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

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Message-ID: <24e2ddd0-4b2a-8092-cf91-df8c0fb482e5@grimberg.me>
Date:   Thu, 22 Aug 2019 10:41:09 -0700
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Max Gurtovoy <maxg@...lanox.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Stephen Bates <sbates@...thlin.com>, Jens Axboe <axboe@...com>,
        Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v7 08/14] nvmet-core: allow one host per passthru-ctrl


>>> 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..