linux-kernel - Re: [PATCH v6 04/16] nvme-core: introduce nvme_get_by

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Date:   Thu, 25 Jul 2019 14:31:18 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>, Jens Axboe <axboe@...com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v6 04/16] nvme-core: introduce nvme_get_by_path()

On Thu, Jul 25, 2019 at 02:28:28PM -0600, Logan Gunthorpe wrote:
> 
> 
> On 2019-07-25 1:58 p.m., Keith Busch wrote:
> > On Thu, Jul 25, 2019 at 11:54:18AM -0600, Logan Gunthorpe wrote:
> >>
> >>
> >> On 2019-07-25 11:50 a.m., Matthew Wilcox wrote:
> >>> On Thu, Jul 25, 2019 at 11:23:23AM -0600, Logan Gunthorpe wrote:
> >>>> 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 Oh sorry, the commit message is out of date the function was actually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.
> 
> Well the previous version of the patchset just used the ctrl name
> ("nvme1") and looped through all the controllers to find a match. But
> this sucks because of the inconsistency and the fact that the name can
> change if hardware changes and the number changes. Allowing the user to
> make use of standard udev rules seems important to me.

Should we then create a new udev rule for persistent controller
names? /dev/nvme1 may not be the same controller each time you refer
to it.