Re: [PATCH v5 07/12] PM / devfreq: export devfreq_class

[Matthias Kaehlcke]

Hi,

On Wed, Jul 04, 2018 at 02:30:32PM +0900, Chanwoo Choi wrote:

> I didn't see any framework which exporting the class instance.
> It is very dangerous. Unknown device drivers is able to reset
> the 'devfreq_class' instance. I can't agree this approach.

While I agree that it is potential dangerous it is actually a common
practice to export the class:

grep "extern struct class " include/linux/ -R
include/linux/rio.h:extern struct class rio_mport_class;
include/linux/tty.h:extern struct class *tty_class;
include/linux/fb.h:extern struct class *fb_class;
include/linux/ide.h:extern struct class *ide_port_class;
include/linux/device.h:extern struct class * __must_check __class_create(struct module *owner,
include/linux/devfreq.h:extern struct class *devfreq_class;
include/linux/switchtec.h:extern struct class *switchtec_class;
include/linux/input.h:extern struct class input_class;
include/linux/genhd.h:extern struct class block_class;
include/linux/power_supply.h:extern struct class *power_supply_class;
include/linux/rtc.h:extern struct class *rtc_class;

struct class_interface and class_interface_register() would be
pointless without exported classes.

My understanding is that the kernel is often lax on encapsulation and
exposes private/delicate data pragmatically within the kernel when
needed because "the kernel trusts itself".

Thanks

Matthias