Re: [Buildroot] [RFC PATCH 1/2] support/scripts/genimage.sh: support creating a bmap image

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

On Tue, 27 Aug 2024 20:55:00 +0200
Peter Korsgaard <peter@korsgaard.com> wrote:

> Sorry for the slow response, I only got to this now while backporting
> for LTS, but I don't like the fact that it hardcodes gzip compression
> (with a specific compression level), especially as it is
> hidden/optionless now, E.G. it seems quite random that if you have a
> genimage.cfg creating a sdcard.img (or whatever) and you then enable
> host-bmaptools you all of a sudden don't have sdcard.img anymore, but
> sdcard.img.gz (and sdcard.img.bmap) and "waste" time doing the
> compression you may or may not want.
> 
> I would suggest to drop the gzip step and only create the .bmap files
> (which presumably is quite fast?)
> 
> What do you say?

I understand your concern, but compression is also what helps in making
those sparse images small. Of course, as long as you keep them where
Buildroot generated them, they are sparse, so they don't take much
space. But as soon as you "distribute" them, they usually loose their
sparse-ness, and this is where compressing the image + the bmap
metadata file helps in lot in reducing the amount of data.

But fair enough, I assume this compression can be done as a custom
post-processing step by whoever needs it.

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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