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

[Matthias Fend]

Hi Ahmad,

> ________________________________________
> Von: Ahmad Fatoum <a.fatoum at pengutronix.de>
> Gesendet: Donnerstag, 5. November 2020 21:57
> An: Matthias Fend; barebox at lists.infradead.org
> Betreff: Re: [PATCH] Documentation: state: add a little note about modifying a state variable in the frontend
>
> Hello Matthias,
>
> On 11/5/20 9:16 PM, Matthias Fend wrote:
>> Signed-off-by: Matthias Fend <matthias.fend at wolfvision.net>
>> ---
>>   Documentation/user/state.rst | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/Documentation/user/state.rst b/Documentation/user/state.rst
>> index 78ce24f..d9a8e76 100644
>> --- a/Documentation/user/state.rst
>> +++ b/Documentation/user/state.rst
>> @@ -689,4 +689,5 @@ be accessed like normal shell variables. The ``state`` command is used
>>   to save/restore a *state* variable set to the backend device.
>>
>>   After initializing the variable can be accessed with ``$state.foo``.
>> +To modify the value of a state variable use ``nv dev.state.foo=bar``.
>
> 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.

>   - 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.

>
> 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 ;)

Thanks,
  ~Matthias


>
>>   ``state -s`` stores the *state* to the backend device.
>>
>
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