linux-kernel - Re: [PATCH RFC 1/8] Introduce dynamic clock devices

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Date:	Sat, 4 Dec 2010 15:55:22 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Christoph Lameter <cl@...ux.com>,
	John Stultz <johnstul@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC 1/8] Introduce dynamic clock devices

On Mon, Nov 08, 2010 at 07:38:41AM +0100, Arnd Bergmann wrote:
> On Thursday 04 November 2010, Richard Cochran wrote:
> > +struct clock_device {
> > +	struct file_operations fops;
> > +	struct file_operations *driver_fops;
> > +	struct clock_device_operations *ops;
> > +	struct cdev cdev;
> > +	struct kref kref;
> > +	struct mutex mux;
> > +	void *priv;
> > +	int index;
> > +	bool zombie;
> > +};
> 
> You should really not need the file_operations here, neither the
> struct nor the pointer. Just define a static file_operations
> structure containing clock_device_open and clock_device_release,
> and whatever else you might need, then add the driver's operations
> to clock_device_operations, and pass the clock_device pointer
> directly to them, instead of passing the file/inode pointers.

Arnd, I'm working a revision of this series, and I am not sure I
understand your comment.

The intent here was to allow clock drivers to register a character
device through the clock_device API, since some clocks (hpet, rtc)
already offer a chardev interface.

The same FD from the open character device will also be usable as a
clockid for the generic posix clock_get/settime calls. Thus, the
clock_device layer needs to hook into the file open/release functions.

Are you suggesting that I simply offer all of the functions from a
'struct file_operations' (sans file/inode) in the 'struct
clock_device_operations' too?

I wanted to avoid duplicating the file_operations functions, so that
future changes in those functions would automatically trickle down to
the clock drivers.

Thanks,
Richard

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