Update Unstage transaction to undo steps done in Stage

In unstage we now adhere to the transaction (or order of steps)
done in Stage. To enable this we stash the image meta data
into a local file on the staging path for use with unstage
request.

This helps in unmapping a stale map, in case the mount or
other steps in the transaction are complete.

Signed-off-by: ShyamsundarR <srangana@redhat.com>

pkg/rbd/rbd_util.go

@@ -19,7 +19,10 @@ package rbd
 import (
 	"encoding/json"
 	"fmt"
+	"io/ioutil"
+	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 	"time"
 
@@ -704,3 +707,76 @@ func getSnapInfo(monitors string, cr *util.Credentials, poolName, imageName, sna
 	return snpInfo, ErrSnapNotFound{snapName, fmt.Errorf("snap (%s) for image (%s) not found",
 		snapName, poolName+"/"+imageName)}
 }
+
+// rbdImageMetadataStash strongly typed JSON spec for stashed RBD image metadata
+type rbdImageMetadataStash struct {
+	Version   int    `json:"Version"`
+	Pool      string `json:"pool"`
+	ImageName string `json:"image"`
+	NbdAccess bool   `json:"accessType"`
+}
+
+// file name in which image metadata is stashed
+const stashFileName = "image-meta.json"
+
+// stashRBDImageMetadata stashes required fields into the stashFileName at the passed in path, in
+// JSON format
+func stashRBDImageMetadata(volOptions *rbdVolume, path string) error {
+	var imgMeta = rbdImageMetadataStash{
+		Version:   1, // Stash a v1 for now, in case of changes later, there are no checks for this at present
+		Pool:      volOptions.Pool,
+		ImageName: volOptions.RbdImageName,
+	}
+
+	imgMeta.NbdAccess = false
+	if volOptions.Mounter == rbdTonbd && hasNBD {
+		imgMeta.NbdAccess = true
+	}
+
+	encodedBytes, err := json.Marshal(imgMeta)
+	if err != nil {
+		return fmt.Errorf("failed to marshall JSON image metadata for image (%s) in pool (%s): (%v)",
+			volOptions.RbdImageName, volOptions.Pool, err)
+	}
+
+	fPath := filepath.Join(path, stashFileName)
+	err = ioutil.WriteFile(fPath, encodedBytes, 0600)
+	if err != nil {
+		return fmt.Errorf("failed to stash JSON image metadata for image (%s) in pool (%s) at path (%s): (%v)",
+			volOptions.RbdImageName, volOptions.Pool, fPath, err)
+	}
+
+	return nil
+}
+
+// lookupRBDImageMetadataStash reads and returns stashed image metadata at passed in path
+func lookupRBDImageMetadataStash(path string) (rbdImageMetadataStash, error) {
+	var imgMeta rbdImageMetadataStash
+
+	fPath := filepath.Join(path, stashFileName)
+	encodedBytes, err := ioutil.ReadFile(fPath)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return imgMeta, fmt.Errorf("failed to read stashed JSON image metadata from path (%s): (%v)", fPath, err)
+		}
+
+		return imgMeta, ErrMissingStash{err}
+	}
+
+	err = json.Unmarshal(encodedBytes, &imgMeta)
+	if err != nil {
+		return imgMeta, fmt.Errorf("failed to unmarshall stashed JSON image metadata from path (%s): (%v)", fPath, err)
+	}
+
+	return imgMeta, nil
+}
+
+// cleanupRBDImageMetadataStash cleans up any stashed metadata at passed in path
+func cleanupRBDImageMetadataStash(path string) error {
+	fPath := filepath.Join(path, stashFileName)
+	if err := os.Remove(fPath); err != nil {
+		return fmt.Errorf("failed to cleanup stashed JSON data (%s): (%v)", fPath, err)
+	}
+
+	return nil
+}