Add kubevirt platform ID

The KubeVirt platform provides config drive files compatible to the
openstack config drive like nutanix does. It provides a disk with a
`config-2` label (lower case).

Signed-off-by: Roman Mohr <rmohr@redhat.com>

internal/platform/platform.go

@@ -29,6 +29,7 @@ import (
 	"github.com/coreos/ignition/v2/internal/providers/file"
 	"github.com/coreos/ignition/v2/internal/providers/gcp"
 	"github.com/coreos/ignition/v2/internal/providers/ibmcloud"
+	"github.com/coreos/ignition/v2/internal/providers/kubevirt"
 	"github.com/coreos/ignition/v2/internal/providers/noop"
 	"github.com/coreos/ignition/v2/internal/providers/nutanix"
 	"github.com/coreos/ignition/v2/internal/providers/openstack"
@@ -141,6 +142,10 @@ func init() {
 		name:  "ibmcloud",
 		fetch: ibmcloud.FetchConfig,
 	})
+	configs.Register(Config{
+		name:  "kubevirt",
+		fetch: kubevirt.FetchConfig,
+	})
 	configs.Register(Config{
 		name:  "metal",
 		fetch: noop.FetchConfig,

internal/providers/kubevirt/kubevirt.go

@@ -0,0 +1,91 @@
+// Copyright 2021 Red Hat.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// The KubeVirt (https://kubevirt.io) provider fetches
+// configuration from the userdata available in the config-drive. It is similar
+// to Openstack and uses the same APIs.
+
+package kubevirt
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"time"
+
+	"github.com/coreos/ignition/v2/config/v3_4_experimental/types"
+	"github.com/coreos/ignition/v2/internal/distro"
+	"github.com/coreos/ignition/v2/internal/log"
+	"github.com/coreos/ignition/v2/internal/providers/util"
+	"github.com/coreos/ignition/v2/internal/resource"
+	ut "github.com/coreos/ignition/v2/internal/util"
+
+	"github.com/coreos/vcontext/report"
+)
+
+const (
+	configDriveUserdataPath = "/openstack/latest/user_data"
+)
+
+func FetchConfig(f *resource.Fetcher) (types.Config, report.Report, error) {
+	data, err := fetchConfigFromDevice(f.Logger, filepath.Join(distro.DiskByLabelDir(), "config-2"))
+	if err != nil {
+		return types.Config{}, report.Report{}, err
+	}
+
+	return util.ParseConfig(f.Logger, data)
+}
+
+func fileExists(path string) bool {
+	_, err := os.Stat(path)
+	return (err == nil)
+}
+
+func fetchConfigFromDevice(logger *log.Logger, path string) ([]byte, error) {
+	// There is not always a config drive in kubevirt, but we can limit rhcos usage
+	// to VMs with config drives. Block forever if there is none.
+	for !fileExists(path) {
+		logger.Debug("config drive (%q) not found. Waiting...", path)
+		time.Sleep(time.Second)
+	}
+
+	logger.Debug("creating temporary mount point")
+	mnt, err := ioutil.TempDir("", "ignition-configdrive")
+	if err != nil {
+		return nil, fmt.Errorf("failed to create temp directory: %v", err)
+	}
+	defer os.Remove(mnt)
+
+	cmd := exec.Command(distro.MountCmd(), "-o", "ro", "-t", "auto", path, mnt)
+	if _, err := logger.LogCmd(cmd, "mounting config drive"); err != nil {
+		return nil, err
+	}
+	defer func() {
+		_ = logger.LogOp(
+			func() error {
+				return ut.UmountPath(mnt)
+			},
+			"unmounting %q at %q", path, mnt,
+		)
+	}()
+
+	mntConfigDriveUserdataPath := filepath.Join(mnt, configDriveUserdataPath)
+	if !fileExists(mntConfigDriveUserdataPath) {
+		return nil, nil
+	}
+
+	return ioutil.ReadFile(mntConfigDriveUserdataPath)
+}