[PATCH for-next 4/4] nvme-multipath: add multipathing for uring-passthrough commands

[Sagi Grimberg]

>> However io_kiocb is less
>> constrained, and could be used as a context to hold such a space.
>>
>> Even if it is undesired to have io_kiocb be passed to uring_cmd(), it
>> can still hold a driver specific space paired with a helper to obtain it
>> (i.e. something like io_uring_cmd_to_driver_ctx(ioucmd) ). Then if the
>> space is pre-allocated it is only a small memory copy for a stable copy
>> that would allow a saner failover design.
> 
> I am thinking along the same lines, but it's not about few bytes of
> space rather we need 80 (72 to be precise). Will think more, but
> these 72 bytes really stand tall in front of my optimism.

You don't have to populate this space on every I/O, you can just
populate it when there is no usable path and when you failover a
request...