linux-kernel - Re: [PATCH 1/3] cdev: Finish the cdev api with queued mode support

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Date:   Thu, 21 Jan 2021 09:50:09 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dave Jiang <dave.jiang@...el.com>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH 1/3] cdev: Finish the cdev api with queued mode support

On Thu, Jan 21, 2021 at 12:13 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Jan 20, 2021 at 11:38:57AM -0800, Dan Williams wrote:
> > -void cdev_del(struct cdev *p)
> > +void cdev_del(struct cdev *cdev)
> >  {
> > -     cdev_unmap(p->dev, p->count);
> > -     kobject_put(&p->kobj);
> > +     cdev_unmap(cdev->dev, cdev->count);
> > +     kobject_put(&cdev->kobj);
>
> After Christoph's patch series, the kobject in struct cdev does nothing,
> so I will be removing it.  So I don't think this patch set is going to
> do what you want :(

The proposal in this series has nothing to do with kobject lifetime.
Please take another look at the file_operations shutdown coordination
problem and the fact that it's not just cdev that has a use case to
manage file_operations this way. I believe Christoph's only objection,
correct me if I'm wrong, is that this proposal invents a new third way
to do this relative to procfs and debugfs. Perhaps there's a way to
generalize this for all three, and I'm going to put some thought
there, but at this point I think I'm failing to describe the problem
clearly.