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Subject: Re: [PATCH v7 08/14] nvmet-core: allow one host per passthru-ctrl
To:     Max Gurtovoy <maxg@mellanox.com>,
        Logan Gunthorpe <logang@deltatee.com>,
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Cc:     Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
        Stephen Bates <sbates@raithlin.com>, Jens Axboe <axboe@fb.com>,
        Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de>
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From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <24e2ddd0-4b2a-8092-cf91-df8c0fb482e5@grimberg.me>
Date:   Thu, 22 Aug 2019 10:41:09 -0700
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>>> I don't understand why we don't limit a regular ctrl to single access 
>>> and we do it for the PT ctrl.
>>>
>>> I guess the block layer helps to sync between multiple access in 
>>> parallel but we can do it as well.
>>>
>>> Also, let's say you limit the access to this subsystem to 1 user, the 
>>> bdev is still accessibly for local user and also you can create a 
>>> different subsystem that will use this device (PT and non-PT ctrl).
>>>
>>> Sagi,
>>>
>>> can you explain the trouble you meant and how this limitation solve it ?
>>
>> Its different to emulate the controller with all its admin
>> commands vs. passing it through to the nvme device.. (think of format 
>> nvm)
>>
>>
>>
> we don't need to support format command for PT ctrl as we don't support 
> other commands such create_sq/cq.

That is just an example, basically every command that we are not aware
of we simply passthru to the drive without knowing the implications
on a multi-host environment..