Re: [PATCH] rfkill: create useful userspace interface

[Alan Jenkins <alan-jenkins@tuffmail.co.uk>]

Marcel Holtmann wrote:
> Hi Johannes,
>
>   
>> Would everybody be happy with this rolled in?
>>
>> johannes
>>
>> Subject: rfkill: userspace API improvements
>>
>> This adds the two following things to /dev/rfkill:
>>  1) notification to userspace with a new operation
>>     RFKILL_OP_NVS_REPORT about default states restored
>>     from platform non-volatile storage
>>     
>
> I really don't understand why this is needed. What benefit does it give
> us compared to just sent OP_CHANGE and OP_CHANGE as an update. My X200
> for example does this anyway on suspend/resume.
>   

This is required for boot only.  I have no reason for this event to be 
generated on resume.

The same effect could be had by generating an OP_CHANGE on f_open, 
_only_ when a platform driver has provided a value from NVS.  But it 
does seem clearer to make it a different type of event.

> So what is rfkilld suppose to be doing when receiving this report? What
> is the expected behavior? Why do we bother with multi-OS crap here? I am
> really unclear what are we trying to solve here.
>   

In order to replicate the kernel behavior, it is expected that you set 
your internal state from this event.  E.g. when the user next presses 
the wireless toggle key, you set the inverse of that internal state.

Since this event is generated by a platform driver, you can expect it to 
be present following coldplug (the udev initscript).  If the event is 
not present after coldplug, you may then issue OP_CHANGE yourself, to 
e.g. restore the state from a file.  You would not be expected to handle 
OP_NVS_REPORT after startup.  (Unless the daemon is restarted).

Replicating the kernel behavior will allow us to avoid causing a couple 
of niggly little regressions on at least two platforms.  It preserves 
the behavior when dual-booting (possibly between different linux 
distros), and when the BIOS setup screen exposes the NVS state as an 
option.  The new behavior you suggest will annoy any users who have 
become used to these scenarios "just working". 

You may not use these platforms yourself.  But I'm as annoyed as 
Henrique is, we don't want to impose regressions just because other 
platforms don't implement the feature.

Why the fuss about implementing this, it seems easy enough?  Start 
rfkilld after udev (like everything else).  If you get NVS_REPORT, then 
use those states.  Fill in any other states from defaults or state files 
and issue OP_CHANGE for them, just as you're already planning.  Ignore 
any subsequent NVS_REPORTs.  That should cover it.

It's the cost for starting from a working implementation.  You benefit 
from having existing drivers and users, you pay by not breaking them 
without good reason.

Thanks
Alan