[U-Boot] [RFC] env: Fix errors printing on env loading

[Wolfgang Denk]

Dear Sam,

In message <20180718213736.22650-1-semen.protsenko at linaro.org> you wrote:
> This is just a draft to discuss ideas related to "Make U-Boot log great
> again" thread.
>
> With this patch we will have something like this:
>
>     Attempting to load environment from FAT:
>     MMC: no card present
>     ** Bad device mmc 0 **
>     Failed (-5)
>     Attempting to load environment from MMC: OK
>
> instead of this:
>
>     Loading Environment from FAT... MMC: no card present
>     ** Bad device mmc 0 **
>     Failed (-5)
>     Loading Environment from MMC... OK

The new output is worse, as it consumes even more lines of output.

> The only way I see to do so is to use ASCII escape codes for moving the
> cursor (in non-error case).

NAK!!!  Please keep in mind that output usually goes to a serial
port, and should not assume any speific "terminal" capabilities.
Even simple in-line "editing" like "overprinting by outputting
backspace characters causes a LOT of hassle when you try to parse
output for example in automatic test suites.

Adding more complex terminal control or other fancy stuff (like
colors etc) is a _strict_ no, no!

> I'd also like to add prefixes to error messages, like it's done in [2],
> but it requires adding one pointer to global data struct.

As I explained befoire, this has a lot of negative consequences.
You think about beauty, but please keep functionality and efficiency
(boot time) in mind!

Best regards,

Wolfgang Denk

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