netdev - Re: custom ioctl-based interface to control LED in networking (was Re: [PATCHv2 09/10] rfkill: Userspace control for airplane mode)

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Date:	Wed, 24 Feb 2016 14:31:33 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Pavel Machek <pavel@....cz>
Cc:	rpurdie@...ys.net, j.anaszewski@...sung.com,
	linux-leds@...r.kernel.org,
	João Paulo Rechi Vita <jprvita@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Darren Hart <dvhart@...radead.org>,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	platform-driver-x86@...r.kernel.org, linux-api@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux@...lessm.com,
	João Paulo Rechi Vita 
	<jprvita@...lessm.com>
Subject: Re: custom ioctl-based interface to control LED in networking (was
 Re: [PATCHv2 09/10] rfkill: Userspace control for airplane mode)

On Wed, 2016-02-24 at 13:14 +0100, Pavel Machek wrote:
> 
> Why would it need to? It could look at default triggers for the led
> if it really wanted to.

And then it needs to change them; if anything goes wrong error recovery
is practically impossible since the trigger information is lost
forever.

> > I'm sure you'd also not like to see 2**7 triggers implemented in
> > rfkill
> > to cover all the possibilities.
> 
> Are all the possibilities useful? I assumed about 2 are. If you need
> 2**7 of them, LED triggers can have parameters.

It's not my position to decide which combinations some system
integrator or userspace developer might find useful.

Even when we add parameters to a trigger (I don't see a generic way to
do that, but please do enlighten me), you're now ignoring the issue of
the userspace controlled GSM modem...

> > Really what you have here is a concept of "airplane mode", and that
> > concept is specific to the rfkill subsystem. This happens to affect
> > mostly an LED trigger, today, but as a concept it's something that
> > *should* be managed within the rfkill subsystem.
> 
> How is that concept used outside the LEDs? What semantics does
> "airplane mode" have? You tried to explain "airplane mode" is not
> well defined up in this thread...

I'd say it's well-defined for any given set of system software, so if
e.g. NetworkManager decides to define it one way, and connman another
way, there's a definition but the kernel need not interfere with it.

> > > Besides, the series really should have been Cc-ed to LED
> > > people, too.
> > 
> > That's simply unreasonable, you're essentially saying that any user
> > of any kernel infrastructure should be Cc'ed to the implementer of
> > that infrastructure... 9/10 patches in this series aren't even LED
> > specific,
> 
> I'm not saying that. I'm saying that LED maintainers should be Cced,
> to keep the interfaces consistent.

I pretty much have to read it that way, since the LED API is in no way
impacted by these changes. Here's a new trigger, with some magic inner
working. No impact on the LED API.

johannes