Support priv/unpriv image extraction

Optionally add back privileged extraction which can be enabled with
LUET_PRIVILEGED_EXTRACT=true

Signed-off-by: Ettore Di Giacinto <mudler@sabayon.org>

pkg/helpers/imgworker/client.go

@@ -0,0 +1,81 @@
+package imgworker
+
+// FROM Slightly adapted from genuinetools/img worker
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+
+	"github.com/containerd/containerd/namespaces"
+	dockertypes "github.com/docker/docker/api/types"
+	"github.com/genuinetools/img/types"
+	"github.com/moby/buildkit/control"
+	"github.com/moby/buildkit/session"
+	"github.com/moby/buildkit/util/appcontext"
+	"github.com/moby/buildkit/worker/base"
+	"github.com/pkg/errors"
+)
+
+// Client holds the information for the client we will use for communicating
+// with the buildkit controller.
+type Client struct {
+	backend   string
+	localDirs map[string]string
+	root      string
+
+	sessionManager *session.Manager
+	controller     *control.Controller
+	opts           *base.WorkerOpt
+
+	sess *session.Session
+	ctx  context.Context
+	auth *dockertypes.AuthConfig
+}
+
+// New returns a new client for communicating with the buildkit controller.
+func New(root string, auth *dockertypes.AuthConfig) (*Client, error) {
+	// Native backend is fine, our images have just one layer. No need to depend on anything
+	backend := types.NativeBackend
+
+	// Create the root/
+	root = filepath.Join(root, "runc", backend)
+	if err := os.MkdirAll(root, 0700); err != nil {
+		return nil, err
+	}
+	c := &Client{
+		backend:   types.NativeBackend,
+		root:      root,
+		localDirs: nil,
+		auth:      auth,
+	}
+
+	if err := c.prepare(); err != nil {
+		return nil, errors.Wrapf(err, "failed preparing client")
+	}
+
+	// Create the start of the client.
+	return c, nil
+}
+
+func (c *Client) Close() {
+	c.sess.Close()
+}
+
+func (c *Client) prepare() error {
+	ctx := appcontext.Context()
+	sess, sessDialer, err := c.Session(ctx)
+	if err != nil {
+		return errors.Wrapf(err, "failed creating Session")
+	}
+	ctx = session.NewContext(ctx, sess.ID())
+	ctx = namespaces.WithNamespace(ctx, "buildkit")
+
+	c.ctx = ctx
+	c.sess = sess
+
+	go func() {
+		sess.Run(ctx, sessDialer)
+	}()
+	return nil
+}