jiangliu / vm-virtio

virtio implementation

vm-virtio

The vm-virtio crate provides a virtio device implementation:

• A virtio virtqueue and Descriptor chain API
• A virtio device trait (VirtioDevice)

Virtio Device trait

Virtio device implementations will implement the VirtioDevice trait. Typically the VMM will implement virtio devices and provide the paravirtualized IO emulation for all supported virtio devices. For example a VMM willing to emulate a virtio networking device will implement the VirtioDevice trait.

The VirtioDevice implementation will be discovered by the guest through a virtio transport layer (MMIO, PCI or channel IO). The transport layer implementation will then call into the VirtioDevice activate method to notify the device that the guest driver is done configuring it and that it should be ready to handle IO from the guest. On the other hand, the VirtioDevice reset method will be called by the transport layer when the guest driver needs to reset and release all the emulated device resources.

Virtio queue API

The vm-virtio queue API is to be consumed by virtio device implementations. The virtio device (net, block, rng, etc) implementation will call into the queue API to allocate and manage its specific virtio queues:

• new() to allocate its queues.

• iter() to iterate over the queue descriptors and consume virtio queue buffers made available by the guest driver.

• add_used() to place a virtio queue buffer into the queue and have the guest driver consume it.

Tests

Our Continuous Integration (CI) pipeline is implemented on top of Buildkite. For the complete list of tests, check our CI pipeline.

Each individual test runs in a container. To reproduce a test locally, you can use the dev-container on both x86 and arm64.

docker run -it \
           --security-opt seccomp=unconfined \
           --volume $(pwd):/vm-virtio \
           fandree/rust-vmm-dev
cd vm-virtio/
cargo test

Test Profiles

The integration tests support two test profiles:

• devel: this is the recommended profile for running the integration tests on a local development machine.

• ci (default option): this is the profile used when running the integration tests as part of the the Continuous Integration (CI).

The test profiles are applicable to tests that run using pytest. Currently only the coverage test follows this model as all the other integration tests are run using the Buildkite pipeline.

The difference between is declaring tests as passed or failed:

• with the devel profile the coverage test passes if the current coverage is equal or higher than the upstream coverage value. In case the current coverage is higher, the coverage file is updated to the new coverage value.

• with the ci profile the coverage test passes only if the current coverage is equal to the upstream coverage value.

Further details about the coverage test can be found in the Adaptive Coverage section.

Adaptive Coverage

The line coverage is saved in tests/coverage. To update the coverage before submitting a PR, run the coverage test:

docker run -it \
           --security-opt seccomp=unconfined \
           --volume $(pwd):/vm-virtio \
           fandree/rust-vmm-dev
cd vm-virtio/
pytest --profile=devel tests/test_coverage.py

If the PR coverage is higher than the upstream coverage, the coverage file needs to be manually added to the commit before submitting the PR:

git add tests/coverage

Failing to do so will generate a fail on the CI pipeline when publishing the PR.

NOTE: The coverage file is only updated in the devel test profile. In the ci profile the coverage test will fail if the current coverage is higher than the coverage reported in tests/coverage.