[WIP] vhdx: add pure-Rust VHDX parser and disk layer

[jstarks]

Add a pure-Rust VHDX implementation with full read/write support, write-ahead logging, crash consistency, free space management, trim, differencing disk chains, and a disk_backend integration layer.

This allows non-Windows hosts to use VHDX files.

[github-actions]

⚠️ Unsafe Code Detected

This PR modifies files containing unsafe Rust code. Extra scrutiny is required during review.

For more on why we check whole files, instead of just diffs, check out the Rustonomicon

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a cross-platform, pure-Rust VHDX implementation (parser + read/write + WAL pipeline) and wires it into OpenVMM’s layered disk stack so .vhdx works without the Windows-only kernel driver.

Changes:

• Introduces a new vhdx crate with VHDX format parsing, metadata/region/header handling, and a WAL-backed commit/apply pipeline.
• Adds a new disklayer_vhdx crate implementing LayerIo + resolver, including parent-locator chain walking.
• Updates OpenVMM resource registration and disk-opening logic to use the new VHDX backend for .vhdx.

Reviewed changes

Copilot reviewed 34 out of 41 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
vm/devices/storage/vhdx/src/sector_bitmap.rs	Sector bitmap cache + partially-present read resolution; adds unit tests.
vm/devices/storage/vhdx/src/region.rs	Region table parsing/validation + rewrite via WAL; adds tests.
vm/devices/storage/vhdx/src/metadata.rs	Metadata table parsing + item reads; adds tests.
vm/devices/storage/vhdx/src/lsn_watermark.rs	Async LSN/FSN watermark primitive with poisoning + tests.
vm/devices/storage/vhdx/src/log_task.rs	WAL logging task plumbing and tail advancement + tests.
vm/devices/storage/vhdx/src/log_permits.rs	Failable semaphore for pipeline backpressure + tests.
vm/devices/storage/vhdx/src/locator.rs	Parent locator parsing (UTF-16 KV table) + tests.
vm/devices/storage/vhdx/src/lib.rs	Crate root + module exports + AsyncFile trait.
vm/devices/storage/vhdx/src/known_meta.rs	Parses well-known metadata items + required-item validation + tests.
vm/devices/storage/vhdx/src/header.rs	Dual-header parsing + serialized header updates + tests.
vm/devices/storage/vhdx/src/format.rs	On-disk structs/constants + checksums + GUIDs + layout tests.
vm/devices/storage/vhdx/src/flush.rs	Flush sequencer implementation + tests.
vm/devices/storage/vhdx/src/error.rs	Error and corruption enums used across the crate.
vm/devices/storage/vhdx/src/create.rs	VHDX creation logic (headers/regions/metadata/BAT) + tests.
vm/devices/storage/vhdx/src/apply_task.rs	Apply task writing logged pages to final offsets.
vm/devices/storage/vhdx/Cargo.toml	Defines the new vhdx crate and dependencies.
vm/devices/storage/disklayer_vhdx/src/resolver.rs	Resource resolver for VhdxDiskLayerHandle.
vm/devices/storage/disklayer_vhdx/src/lib.rs	LayerIo implementation bridging vhdx ranges to buffers.
vm/devices/storage/disklayer_vhdx/src/io.rs	BlockingFile implementing vhdx::AsyncFile via blocking pool.
vm/devices/storage/disklayer_vhdx/src/chain.rs	Helpers to open single VHDX or auto-walk differencing chains.
vm/devices/storage/disklayer_vhdx/Cargo.toml	Defines the new disklayer crate + deps/tests.
vm/devices/storage/disk_backend_resources/src/layer.rs	Adds VhdxDiskLayerHandle resource type.
openvmm/openvmm_resources/src/lib.rs	Registers the new VHDX disklayer resolver.
openvmm/openvmm_resources/Cargo.toml	Adds disklayer_vhdx dependency.
openvmm/openvmm_helpers/src/disk.rs	Routes .vhdx open to the pure-Rust VHDX chain implementation.
openvmm/openvmm_helpers/Cargo.toml	Adds disklayer_vhdx dependency.
Cargo.toml	Adds workspace members + crc32c dependency.

[Copilot]

Pull request overview

Copilot reviewed 34 out of 41 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 34 out of 41 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 40 out of 47 changed files in this pull request and generated 9 comments.

[Copilot]

Pull request overview

Copilot reviewed 40 out of 47 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 40 out of 47 changed files in this pull request and generated 5 comments.

[Copilot]

Copilot wasn't able to review this pull request because it exceeds the maximum number of lines (20,000). Try reducing the number of changed lines and requesting a review from Copilot again.