openstack: dynamically mount the config-drive

When we want to use config-drive in immutable systems, very often the
config-drive is only used at boot and then umounted (e.g. ignition does
this).

Later when we want to fetch Metadata from the config drive, we actually
have to mount it.

In this PR, I'm adding similar code than coreos/ignition where we
dynamically mount the config-drive is the device was found with the
right label (config-2 or CONFIG-2 as documented in OpenStack). If the
device is found, we mount it, fetch the data and umount it.

pkg/platforms/openstack/openstack.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"os/exec"
+	"path/filepath"
 	"strconv"
 	"strings"
 
@@ -21,15 +23,14 @@ import (
 )
 
 const (
-	ospHostMetaDataDir     = "/host/var/config/openstack/2018-08-27"
-	ospMetaDataDir         = "/var/config/openstack/2018-08-27"
-	ospMetaDataBaseURL     = "http://169.254.169.254/openstack/2018-08-27"
-	ospNetworkDataJSON     = "network_data.json"
-	ospMetaDataJSON        = "meta_data.json"
-	ospHostNetworkDataFile = ospHostMetaDataDir + "/" + ospNetworkDataJSON
-	ospHostMetaDataFile    = ospHostMetaDataDir + "/" + ospMetaDataJSON
-	ospNetworkDataURL      = ospMetaDataBaseURL + "/" + ospNetworkDataJSON
-	ospMetaDataURL         = ospMetaDataBaseURL + "/" + ospMetaDataJSON
+	varConfigPath      = "/var/config"
+	ospMetaDataBaseDir = "/openstack/2018-08-27"
+	ospMetaDataDir     = varConfigPath + ospMetaDataBaseDir
+	ospMetaDataBaseURL = "http://169.254.169.254" + ospMetaDataBaseDir
+	ospNetworkDataJSON = "network_data.json"
+	ospMetaDataJSON    = "meta_data.json"
+	ospNetworkDataURL  = ospMetaDataBaseURL + "/" + ospNetworkDataJSON
+	ospMetaDataURL     = ospMetaDataBaseURL + "/" + ospMetaDataJSON
 )
 
 var (
@@ -109,8 +110,8 @@ func New(hostManager host.HostManagerInterface) OpenstackInterface {
 }
 
 // GetOpenstackData gets the metadata and network_data
-func getOpenstackData(useHostPath bool) (metaData *OSPMetaData, networkData *OSPNetworkData, err error) {
-	metaData, networkData, err = getOpenstackDataFromConfigDrive(useHostPath)
+func getOpenstackData(mountConfigDrive bool) (metaData *OSPMetaData, networkData *OSPNetworkData, err error) {
+	metaData, networkData, err = getOpenstackDataFromConfigDrive(mountConfigDrive)
 	if err != nil {
 		metaData, networkData, err = getOpenstackDataFromMetadataService()
 		if err != nil {
@@ -153,46 +154,102 @@ func getOpenstackData(useHostPath bool) (metaData *OSPMetaData, networkData *OSP
 	return metaData, networkData, err
 }
 
+// fileExists checks if a file exists and returns a boolean
+func fileExists(path string) bool {
+	_, err := os.Stat(path)
+	return (err == nil)
+}
+
+// getConfigDriveLabel returns the config drive label that was found
+// either "config-2" or "CONFIG-2" or empty string if not found
+func getConfigDriveLabel() string {
+	var configDriveLabel string
+	if fileExists("/dev/disk/by-label/config-2") {
+		configDriveLabel = "config-2"
+	} else if fileExists("/dev/disk/by-label/CONFIG-2") {
+		configDriveLabel = "CONFIG-2"
+	}
+	return configDriveLabel
+}
+
+// mountConfigDriveByLabel mounts the config drive by label and return its path
+func mountConfigDriveByLabel(configDriveLabel string) (string, error) {
+	tmpDir, err := os.MkdirTemp("", "sriov-configdrive")
+	if err != nil {
+		return "", fmt.Errorf("error creating temp directory: %w", err)
+	}
+	configDrivePath := "/dev/disk/by-label/" + configDriveLabel
+	cmd := exec.Command("mount", "-o", "ro", "-t", "auto", configDrivePath, tmpDir)
+	if err := cmd.Run(); err != nil {
+		return "", fmt.Errorf("error mounting config drive: %w", err)
+	}
+	return tmpDir, nil
+}
+
+// ummountConfigDriveByLabel ummounts the config drive by label
+func ummountConfigDriveByLabel(configDrivePath string) error {
+	cmd := exec.Command("umount", configDrivePath)
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("error umounting config drive: %w", err)
+	}
+	return nil
+}
+
 // getOpenstackDataFromConfigDrive reads the meta_data and network_data files
-func getOpenstackDataFromConfigDrive(useHostPath bool) (metaData *OSPMetaData, networkData *OSPNetworkData, err error) {
+func getOpenstackDataFromConfigDrive(mountConfigDrive bool) (metaData *OSPMetaData, networkData *OSPNetworkData, err error) {
 	metaData = &OSPMetaData{}
 	networkData = &OSPNetworkData{}
+	var configDrivePath string
 	log.Log.Info("reading OpenStack meta_data from config-drive")
 	var metadataf *os.File
 	ospMetaDataFilePath := ospMetaDataFile
-	if useHostPath {
-		ospMetaDataFilePath = ospHostMetaDataFile
+	if mountConfigDrive {
+		configDriveLabel := getConfigDriveLabel()
+		if ospMetaDataFilePath == "" {
+			return metaData, networkData, fmt.Errorf("error finding config drive device")
+		}
+		configDrivePath, err = mountConfigDriveByLabel(configDriveLabel)
+		if err != nil {
+			return metaData, networkData, fmt.Errorf("error mounting config drive with label %s: %w", configDriveLabel, err)
+		}
+		defer func() {
+			if e := ummountConfigDriveByLabel(configDrivePath); err == nil && e != nil {
+				err = fmt.Errorf("error umounting config drive with label %s: %w", configDriveLabel, e)
+			}
+			if e := os.Remove(configDrivePath); err == nil && e != nil {
+				err = fmt.Errorf("error removing temp directory %s: %w", configDrivePath, e)
+			}
+		}()
+		ospMetaDataFilePath = filepath.Join(configDrivePath, ospMetaDataBaseDir, ospMetaDataJSON)
+		ospNetworkDataFile = filepath.Join(configDrivePath, ospMetaDataBaseDir, ospNetworkDataJSON)
 	}
 	metadataf, err = os.Open(ospMetaDataFilePath)
 	if err != nil {
-		return metaData, networkData, fmt.Errorf("error opening file %s: %w", ospHostMetaDataFile, err)
+		return metaData, networkData, fmt.Errorf("error opening file %s: %w", ospMetaDataFilePath, err)
 	}
 	defer func() {
 		if e := metadataf.Close(); err == nil && e != nil {
-			err = fmt.Errorf("error closing file %s: %w", ospHostMetaDataFile, e)
+			err = fmt.Errorf("error closing file %s: %w", ospMetaDataFilePath, e)
 		}
 	}()
 	if err = json.NewDecoder(metadataf).Decode(&metaData); err != nil {
-		return metaData, networkData, fmt.Errorf("error unmarshalling metadata from file %s: %w", ospHostMetaDataFile, err)
+		return metaData, networkData, fmt.Errorf("error unmarshalling metadata from file %s: %w", ospMetaDataFilePath, err)
 	}
 
 	log.Log.Info("reading OpenStack network_data from config-drive")
 	var networkDataf *os.File
 	ospNetworkDataFilePath := ospNetworkDataFile
-	if useHostPath {
-		ospNetworkDataFilePath = ospHostNetworkDataFile
-	}
 	networkDataf, err = os.Open(ospNetworkDataFilePath)
 	if err != nil {
-		return metaData, networkData, fmt.Errorf("error opening file %s: %w", ospHostNetworkDataFile, err)
+		return metaData, networkData, fmt.Errorf("error opening file %s: %w", ospNetworkDataFilePath, err)
 	}
 	defer func() {
 		if e := networkDataf.Close(); err == nil && e != nil {
-			err = fmt.Errorf("error closing file %s: %w", ospHostNetworkDataFile, e)
+			err = fmt.Errorf("error closing file %s: %w", ospNetworkDataFilePath, e)
 		}
 	}()
 	if err = json.NewDecoder(networkDataf).Decode(&networkData); err != nil {
-		return metaData, networkData, fmt.Errorf("error unmarshalling metadata from file %s: %w", ospHostNetworkDataFile, err)
+		return metaData, networkData, fmt.Errorf("error unmarshalling metadata from file %s: %w", ospNetworkDataFilePath, err)
 	}
 	return metaData, networkData, err
 }