[U-Boot] [RFC PATCH v2] u-boot: remove driver lookup loop from env_save()

[Nicholas]

On gio, 2018-07-12 at 13:02 +0200, Simon Goldschmidt wrote:
> 
> On 12.07.2018 12:52, Nicholas Faustini wrote:
> > 
> > When called with ENVOP_SAVE, env_get_location() only returns the
> > gd->env_load_location variable without actually checking for
> > the environment location and priority.
> > 
> > This behaviour causes env_save() to fall into an infinite loop when
> > the low-level drv->save() call fails.
> > 
> > The env_save() function should not loop through the environment
> > location list but it should save the environment into the location
> > stored in gd->env_load_location by the last env_load() call.
> > 
> > Signed-off-by: Nicholas Faustini <nicholas.faustini at azcomtech.com>
> > ---
> > 
> > Changes in v2:
> > - Restore gd->env_load_location to the highest priority location
> > when
> >    env_load() fails
> > 
> >   env/env.c | 10 ++++++----
> >   1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/env/env.c b/env/env.c
> > index 5c0842a..18eb78d 100644
> > --- a/env/env.c
> > +++ b/env/env.c
> > @@ -205,22 +205,24 @@ int env_load(void)
> >   			return 0;
> >   	}
> >   
> > +	env_get_location(ENVOP_LOAD, 0);
> A comment why this is required would be good, I guess.
Sure, I thought the same but eventually I didn't put it. Will do in the
next version.
> 
> > 
> > +
> >   	return -ENODEV;
> >   }
> >   
> >   int env_save(void)
> >   {
> >   	struct env_driver *drv;
> > -	int prio;
> >   
> > -	for (prio = 0; (drv = env_driver_lookup(ENVOP_SAVE,
> > prio)); prio++) {
> > +	drv = env_driver_lookup(ENVOP_SAVE, 0);
> Thinking again about this, would it make more sense to store 
> 'env_load_prio' in 'gd' after successful load? That way, 
> 'env_get_location()' would be more straightforward (no special case
> for 
> ENVOP_SAVE) and here in 'env_save()' we could just write something
> like 
> this:
> 
> drv = env_driver_lookup(ENVOP_SAVE, gd->env_load_prio);
> 
> 
I really like the 'env_load_prio' idea. But I also like having the
special case for ENVOP_SAVE in env_get_location() as it enforces the
fact that the location of 'save' is bound to the location of previous
'load'.
I however don't have a strong opinion on this. I could even remove the
whole switch() statement if we introduce 'env_load_prio'.

Also, I have some doubts about what it should be returned when !drv-
>save and !env_has_inited(drv->location) (below)... I put -ENODEV but I
don't like it so much.

> Simon
> 
> > 
> > +	if (drv) {
> >   		int ret;
> >   
> >   		if (!drv->save)
> > -			continue;
> > +			return -ENODEV;
> >   
> >   		if (!env_has_inited(drv->location))
> > -			continue;
> > +			return -ENODEV;
> >   
> >   		printf("Saving Environment to %s... ", drv-
> > >name);
> >   		ret = drv->save();
> >