[PATCH] env: Add option to only ever append environment

[Tom Rini]

On Tue, Jun 02, 2020 at 02:09:57PM +0200, Marek Vasut wrote:
> On 6/2/20 2:05 PM, Rasmus Villemoes wrote:
> > On 02/06/2020 13.04, Marek Vasut wrote:
> >> On 6/2/20 8:42 AM, Rasmus Villemoes wrote:
> >>> On 29/05/2020 19.54, Marek Vasut wrote:
> >>>> +config ENV_APPEND
> >>>> +	bool "Always append the environment with new data"
> >>>> +	default n
> >>>> +	help
> >>>> +	  If defined, the environment hash table is only ever appended with new
> >>>> +	  data, but the existing hash table can never be dropped and reloaded
> >>>> +	  with newly imported data. This may be used in combination with static
> >>>> +	  flags to e.g. to protect variables which must not be modified.
> >>>> +
> >>>>  config ENV_ACCESS_IGNORE_FORCE
> >>>>  	bool "Block forced environment operations"
> >>>>  	default n
> >>>> diff --git a/env/env.c b/env/env.c
> >>>> index 024d36fdbe..967a9d36d7 100644
> >>>> --- a/env/env.c
> >>>> +++ b/env/env.c
> >>>> @@ -204,7 +204,9 @@ int env_load(void)
> >>>>  		ret = drv->load();
> >>>>  		if (!ret) {
> >>>>  			printf("OK\n");
> >>>> +#if !CONFIG_IS_ENABLED(ENV_APPEND)
> >>>>  			return 0;
> >>>> +#endif
> >>>
> >>> Don't use CONFIG_IS_ENABLED() unless you actually introduce both
> >>> CONFIG_FOO and CONFIG_SPL_FOO. Otherwise the above
> >>> CONFIG_IS_ENABLED(ENV_APPEND) is guaranteed to evaluate to false in SPL.
> >>> Of course that only matters if environment support is enabled in SPL,
> >>> but some actually use that.
> >>
> >> We actually want to use CONFIG_IS_ENABLED() as much as possible to make
> >> these options future-proof, so that others won't have to chase down all
> >> kinds of #ifdef CONFIG stuff and fix it later on for SPL/TPL/etc.
> >>
> > 
> > That makes no sense. You're introducing something whose help text
> > doesn't spell out that the option only applies to U-Boot proper, and is
> > completely ignored in SPL (since CONFIG_SPL_ENV_APPEND never exists).
> 
> Anything which does not explicitly spell _SPL or _TPL is U-Boot only,
> except for some remaining options which need fixing.

No, it's not true that every option in Kconfig needs to be listed in
triplicate.

> > The reason it's ignored in SPL is that you use the SPL-or-not-SPL-aware
> > CONFIG_IS_ENABLED() helper, and you say that's so that somebody in the
> > future can implement CONFIG_SPL_ENV_APPEND?
> 
> Yes, because you might need to differentiate between the env behavior in
> TPL/SPL/U-Boot.

I'm not sure it's valid to say that env can behave different (outside
specific cases like readonly before full U-Boot).

> > If you intend for ENV_APPEND to be something that's either set or not
> > set for a given board, then the code needs to use the SPL-agnostic
> > IS_ENABLED(CONFIG_ENV_APPEND). If you intend it to be something that can
> > be set independently for the env support in SPL vs U-Boot proper, you
> > need to add both config options and, as you do, use CONFIG_IS_ENABLED.
> 
> I don't have a way to test it in SPL, so I'm not adding untested config
> options.

Then you should default to making SPL behave the same way as full
U-Boot.

-- 
Tom
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