vmtest

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vmtest

vmtest is a Go API for launching QEMU VMs.

• The qemu package contains APIs for

  • launching QEMU processes

  • configuring QEMU devices (such as a shared 9P directory, networking, serial logging, etc)

  • running tasks (goroutines) bound to the VM process lifetime, and

  • using expect-scripting to check for outputs.

  • quimage can be used to configure a Go-based u-root initramfs to be used as the root file system, including any arbitrary Go commands.

  • qnetwork (WIP) is an API to QEMU network devices.

  • qevent provides a JSON-over-virtio-serial channel from guest to host.

  • qcoverage adds utilities to collect kernel & Go GOCOVERDIR-based integration test coverage.

• The govmtest package (WIP) contains an API for running Go unit tests in the guest and collecting their test coverage as well as results.

• The scriptvm package (WIP) contains an API for running shell scripts in the guest.

Running Tests

The qemu API picks up the following values from env vars by default:

• VMTEST_QEMU: QEMU binary + arguments (e.g. VMTEST_QEMU="qemu-system-x86_64 -enable-kvm")
• VMTEST_KERNEL: Kernel to boot.
• VMTEST_ARCH: Guest architecture (same as GOARCH values). Must match the QEMU binary supplied. If not supplied, defaults to runtime.GOARCH, i.e. it matches the host's GOARCH.
• VMTEST_KERNEL_APPEND: is added to kernel command-line arguments
• VMTEST_QEMU_APPEND: is added to QEMU command-line arguments.
• VMTEST_TIMEOUT: Timeout value (e.g. 1m20s -- parsed by Go's time.ParseDuration).
• VMTEST_INITRAMFS: Initramfs to boot.

Most of these values can be overriden in the Go API, but typically only VMTEST_INITRAMFS and VMTEST_TIMEOUT are. VMTEST_KERNEL_APPEND and VMTEST_QEMU_APPEND are always additive.

The runvmtest tool automatically downloads VMTEST_QEMU and VMTEST_KERNEL for use with tests based on a provided VMTEST_ARCH. E.g.

go install github.com/hugelgupf/vmtest/tools/runvmtest@latest

# See how it works:
runvmtest -- bash -c "echo \$VMTEST_KERNEL -- \$VMTEST_QEMU"

# Intended usage:
runvmtest -- go test -v ./tests/gohello

# Or run an Arm64 guest:
VMTEST_ARCH=arm64 runvmtest -- go test -v ./tests/gohello

You can also override one or both, which will just be passed through:

# Will only download VMTEST_KERNEL.
VMTEST_ARCH=arm64 VMTEST_QEMU="qemu-system-aarch64 -enable-kvm" runvmtest -- go test -v ./tests/gohello

To keep the artifacts around locally to reproduce the same test:

runvmtest --keep-artifacts -- go test -v ./tests/gohello

The default kernel and QEMU supplied by runvmtest may of course not work well for your tests. You can configure runvmtest to supply your own VMTEST_KERNEL and VMTEST_QEMU -- but also any additional environment variables. See runvmtest configuration.

To build your own kernel or QEMU, check out images/kernel-arm64 for building a kernel-image-only Docker image, and images/qemu for how we build a Docker image with just QEMU binaries and their dependencies.

Writing Tests

Architecture-independent test with shared directory

The recommendation for architecture-independent tests is to allow architecture-dependent values like VMTEST_QEMU and VMTEST_KERNEL be provided by runvmtest based on VMTEST_ARCH, while configuring everything else with the Go API.

See e.g. examples/shareddir

Run it with:

$ cd examples/shareddir
$ VMTEST_ARCH=amd64 runvmtest -- go test -v
$ VMTEST_ARCH=arm64 runvmtest -- go test -v
$ VMTEST_ARCH=riscv64 runvmtest -- go test -v
$ VMTEST_ARCH=arm runvmtest -- go test -v

They all should pass.

Every test in this repository is written this way to test every feature on all architectures.

Example: Go unit tests in VM

See tests/gobench

Example: qemu API with u-root initramfs

func TestStartVM(t *testing.T) {
    vm := qemu.StartT(
        t,
        "vm", // Prefix for t.Logf serial console lines.
        qemu.ArchUseEnvv,
        quimage.WithUimageT(t,
                uimage.WithInit("init"),
                uimage.WithUinit("shutdownafter", "--", "cat", "etc/thatfile"),
                uimage.WithBusyboxCommands(
                        "github.com/u-root/u-root/cmds/core/init",
                        "github.com/u-root/u-root/cmds/core/cat",
                        "github.com/hugelgupf/vmtest/vminit/shutdownafter",
                ),
                uimage.WithFiles("./testdata/foo:etc/thatfile"),
        ),

        // Other options...
    )
    // ...
}

Example: qemu API

The qemu API can be used without testing.TB, and any of the environment variables can be overridden in the Go API:

func TestStartVM(t *testing.T) {
    vm, err := qemu.Start(
        // Or use qemu.ArchUseEnvv and set VMTEST_ARCH=amd64 (values like GOARCH)
        qemu.ArchAMD64,

        // Or omit and set VMTEST_QEMU="qemu-system-x86_64 -enable-kvm"
        qemu.WithQEMUCommand("qemu-system-x86_64 -enable-kvm"),

        // Or omit and set VMTEST_KERNEL=./foobar
        qemu.WithKernel("./foobar"),

        // Or omit and set VMTEST_INITRAMFS=./somewhere.cpio
        // Or use u-root initramfs builder in quimage package. See example below.
        qemu.WithInitramfs("./somewhere.cpio"),

        qemu.WithAppendKernel("console=ttyS0 earlyprintk=ttyS0"),
        qemu.LogSerialByLine(qemu.DefaultPrint("vm", t.Logf)),
    )
    if err != nil {
        t.Fatalf("Failed to start VM: %v", err)
    }
    t.Logf("cmdline: %#v", vm.CmdlineQuoted())

    if _, err := vm.Console.ExpectString("Kernel command line:"); err != nil {
        t.Errorf("Error expecting kernel command line string: %v", err)
    }

    if err := vm.Wait(); err != nil {
        t.Fatalf("Error waiting for VM to exit: %v", err)
    }
}

Example: Tasks

func TestStartVM(t *testing.T) {
    vm, err := qemu.Start(
        qemu.ArchUseEnvv,
        // Other config ...

        // Runs a goroutine alongside the QEMU process, which is canceled via
        // context when QEMU exits.
        qemu.WithTask(
            func(ctx context.Context, n *qemu.Notifications) error {
                // If this were an HTTP server or something not expected to exit
                // cleanly when the guest exits, probably want to ignore SIGKILL error.
                return exec.CommandContext(ctx, "sleep", "900").Run()
            },
        ),

        // Task that runs when the VM exits.
        qemu.WithTask(qemu.Cleanup(func() error {
            // Do something.
            return fmt.Errorf("this is returned by vm.Wait()")
        })),

        // Task that only runs when VM starts.
        qemu.WithTask(qemu.WaitVMStarted(...)),
    )
    // ...
}

Custom runvmtest configuration

runvmtest tries to read a config from .vmtest.yaml in the current working directory or any of its parents.

Given this is a Go-based test framework, the recommendation would be to place .vmtest.yaml in the same directory as your go.mod so that the config is available anywhere go test is for that module.

runvmtest can be configured to set up any number of environment variables. Config format looks like this:

VMTEST_ARCH:
  ENV_VAR:
    container: <container name>
    template: "{{.somedir}} -foobar {{.somefile}}"
    files:
      somefile: <path in container to copy to a tmpfile>
    directories:
      somedir: <path in container to copy to a tmpdir>

Check out the example in tools/runvmtest/example-vmtest.yaml.