linux-kernel - Re: [PATCH RFD] alternative kobject release wait mechanism

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Date:	Thu, 19 Apr 2007 15:48:49 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
Cc:	"Tejun Heo" <htejun@...il.com>,
	"Alan Stern" <stern@...land.harvard.edu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Greg K-H" <greg@...ah.com>,
	"Rusty Russell" <rusty@...tcorp.com.au>
Subject: Re: [PATCH RFD] alternative kobject release wait mechanism

On Thu, 19 Apr 2007 09:13:43 -0400,
"Dmitry Torokhov" <dmitry.torokhov@...il.com> wrote:

> Because they are managed by 2 different entities. the struct device
> objects are managed by device core and driver-specific objects are
> managed by their respective driver.

Not sure if I understand you here. My view of this was always that the
embedding object was kind of an extended device and that the relevant
driver/subsystem managed it through the driver core infrastructure.

> 
> > > Pretty much drivers have 2 options:
> > >
> > > struct my_device {
> > >         void *private_data;
> > >         struct device dev;
> > > };
> > >
> > > In this case ->release must live in a subsystem code; individual
> > > drivers kfree(my_dev->private) and do any additional cleanup after
> > > calling device_unregister(&my_dev->dev);
> >
> > They must do this in the ->remove callback.
> 
> Why? If the driver truly stops hardware then any driver-specific data
> is not needed. With sysfs severing access to removed attributes there
> is no need to gave "global release", cleanup can be done in stages.

I think I meant the same thing :) Freeing the data in the ->release
callback is obviously too late. Freeing it in the ->remove callback
means that the device is no longer really used (and can't be looked up
any more); only some further refrences may linger (and those are of no
consequence with the sysfs disconnect).
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