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

[Tom Rini <trini@konsulko.com>]

On Tue, Jun 02, 2020 at 05:55:25PM +0200, Marek Vasut wrote:
> On 6/2/20 4:38 PM, Tom Rini wrote:
> > On Tue, Jun 02, 2020 at 02:47:12PM +0200, Marek Vasut wrote:
> >> On 6/2/20 2:44 PM, Tom Rini wrote:
> >>> On Tue, Jun 02, 2020 at 02:05:39PM +0200, 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).
> >>>> 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?
> >>>>
> >>>> 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.
> >>>
> >>> How will this code behave if there is a mismatch between SPL and full
> >>> U-Boot (disabled SPL, enabled full, as the patch stands today) ?
> >>
> >> One will append the environment, the other will override it (if you have
> >> multiple envs enabled).
> > 
> > So it sounds like it wouldn't be valid to have this option differ
> > between SPL and main U-Boot?
> 
> Consider the case where you have default env in SPL, and multiple envs
> in U-Boot proper.

Yes, today you can end up with cases where you build something that doesn't
work as intended (likely something around falcon boot and/or boot count
limit in env).  Which is what I'm getting at here.  Is there some
cases where it would make any sense to enable this option in full U-Boot
but disable it in SPL?

-- 
Tom
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