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

[Hannes Reinecke]

On 2/25/21 5:59 PM, Keith Busch wrote:
> On Thu, Feb 25, 2021 at 12:05:34PM +0100, Hannes Reinecke wrote:
>> 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 :-)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
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