Re: [PATCH 3/4] fdtfactor: Support compressed DTB inputs and outputs

[David Gibson]

On Thu, Oct 15, 2026 at 11:21:36AM -0700, Douglas Anderson wrote:
> Firmware and FIT image build pipelines frequently store device tree
> blobs compressed with LZ4, LZMA/XZ, or gzip (e.g., `.dtb.lz4`).
> 
> Extend `fdtfactor` to detect compressed input blobs by magic bytes or
> file extension, transparently decompress them before factoring, and
> compress the resulting `.dtbo` and `base.dtb` outputs when appropriate:
> 
> - Support `.lz4` (via the `lz4` CLI), `.lzma`/`.xz` (via Python's
>   `lzma` module), and `.gz` (via Python's `gzip` module).
> - Preserve the input compression format on generated `.dtbo` files and
>   compress `base.dtb` when its output path carries a compression suffix
>   (e.g., `-b base.dtb.lz4`).
> - Report compressed size savings alongside uncompressed savings when
>   `-v`/`--verbose` is specified.
> 
> On the 47 Qualcomm SC7180 Trogdor Chromebook `.dtb.lz4` files,
> `fdtfactor -S` reduces total LZ4-compressed size from 1.71 MB to 213 KB
> (87.5% savings).

I'm not going to review patches 3 & 4 at this time.  Patch 2 will need
a bunch of rework before it's ready, which will necessarily require
substantial changes to the following patches as well.  So, I'll defer
considering these until (at least) the next spin.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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