[SPDK] Re: NVMe Multipath subsystem controller IDs

On 01/04/2021 22:57, Walker, Benjamin wrote:
> Exposing the same subsystem from two nodes is still certainly problematic. I think all of the
> issues I listed in that thread are still valid (reservations, discovery, etc.) A better solution is likely
> namespaces shared across subsystems, but that is not in the NVMe specification today.

Understood, we have solutions being considered for other issues 
(essentially something to orchestrate the multiple SPDK instances).

> Could we make an API in include/spdk/nvmf.h to allow the user to register a function pointer for generating
> the controller ids? Maybe just stick a function pointer into spdk_nvmf_target_opts. Then you can use whatever
> algorithm you want. How does that sound?

That's certainly another option and gives maximum flexibility though it 
means a standalone, unmodified SPDK can only used the built-in 
controller ID generation function, perhaps ruling out some quick 
experiments.

I have already implemented the per-subsystem controller ID range in SPDK 
and it is a fairly small patch. It gives some flexibility without having 
the complexity of having to supply your own implementation of controller 
ID generation and maintaining the state of that per-subsystem.