netdev - RE: [CRAZY-RFF] debugfs: track open files and release on remove

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Date:   Fri, 9 Oct 2020 09:00:41 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Johannes Berg' <johannes@...solutions.net>,
        Greg KH <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nstange@...e.de" <nstange@...e.de>,
        "ap420073@...il.com" <ap420073@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "rafael@...nel.org" <rafael@...nel.org>
Subject: RE: [CRAZY-RFF] debugfs: track open files and release on remove

From: Johannes Berg
> Sent: 09 October 2020 09:45
> 
> On Fri, 2020-10-09 at 08:34 +0000, David Laight wrote:
> >
...
> > Does it ever make any sense to set .owner to anything other than
> > THIS_MODULE?
> 
> No. But I believe THIS_MODULE is NULL for built-in code, so we can't
> just WARN_ON(!fops->owner).
...
> > I was also wondering if this affects normal opens?
> > They should hold a reference on the module to stop it being unloaded.
> > Does that rely on .owner being set?
> 
> Yes.

Sound like the module load code should be verifying it then.

Looking at one of my modules (which does set .owner).
Perhaps cdev_init() could be a #define that picks up THIS_MODULE.
This could then be checked against the one in fops or saved
in the 'struct cdev'.

I presume debugfs (which I've not used) has some similar calls.

	David

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