linux-kernel - Re: [PATCH] char: misc: assign file->private

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Date:	Tue, 25 Jun 2013 11:59:44 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	Samu Onkalo <samu.p.onkalo@...ia.com>,
	michael.opdenacker@...e-electrons.com,
	gregory.clement@...e-electrons.com,
	maxime.ripard@...e-electrons.com,
	alexandre.belloni@...e-electrons.com
Subject: Re: [PATCH] char: misc: assign file->private_data in all cases

Dear Greg Kroah-Hartman,

On Mon, 24 Jun 2013 15:26:42 -0700, Greg Kroah-Hartman wrote:

> > However, this assignment was only done when the misc driver was
> > declaring a driver-specific ->open() operation in its
> > file_operations. This doesn't make sense, as the driver may not
> > necessarily have a custom ->open() operation, and might still be
> > interested in having file->private_data properly set for use in its
> > ->read() and write() operations.
> > 
> > Therefore, we move the assignment of file->private_data outside of the
> > condition that tests whether a driver-specific ->open() operation was
> > defined.
> 
> Does this solve a problem with an existing misc driver?  Or are you just
> trying to be "safe" for future, broken, drivers?

This problem was spotted while implementing a dummy/example misc driver
for training purposes. I am not aware of any mainline misc driver
affected by this problem, but I haven't reviewed all misc drivers.

It simply seems to make sense to implement the feature of fa1f68db6ca
("drivers: misc: pass miscdevice pointer via file private data") in a
way that also allows misc drivers that do not provide their own
->open() operation to use it.

That said, I'm not sure why you call such drivers 'broken'.

Best regards,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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