[Sugar-devel] More details on brightness control in Sugar

Martin Abente martin.abente.lahaye at gmail.com
Fri May 8 15:26:42 EDT 2015

Hello Sam and James,

I have sent a PR for the complete work on brightness controls for Sugar
[1]. Please give it a try!


1. https://github.com/sugarlabs/sugar/pull/504

On Wed, May 6, 2015 at 2:18 PM, Martin Abente <
martin.abente.lahaye at gmail.com> wrote:

> Alright, working on it already ;) Should have something to show today.
> On Wed, May 6, 2015 at 5:31 AM, Sam P. <sam.parkinson3 at gmail.com> wrote:
>> Hi Martin,
>> Using the sugar-backlight-helper with a polkit file to change the
>> brightness file sounds like a very good idea.  That would significantly
>> reduce the complexity of the change.
>> Please feel free to make the changes and send through a patch.
>> I will try and fix up the iconography issues.
>> Thanks,
>> Sam
>> On Wed, May 6, 2015 at 9:43 AM James Cameron <quozl at laptop.org> wrote:
>>> Thanks for the research.
>>> On Tue, May 05, 2015 at 06:27:59PM -0400, Martin Abente wrote:
>>> > [...]
>>> > It would not be too difficult to re-implement the same mechanism for
>>> > Sugar. In fact I have re-implemented the exact same functionality
>>> > provided by "gsd-backlight-helper" in
>>> > Python.  https://github.com/tchx84/
>>> > sugar-backlight-helper/blob/master/sugar-backlight-helper.py
>>> Have to remove .py from the link.
>>> > @James, can you also give it a try?
>>> Worked fine for me on Ubuntu 14.04.2 on commodity hardware.  Small
>>> changes to README.md sent in pull request.
>>> > (this also works for the XO btw).
>>> Yes, and it will be useful for integration with the proposed frame
>>> device icon for the display.
>>> The F9 and F10 keys will continue to be intercepted by olpc-kbdshim.c,
>>> which calls olpc-brightness shell script in subprocess.
>>> However, a similar user experience with the audio device icon will
>>> occur, where the Sugar UI will ignore changes made by olpc-brightness.
>>> See #1677 and dev.laptop.org #9913.
>>> So Sugar will need a way to be informed of brightness changes made by
>>> other processes; which on commodity hardware will be brightness
>>> controls handled by other system programs, and on XO laptops will be
>>> olpc-kbdshim and powerd.
>>> To detect changes to a sysfs file; not sure how this is done, but for
>>> the time being we can read it occasionally.  To make that more
>>> efficient, I've added --get-path option to the helper.  See pull
>>> request #2.
>>> > Regarding the use of a separate tool to deal with permissions, I
>>> > wonder if GSD deliberately separated that tool to simplify the
>>> > integration with PolKit. The question is: should we do something
>>> > similar with sugar? I personally think is a valid option, but I
>>> > wonder if there is another way of using PolKit to grant permissions
>>> > directly to Sugar for writing to the device. I don't have much
>>> > experience with PolKit.
>>> Security design is that the program that needs the secure access
>>> should be as small as possible.
>>> Otherwise, you widen the attack vector to everything in Sugar shell.
>>> > @Sam, @James, if we think we can go this direction, I can will some
>>> > changes on top of Sam's previous work tomorrow.
>>> Adding sugar-backlight-helper to the sugar sources seems to be the
>>> right direction.  This adds a dependency on polkit, but you could make
>>> it a soft dependency and not install the helper if polkit is not
>>> available.
>>> --
>>> James Cameron
>>> http://quozl.linux.org.au/
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