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To:     Sagi Grimberg <sagi@grimberg.me>, Max Gurtovoy <maxg@mellanox.com>,
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From:   Logan Gunthorpe <logang@deltatee.com>
Message-ID: <5e53b732-5c33-c331-0c77-d52d5075306a@deltatee.com>
Date:   Thu, 22 Aug 2019 13:41:32 -0600
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Subject: Re: [PATCH v7 08/14] nvmet-core: allow one host per passthru-ctrl
Sender: linux-kernel-owner@vger.kernel.org
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On 2019-08-22 1:17 p.m., Sagi Grimberg wrote:
> 
>>>>> 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..
> 
> If we were to change the logic of nvmet_parse_passthru_admin_cmd to
> have the default case do nvmet_parse_admin_cmd, and only have
> the vendor-specific space opcodes do nvmet_passthru_execute_cmd
> then I could not see at the moment how we can break a multi-host
> export...

That makes sense. I'll make that change and resend a v8 next week.

Logan