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

[Sascha Hauer]

On Fri, Nov 06, 2020 at 07:14:09AM +0000, Matthias Fend wrote:
> 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 ;)

How about converting the hyphens to underscores for the variable names
(I mean in code, not in your dts files)?

Sascha

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