[PATCH 2/2] nvme: delete disk when last path is gone

[Sagi Grimberg]

>>> The multipath code currently deletes the disk only after all references
>>> to it are dropped rather than when the last path to that disk is lost.
>>> This differs from the behaviour in the non-multipathed case where the
>>> disk is deleted once the controller is removed.
>>> This has been reported to cause problems with some use cases like MD 
>>> RAID.
>>>
>>> This patch implements an alternative behaviour of deleting the disk when
>>> the last path is gone, ie the same behaviour as non-multipathed nvme
>>> devices. The alternative behaviour can be enabled with the new sysfs
>>> attribute 'no_path_detach'.
>>
>> This looks ok to me. I have heard from a few people that they expected
>> it to work this way with the option enabled, but I suppose we do need to
>> retain the old behavior as default.
>>
>> Reviewed-by: Keith Busch <kbusch at kernel.org>
>>
> Oh, I would _love_ to kill the old behaviour.
> Especially as we now have fast_io_fail_tmo and ctrl_loss_tmo, which 
> gives us enough control on how the controller and the remaining paths 
> should behave (and which weren't present when fabrics got implemented).
> 
> We can make this behaviour the default, and kill the old approach next 
> year if there are no complaints :-)

If this is broken, and this behavior doesn't break anything else then I
don't see why we shouldn't do that.