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To:     Keith Busch <keith.busch@intel.com>
Cc:     linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>, Jens Axboe <axboe@fb.com>,
        Keith Busch <kbusch@kernel.org>,
        Hannes Reinecke <hare@suse.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>
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 <20190831152910.GA29439@localhost.localdomain>
From:   Logan Gunthorpe <logang@deltatee.com>
Message-ID: <33af4d94-9f6d-9baa-01fa-0f75ccee263e@deltatee.com>
Date:   Tue, 3 Sep 2019 10:08:01 -0600
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Subject: Re: [PATCH] nvme-core: Fix subsystem instance mismatches
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On 2019-08-31 9:29 a.m., Keith Busch wrote:
> On Fri, Aug 30, 2019 at 06:01:39PM -0600, Logan Gunthorpe wrote:
>> To fix this, assign the subsystem's instance based on the instance
>> number of the controller's instance that first created it. There should
>> always be fewer subsystems than controllers so the should not be a need
>> to create extra subsystems that overlap existing controllers.
> 
> The subsystem's lifetime is not tied to the controller's. When the
> controller is removed and releases its instance, the next controller
> to take that available instance will create naming collisions with the
> subsystem still using it.
> 

Hmm, yes, ok.

So perhaps we can just make the subsystem prefer the ctrl's instance
when allocating the ID? Then at least, in the common case, the
controller numbers will match the subsystem numbers. Only when there's
random hot-plugs would the numbers get out of sync.

Logan