linux-kernel - setting brightness as privileged operation?

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Message-ID: <20170105092307.GD21618@dhcp22.suse.cz>
Date:   Thu, 5 Jan 2017 10:23:07 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Jingoo Han <jingoohan1@...il.com>, Lee Jones <lee.jones@...aro.org>
Cc:     linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: setting brightness as privileged operation?

Hi,
I have just learned that my Xfce Power Manager cannot manipulate
brightness because I do not have policykit installed on my computer.
There is a reason for that (yeah it depends on systemd which I prefer
not have).

While this is clearly a problem of the Xfce applet I am wondering why
setting the brightness has to be a privileged operation at all. Is there
any strong reason for it or just a general policy that we do not give
world writable files into sysfs?
-- 
Michal Hocko
SUSE Labs