[U-Boot] [RFC PATCH] u-boot: remove driver lookup loop from env_save()

[Maxime Ripard <maxime.ripard@bootlin.com>]

On Thu, Jul 12, 2018 at 09:02:26AM +0200, Simon Goldschmidt wrote:
> 
> 
> On 11.07.2018 15:50, Maxime Ripard wrote:
> > On Wed, Jul 11, 2018 at 12:44:23PM +0200, Nicholas wrote:
> > > > > > Maybe a solution could be to have an env_save() function which
> > > > > > acts in a similar way as proposed in my patch and an
> > > > > > env_save_prio() function, which acts like the env_load()
> > > > > > i.e. looking for the best working location instead of relying
> > > > > > on what has been stored into gd-> env_load_location.
> > > > > 
> > > > > I don't really see a use-case for overriding wherever the
> > > > > environment at the user-level actually. At the board level, for
> > > > > redundancy or transition, yes, definitely, but we can already do
> > > > > that.
> > > > 
> > > > Well, the use case I saw was that I wanted to test redundant
> > > > environment  storage. I admit this is not an end user use case but
> > > > a developer use  case, so I guess you're right.
> > > > 
> > > > So after fixing this endless loops I see two questions: - to which
> > > > environment do we store if the one in 'env_load_location'  fails
> > > > to store?
> > > 
> > > Good question. My opinion is that it strongly depends on what we want
> > > to achieve with the implementation: do we want 1) to keep the
> > > consistency between load and save, or we want 2) to guarantee to be
> > > able to load/save from at least one location?
> > > 
> > > If 1) then a failure on env_save() simply fails and doesn't store
> > > anything. In other words we are multi-env when loading but single-env
> > > when storing. We are actually binding env_save() to the last
> > > env_load()'s result.
> > > 
> > > If 2) then a failure on env_save() will try all the available locations
> > > but we are open to misalignments. Here we are full multi-env since
> > > env_save() and env_load() are not bound together.
> > 
> > In that case, we don't want to store to a lower priority, but to a
> > higher one. Otherwise, the environment will be saved just fine, but
> > will not be read next time, which will be very confusing to the user.
> > 
> > And with a higher priority, you might end up overwriting something you
> > weren't expecting to overwrite, so I'd vote 1.
> 
> I agree that 1 would be best. But from reading the code, unless I'm totally
> wrong, it seems that the patch sent by Nicholas does not suffice:
> 
> If no location contained a valid environment (e.g. no environment written
> yet), the lowest priority will be written as 'gd->env_load_location' is set
> to the lowest priority from iterating locations in 'env_load()'.
> 
> So we might have to reset 'gd->env_load_location' to highest prio if loading
> the environment fails.

That would make sense yes.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com
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