Introduce virtual machine backend interface

[Daman Mulye (damanm24)]

This PR introduces a new IVirtualMachineBackend that will be used by both WSL/WSLC to manage VMs that back their sessions. It also introduces a new OpenVmmVirtualMachineBackend class that provides a concrete implementation of the interface that can boot a minimal Linux VM. The long-term goal is to complete the OpenVmmVirtualMachineBackend implementation and provide a corresponding HcsVirtualMachineBackend implementation that both WSL and WSLC can use. Currently, the classes responsible for managing VMs for these two areas (WslCoreVm for WSL and WSLCVirtualMachine) have their product specific logic coupled with managing VMs. Eventually these classes will be refactored to split these two areas and provide better separation and single responsibility.

[Copilot]

Copilot review overview

🟡 Changes recommended

The backend’s advertised capabilities currently conflict with what the implementation actually supports (notably firmware boot and several unimplemented operations), which can mislead capability-driven callers.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2

Open (2)

• Advertised operations are unimplemented and fail with E_NOTIMPL · New
• Linux firmware boot capability is advertised but rejected · New

What changed in this PR

This PR introduces a new IVirtualMachineBackend abstraction in the Windows service layer, plus an initial OpenVmmVirtualMachineBackend implementation intended to become a shared VM-management layer for both WSL and WSLC.

Changes:

• Added IVirtualMachineBackend API surface and factory helpers for selecting/querying a backend.
• Implemented an initial OpenVMM-backed VM backend with request validation, process lifecycle, and basic disk attach/detach.
• Added Windows tests and build/package wiring to bring in OpenVMM binaries and required boot artifacts.

File	Description
test/​windows/​OpenVmmVirtualMachineBackendTests.cpp	Adds validation, lifecycle, and capability tests for the OpenVMM backend.
test/​windows/​CMakeLists.txt	Wires the new test into wsltests and stages the kernel dependency.
src/​windows/​service/​exe/​VirtualMachineBackend.cpp	Adds factory functions to create/query a backend by BackendKind.
src/​windows/​service/​exe/​OpenVmmVirtualMachineBackend.h	Declares the OpenVMM backend implementation of IVirtualMachineBackend.
src/​windows/​service/​exe/​OpenVmmVirtualMachineBackend.cpp	Implements OpenVMM VM creation/teardown, request validation, and disk attach/detach plumbing.
src/​windows/​service/​exe/​IVirtualMachineBackend.h	Introduces the cross-backend interface and shared request/description types.
src/​windows/​service/​exe/​CMakeLists.txt	Adds the virtualmachinebackend static lib and links it into wslservice.
packages.config	Adds the Microsoft.WSL.OpenVMM NuGet dependency.
msipackage/​package.wix.in	Adds openvmm.exe and wslopenvmm.dll to the MSI payload.
msipackage/​CMakeLists.txt	Includes OpenVMM binaries in the packaging input list.
CMakeLists.txt	Locates the OpenVMM package and wires an imported client library plus binary staging into bin/.
.pipelines/​wsl-build-pr.yml	Expands PR build trigger patterns to include feature/* branches.

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[Copilot]

Copilot review overview

🟡 Changes recommended

It introduces contract/build reliability issues (capabilities advertising unimplemented operations and tests/build steps depending on unguarded external kernel artifacts) that can cause runtime failures or broken builds.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 3 · 1

Open (4)

• Align VmOperation with IVirtualMachineBackend methods · New
• Guard kernel copy when KERNEL_SOURCE_DIR is unset · New
• Skip boot test when kernel artifacts are missing · New
• Update capability test expectations for implemented operations · New

Resolved since last review (2)

• Linux firmware boot capability is advertised but rejected
• Advertised operations are unimplemented and fail with E_NOTIMPL

[Copilot]

Copilot review overview

🟡 Changes recommended

It introduces build/runtime inconsistencies (OpenVMM binaries no longer placed in the base path expected by the new backend/tests) and advertises a capability (UpdateNetworkAdapter) that has no corresponding interface method.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1 · 3 · 1

Open (5)

• OpenVMM binaries are missing from the build output directory · New
• Skip boot test when kernel artifacts are missing
• Guard kernel copy when KERNEL_SOURCE_DIR is unset
• Align VmOperation with IVirtualMachineBackend methods
• Update capability test expectations for implemented operations

[Copilot]

Copilot review overview

🟡 Changes recommended

Socket cleanup can leak VM directories, and the new test file fails the repository copyright validation.

Get a fresh assessment by requesting another Copilot review.

Review effort: Balanced
Findings: 2 · 1

Open (3)

• Remove generated service socket before deleting the hvsock directory · New
• Align VmOperation with IVirtualMachineBackend methods
• Add required copyright header to the new test source · New

Resolved since last review (4)

• OpenVMM binaries are missing from the build output directory
• Skip boot test when kernel artifacts are missing
• Guard kernel copy when KERNEL_SOURCE_DIR is unset
• Update capability test expectations for implemented operations

[Copilot]

Copilot review overview

🔵 Needs a closer look

ARM64 capabilities contradict creation support, and runtime disk operations lack coverage.

Review effort: Balanced
Findings: None

Resolved since last review (3)

• Remove generated service socket before deleting the hvsock directory
• Align VmOperation with IVirtualMachineBackend methods
• Add required copyright header to the new test source

Previously missed (2)

In code that hasn't changed since last review

Fix ARM64 capability expectation for unsupported create requests

test/​windows/​OpenVmmVirtualMachineBackendTests.cpp:215

This expectation is incorrect on ARM64: ValidateCreateRequest() unconditionally rejects every create request there, but this unskipped test requires LinuxDirectBoot to be advertised. A capability-driven caller can therefore select OpenVMM on ARM64 even though creation is guaranteed to fail. Make the queried capabilities platform-aware and update this expectation accordingly.

Add integration coverage for runtime disk attach and detach

src/​windows/​service/​exe/​OpenVmmVirtualMachineBackend.cpp:549

The new runtime disk path is untested. Existing disk tests only exercise ValidateCreateRequest() for boot disks, so regressions in the C ABI attach call, ID/LUN allocation, rollback, and DetachDisk() bookkeeping would not be detected. Add an integration test that boots a VM, attaches a test VHD, validates the returned attachment, and detaches it (including an explicit-placement or duplicate-LUN case).