[PATCH 2/3] binman: Remove header from compressed data

[Stefan Herbrechtsmeier]

Hi Simon,

Am 02.08.2022 um 14:41 schrieb Simon Glass:
> Hi Stefan,
> 
> On Tue, 2 Aug 2022 at 06:29, Stefan Herbrechtsmeier
> <stefan.herbrechtsmeier-oss at weidmueller.com> wrote:
>>
>> From: Stefan Herbrechtsmeier <stefan.herbrechtsmeier at weidmueller.com>
>>
>> Remove header from compressed data because this is uncommon, not
>> supported by U-Boot and incompatible with external compressed artifacts.
>>
>> The header was introduced as part of commit eb0f4a4cb402 ("binman:
>> Support replacing data in a cbfs") to allow device tree entries to be
>> larger that the compressed contents. Regarding the commit "this is
>> necessary to cope with a compressed device tree being updated in such a
>> way that it shrinks after the entry size is already set (an obscure
>> case)". This case need to be fixed without influence the compressed data
>> by itself.
> 
> I was not able to find a way around this due to the chicken-and egg
> problem. Compressed data has an unpredictable size and adding an extra
> uncompressed byte may increase or decrease the compressed size.

Is it possible to use the `pad-after` attribute to record the unused 
space. In this case it is possible to calculate the size of the 
compressed data.

Do you have a test for this use case?

> So my solution was to add the header.

Is the header used outside of binman? I don't spot it in the decompress 
fitImage implementation.


> It is optional though, so can we perhaps have a property in the
> description to enable it?

Is this header needed and supported outside of binman?

At the moment the header is incompatible and not well documented. It 
took me some time to find out why my gzip compression via binman doesn't 
work as expected because I assume a compatibility between binman 
compress and fitImage decompress.

Regards
   Stefan