Bug#1032610: reliably composable initramfs - zero-pad output to allow concatenation

From	Birgit Edel <edelbitter@posteo.de>
Newsgroups	linux.debian.bugs.dist, linux.debian.kernel
Subject	Bug#1032610: reliably composable initramfs - zero-pad output to allow concatenation
Date	2025-11-17 14:20 +0100
Message-ID	<LS7jc-dDNX-25@gated-at.bofh.it> (permalink)
References	<G7Ad3-bnVa-3@gated-at.bofh.it> <LRUlX-dvbI-11@gated-at.bofh.it> <G7Ad3-bnVa-3@gated-at.bofh.it> <LRUlX-dvbI-11@gated-at.bofh.it>
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Cross-posted to 2 groups.

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> you want mkinitramfs to support multiple compressed parts

I would caution against that and rather only add the quick and easy bit:

1) Fixing the regression and adding autopkgtest is adds little code yet
solves the hassle for any *manual* workflow that once worked.

2) Actually parsing such archives is way more complicated - and for 
what? Unless
unmkinitramfs was aiming for perfect bug-compatibility with kernel code 
it would
always harbor potential for dangerously misleading output.

> whether 3cpio supports multiple compressed parts

No. Looks like it shuts down even if current decompression stopped short 
of EOF:
https://github.com/bdrung/3cpio/blob/2ffd9dc9ce46f5d885fb066eef73b127889918e2/src/examine.rs#L85
https://github.com/bdrung/3cpio/blob/2ffd9dc9ce46f5d885fb066eef73b127889918e2/src/extract.rs#L181
(Still good, insofar it means my suggested unconditional padding does 
not make it crash.)

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Bug#1032610: reliably composable initramfs - zero-pad output to allow concatenation Ben Hutchings <ben@decadent.org.uk> - 2025-11-17 00:30 +0100
  Bug#1032610: reliably composable initramfs - zero-pad output to allow concatenation Birgit Edel <edelbitter@posteo.de> - 2025-11-17 14:20 +0100

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