nvme reservation commands during controller reset

[Sagi Grimberg]

>>> Amit,
>>>
>>> can you try the branch below?  Pretty much hot off the press, but I
>>> think this should address your problem:
>>>
>>> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/nvme-pr-fix
>>
>> I like the approach, but I think we'll need a bit more path awareness
>> like we check for available paths if we requeue or fail..
> 
> If there is no available path, nvme_find_path will fail and thus we'll
> error it.  This is the same mechanism as used by
> nvme_ns_head_submit_bio.

nvme_find_path will return ns=NULL even if none of the paths is LIVE,
but we want to requeue if we have an available path (e.g. ANA state is
inaccessible temporarily or ctrl state is RESETTING/CONNECTING).

Only if no path is available for request execution we are failing the
request.

If we are providing multipathing for reservations, we should give
the same efforts as we do for normal I/O. This could mean waiting
for some indication on the ns path states (wait for a completion in
nvme_submit_sync_cmd_disk and wake it up in nvme_mpath_set_live).