linux-kernel - Re: [PATCH v6 02/16] chardev: introduce cdev_get_by

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Date:   Thu, 25 Jul 2019 10:58:34 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.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>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Stephen Bates <sbates@...thlin.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v6 02/16] chardev: introduce cdev_get_by_path()

On Thu, Jul 25, 2019 at 11:53:20AM -0600, Logan Gunthorpe wrote:
> 
> 
> On 2019-07-25 11:40 a.m., Greg Kroah-Hartman wrote:
> > On Thu, Jul 25, 2019 at 11:23:21AM -0600, Logan Gunthorpe wrote:
> >> cdev_get_by_path() attempts to retrieve a struct cdev from
> >> a path name. It is analagous to blkdev_get_by_path().
> >>
> >> This will be necessary to create a nvme_ctrl_get_by_path()to
> >> support NVMe-OF passthru.
> > 
> > Ick, why?  Why would a cdev have a "pathname"?
> 
> So we can go from "/dev/nvme0" (which points to a char device) to its
> struct cdev and eventually it's struct nvme_ctrl. Doing it this way also
> allows supporting symlinks that might be created by udev rules.

But you're not really trying to go from a string to a chardev.  You're
trying to go from a nvmet_subsys to a chardev.  Isn't there a better
way to link the two somewhere else?

(I must confess that once I would have known the answer to this, but
the NVMe subsystem has grown ridiculously complex and I can no longer
fit it in my head)