[RFC PATCH] Provide mechanism for build-time default env entries

[Tom Rini]

On Mon, Jan 20, 2020 at 10:09:21AM -0700, Joel Johnson wrote:
> On 2020-01-20 09:51, Wolfgang Denk wrote:
> > Dear Joel,
> > 
> > In message <20200119073738.29189-1-mrjoel at lixil.net> you wrote:
> > > This enables the building user to specify environment values to be
> > > included in the static default_environment with an image. This is
> > > useful to build multiple otherwise like configured images, varying
> > > by environment unique entries.
> > > 
> > > ---
> > > 
> > > I expected something like this to already be present, but couldn't
> > > find such a mechanism. I also assumed that something similar may
> > > have been proposed previously, but also couldn't find anything via
> > > searching.
> > ...
> > 
> > > +config USER_ENV_SETTINGS
> > > +	string "User build-time additional environment entries"
> > > +	help
> > > +	  This value is reserved for the building user to provide custom
> > > +	  environment entries to be added to the default environment. Care
> > > must
> > > +	  be taken to not break the environment, incompatible entries may
> > > cause
> > > +	  failure to compile, or failure of the target board to properly
> > > +	  initialize or boot. The format is key=value pairs, with entries
> > > +	  separated by C-style escaped null terminated values, such as:
> > > +	    "key1=valueA\0key2=valueB\0key3=valueC".
> > 
> > Something in your descripotion must be missing, or this change makes
> > no sense to me.
> > 
> > >  #ifdef	CONFIG_EXTRA_ENV_SETTINGS
> > >  	CONFIG_EXTRA_ENV_SETTINGS
> > > +#endif
> > > +#ifdef	CONFIG_USER_ENV_SETTINGS
> > > +	CONFIG_USER_ENV_SETTINGS
> > >  #endif
> > 
> > What exactly is the difference between CONFIG_EXTRA_ENV_SETTINGS and
> > CONFIG_USER_ENV_SETTINGS for you, i. e. what can you do with
> > CONFIG_USER_ENV_SETTINGS that cannot be done in exatly the same way
> > with CONFIG_EXTRA_ENV_SETTINGS?
> > 
> > Maybe it would help if you include any code that is actually using
> > this feature?
> > 
> > Best regards,
> > 
> > Wolfgang Denk
> 
> The main different to me is that many boards set/replace
> CONFIG_EXTRA_ENV_SETTINGS, making it unusable as a user build-time
> configuration value. As a result, I can actually specify values for
> CONFIG_USER_ENV_SETTINGS and have them included in the resulting environment
> instead of overridden by the board configuration.
> 
> There is intentionally no code using this feature, as meant in the
> description it is intended to be reserved for the building user's usage. The
> specific use case for which I'm using it is to ease building of multiple
> otherwise identical images, embedding a fixed and well known set of ethernet
> MAC addresses into each unique image for execution in environments with no
> environment storage. It is meant to be used for any other values changed or
> added in the default image environment though - if there is a better way to
> accomplish this I'd be all for it, but I couldn't find anything, thus the
> RFC patch.

I think part of the problem is that CONFIG_EXTRA_ENV_SETTINGS needs to
be migrated to Kconfig.  And that in turn shows that some amount of
things need to be taken out of the CONFIG namespace and moved in to
distinct headers to be included / keyed-in-to.  What we have in
include/environment/ti/ is a start to that but far from complete.

-- 
Tom
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