[PATCH RFC 0/1] Add visibility for native NVMe miltipath using debugfs

[Sagi Grimberg]

> # cat /sys/kernel/debug/block/nvme2n2/multipath
> io-policy: numa
> io-path:
> --------
> node  current-path  ctrl    ana-state
> 2     nvme2c2n2     nvme2   optimized
> 3     nvme2c0n2     nvme0   optimized
>
> The above output shows that current selected iopolicy is numa. And when we
> have workload running I/O on numa node 2, accessing namespace "nvme2n2",
> it uses path nvme2c2n2 and controller nvme2 for forwarding data. Moreover
> the current ana-state for this path is optimized. Similarly, for I/O
> workload running on numa node 3 would use path nvme2c0n2 and controller
> nvme0.
>
> Now changing the iopolicy to round-robin,
>
> # echo "round-robin" > /sys/class/nvme-subsystem/nvme-subsys2/iopolicy
>
> # cat /sys/kernel/debug/block/nvme2n2/multipath
> io-policy: round-robin
> io-path:
> --------
> node  rr-path       ctrl    ana-state
> 2     nvme2c2n2     nvme2   optimized
> 2     nvme2c0n2     nvme0   optimized
> 3     nvme2c2n2     nvme2   optimized
> 3     nvme2c0n2     nvme0   optimized

Can we avoid a formatted output in sysfs? I'd much rather prefer that 
nvme-cli/libnvme to
format this (maybe this may be wanted as json in the future for example)...

Can we simply expose the individual components and have userpace format 
the output?