linux-kernel - Re: [PATCH v6 00/16] nvmet: add target passthru commands support

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Date:   Mon, 29 Jul 2019 10:17:10 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Sagi Grimberg <sagi@...mberg.me>,
        Stephen Bates <sbates@...thlin.com>,
        Hannes Reinecke <hare@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Cc:     Christoph Hellwig <hch@....de>, Keith Busch <kbusch@...nel.org>,
        Jens Axboe <axboe@...com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Max Gurtovoy <maxg@...lanox.com>
Subject: Re: [PATCH v6 00/16] nvmet: add target passthru commands support



On 2019-07-29 10:15 a.m., Sagi Grimberg wrote:
> 
>>> This is different from multipath on say a multi-controller PCI device
>>> and trying to expose both those controllers through passthru. this is
>>> where the problems we are discussing come up.
>>
>> I *think* there is some confusion. I *think* Sagi is talking about network multi-path (i.e. the ability for the host to connect to a controller on the target via two different network paths that fail-over as needed). I *think* Logan is talking about multi-port PCIe NVMe devices that allow namespaces to be accessed via more than one controller over PCIe (dual-port NVMe SSDs being the most obvious example of this today).
> 
> Yes, I was referring to fabrics multipathing which is somewhat
> orthogonal to the backend pci multipathing (unless I'm missing
> something).

Yes, so if we focus on the fabrics multipathing, the only issue I see is
that only one controller can be connected to a passthru target (I
believe this was at your request) so two paths simply cannot exist to
begin with. I can easily remove that restriction.

Logan