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Subject: Re: [PATCH v6 04/16] nvme-core: introduce nvme_get_by_path()
To:     Keith Busch <kbusch@kernel.org>,
        Logan Gunthorpe <logang@deltatee.com>
Cc:     Matthew Wilcox <willy@infradead.org>, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        Jens Axboe <axboe@fb.com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
        Max Gurtovoy <maxg@mellanox.com>,
        Stephen Bates <sbates@raithlin.com>
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 <20190725175023.GA30641@bombadil.infradead.org>
 <da58f91e-6cfa-02e0-dd89-3cfa23764a0e@deltatee.com>
 <20190725195835.GA7317@localhost.localdomain>
From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <0b7e5d9f-207c-ee4e-a992-024c178cdd49@grimberg.me>
Date:   Thu, 25 Jul 2019 13:12:32 -0700
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>>>> nvme_get_by_path() is analagous to blkdev_get_by_path() except it
>>>> gets a struct nvme_ctrl from the path to its char dev (/dev/nvme0).
>>>>
>>>> The purpose of this function is to support NVMe-OF target passthru.
>>>
>>> I can't find anywhere that you use this in this patchset.
>>>
>>
>> Oh sorry, the commit message is out of date the function was actually
>> called nvme_ctrl_get_by_path() and it's used in Patch 10.
> 
> Instead of by path, could we have configfs take something else, like
> the unique controller instance or serial number? I know that's different
> than how we handle blocks and files, but that way nvme core can lookup
> the cooresponding controller without adding new cdev dependencies.

We could... but did we find sufficient justification to have the user
handle passthru devices differently than any other backend?
once we commit to an interface its very hard to change.