), 12 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

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