Hi Stefan,
On Tue, 2 Aug 2022 at 07:45, Stefan Herbrechtsmeier stefan.herbrechtsmeier-oss@weidmueller.com wrote:
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@weidmueller.com wrote:
From: Stefan Herbrechtsmeier stefan.herbrechtsmeier@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.
Well if you update that attribute it can change the size of the DTB which is the chicken-and-egg problem again. As far as I know, if people set the size of the region to something a bit larger than needed, the problem is avoided. But the image generation does need to be deterministic.
Do you have a test for this use case?
There are various ones, e.g. testCompressDtb()
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 used in the Chromium OS verified boot implementation, but not elsewhere.
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.
Yes I understand that, however you can pass a parameter to not include the size value.
It would also be possible to add a property to the image (top-level section) that indicates whether this field is present, such property to apply to the whole image. We could have it default to off, if you like.
Regards, Simon