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SubjectRe: [PATCH v7 08/14] nvmet-core: allow one host per passthru-ctrl


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

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