Add support for android boot by alexlarsson · Pull Request #399 · composefs/composefs-rs

alexlarsson · 2026-09-23T14:49:18Z

This is some preparatory work for bootc support for android boot. It has two parts:

basic parsing of android boot v2 images, comparable to the existing uki parser
Add BootEntry::Aboot picking up aboot boot artifacts from the image.

This is the branch used in the pr: composefs/composefs-rs#399 This change is temporary, and we should replace it with a released version.

This is the branch used in the pr: composefs/composefs-rs#399 This change is temporary, and we should replace it with a released version. Signed-off-by: Alexander Larsson <alexl@redhat.com>

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🟡 Changes recommended

Untrusted component sizes can cause excessive allocation, and module-directory discovery lacks tests.

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Review effort: Balanced
Findings: 1 · 2

Open (3)

Validate component range before allocating · New
Correct Android boot image format wording · New
Add coverage for module-directory payload discovery · New

What changed in this PR

Adds preparatory Android boot v2 parsing and aboot artifact discovery.

Changes:

Parses Android boot v2 headers, components, and command lines.
Discovers Android/UKI aboot payloads and matching vbmeta files.
Adds BootEntry::Aboot, while explicitly rejecting unsupported writes.

File	Description
`android_boot.rs`	Implements Android boot v2 parsing and tests.
`bootloader.rs`	Discovers and validates aboot artifacts.
`lib.rs`	Exposes the Android boot module.
`uki.rs`	Adds a shared UKI test fixture.
`write_boot.rs`	Rejects unsupported aboot writing.

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We'll need this later to parse aboot boot data. Signed-off-by: Alexander Larsson <alexl@redhat.com>

This looks for aboot.img and optional vbmeta.img for android boot support. Signed-off-by: Alexander Larsson <alexl@redhat.com>

alexlarsson · 2026-09-28T15:05:02Z

@cgwalters This changes the API a bit, so it kinda naturally breaks the reverse dependency. How do we handle this?

cgwalters · 2026-09-28T15:09:44Z

The reverse dependency CI is intentionally not a gating test, but yes SOP is currently to do one of

disable it and then re-enable it when an updated bootc has landed
point it at your fork's draft of an update for this, re-point to main once update has landed

And we need some kind of automatic reminder on this

alexlarsson · 2026-09-28T15:14:56Z

@cgwalters lemme disable it for now then

This changes some APIs, and we need the corresponding changes in bootc from: bootc-dev/bootc#2490 We'll re-enable this once that is merged. Signed-off-by: Alexander Larsson <alexl@redhat.com>

cgwalters

Nothing blocking

cgwalters · 2026-09-28T15:29:55Z

 jobs:
  bootc-test:
    name: Build and test bootc with local composefs-rs
+    if: never()


For followup This should really have a TODO comment... I guess what we really need is like a cargo xtask style script that handles this, then we could even have a CI check there that causes a nonblocking CI failure e.g. a month later to ensure we don't forget to re-enable it

cgwalters · 2026-09-28T15:30:17Z

+// Layout from Android's boot image specification:
+// https://android.googlesource.com/platform/system/tools/mkbootimg/+/refs/heads/main/include/bootimg/bootimg.h
+#[derive(Debug, FromBytes, Immutable, KnownLayout)]
+#[cfg_attr(test, derive(zerocopy::IntoBytes))]


So much nicer w/zerocopy right?

cgwalters · 2026-09-28T15:32:46Z

+        let end = nul_terminated_len(&self.cmdline);
+        Ok(std::str::from_utf8(&self.cmdline[..end])?)


I think this would be a lot cleaner using

https://doc.rust-lang.org/stable/std/ffi/struct.CStr.html#method.from_bytes_with_nul + str::from_utf8 on the bytes from that CStr

In fact standing rule we should have in our Rust style guide:

In Rust, most cases of array indexing can be replaced with methods that have better runtime safety and avoid implicit panics; this is one. Using str::split_once is another great example

This is in #405

This is the branch used in the pr: composefs/composefs-rs#399 This change is temporary, and we should replace it with a released version. Signed-off-by: Alexander Larsson <alexl@redhat.com>

alexlarsson added a commit to alexlarsson/bootc that referenced this pull request Sep 23, 2026

WIP: Use a composefs-rs from aboot-support branch

ca4eb8d

This is the branch used in the pr: composefs/composefs-rs#399 This change is temporary, and we should replace it with a released version.

alexlarsson force-pushed the aboot-support branch from cbf4e98 to d879e41 Compare September 23, 2026 15:02

alexlarsson mentioned this pull request Sep 23, 2026

composefs: Add support for android boot (both regular and ukiboot) bootc-dev/bootc#2490

Open

cgwalters reviewed Sep 23, 2026

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Comment thread crates/composefs-boot/src/bootloader.rs Outdated

Comment thread crates/composefs-boot/src/bootloader.rs

alexlarsson force-pushed the aboot-support branch from d879e41 to 62e7cb8 Compare September 24, 2026 13:46

cgwalters previously approved these changes Sep 25, 2026

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cgwalters requested a balanced review from Copilot September 25, 2026 16:31

Copilot started reviewing on behalf of cgwalters September 25, 2026 16:32 View session

Copilot AI reviewed Sep 25, 2026

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Comment thread crates/composefs-boot/src/android_boot.rs

Comment thread crates/composefs-boot/src/android_boot.rs Outdated

Comment thread crates/composefs-boot/src/bootloader.rs

alexlarsson dismissed cgwalters’s stale review via 9d0af7d September 28, 2026 09:25

alexlarsson force-pushed the aboot-support branch from 62e7cb8 to 9d0af7d Compare September 28, 2026 09:25

alexlarsson added 2 commits September 28, 2026 15:36

Add Android Boot v2 image parser

235f25b

We'll need this later to parse aboot boot data. Signed-off-by: Alexander Larsson <alexl@redhat.com>

Add android boot boot resources

fdc9e10

This looks for aboot.img and optional vbmeta.img for android boot support. Signed-off-by: Alexander Larsson <alexl@redhat.com>

alexlarsson force-pushed the aboot-support branch from 9d0af7d to fdc9e10 Compare September 28, 2026 13:37

CI: Temporarily disable bootc reverse dependency CI

d462240

This changes some APIs, and we need the corresponding changes in bootc from: bootc-dev/bootc#2490 We'll re-enable this once that is merged. Signed-off-by: Alexander Larsson <alexl@redhat.com>

cgwalters approved these changes Sep 28, 2026

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alexlarsson enabled auto-merge September 28, 2026 16:02

alexlarsson added this pull request to the merge queue Sep 28, 2026

Merged via the queue into main with commit b90ef51 Sep 28, 2026
29 of 31 checks passed

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Add support for android boot - #399

Add support for android boot#399
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		let end = nul_terminated_len(&self.cmdline);
		Ok(std::str::from_utf8(&self.cmdline[..end])?)

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