Re: AW: [PATCH] Documentation: state: add a little note about modifying a state variable in the frontend

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Matthias,

On 11/6/20 8:14 AM, Matthias Fend wrote:
>> Von: Ahmad Fatoum <a.fatoum@pengutronix.de>
>>
>> That's wrong. You set the value of a state variable with
>> state.foo=bar. nv dev.state.state.foo=bar uses the _environment_ to
>> save a value to write to state.foo on each boot. This means:
> 
> Thanks for your explanation. Setting a state variable with
> 'state.foo=bar' was actually the way I originally expected.
> Meanwhile, I figured out why I was struggling using things like that.
> All my introduced state variables contained a hyphen in their name.
> And I was not able to set a state variable with 'state.foo-bar=baz' while
> 'nv dev.state.foo-bar=baz' immediately changed the value of
> 'state.foo-bar'. But, as I just learned, with some side effects.
> 
>>
>>   - If you modify the variable from within barebox, it won't be visible
>>     in Linux unless you boot barebox once again.
> 
> I could not verify this behavior. When I change a state variable with
> 'nv dev.state=foo' and then directly boot into Linux (without booting
> barebox again) the 'barebox-state' tool already displays the new value.

Ah, I didn't actually test what I say :D
But makes sense, nv.user sets global.user as well, so why should dev
parameter behave differently.
 
>>   - If you modify the variable from within Linux, nv.dev.state.state.foo
>>     would just overwrite the existing value on the next barebox boot.
> 
> That's true, and of course, not desired.

At least one guess correct ^^

>> Generally, you should only need to modify nv variables at runtime
>> for debugging. nv.dev is meant for stuff like nv.dev.eth0.ethaddr=XX:XX:XX:XX:XX:XX,
>> where you can just hard code a mac address to use, but for state I can't
>> think of any good use cases at the moment.
> 
> Right, state, and also it's frontend, does already what it should do and
> as expected.
> Only the hyphen-obstacle caused troubles. So, maybe there is a trick but the fast fix is to simply
> just avoid names that contain hyphens ;)

v2020.10.0 contains 932481a005cc ("commands: setenv: allow use with hush shell"). You can update/
cherry-pick and then use the setenv command instead out of your hush scripts.

Cheers
Ahmad

> 
> Thanks,
>   ~Matthias
> 
> 
>>
>>>   ``state -s`` stores the *state* to the backend device.
>>>
>>
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Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
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