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>

vendor/github.com/moby/buildkit/solver/cachestorage.go

@@ -0,0 +1,51 @@
+package solver
+
+import (
+	"context"
+	"time"
+
+	digest "github.com/opencontainers/go-digest"
+	"github.com/pkg/errors"
+)
+
+var ErrNotFound = errors.Errorf("not found")
+
+// CacheKeyStorage is interface for persisting cache metadata
+type CacheKeyStorage interface {
+	Exists(id string) bool
+	Walk(fn func(id string) error) error
+
+	WalkResults(id string, fn func(CacheResult) error) error
+	Load(id string, resultID string) (CacheResult, error)
+	AddResult(id string, res CacheResult) error
+	Release(resultID string) error
+	WalkIDsByResult(resultID string, fn func(string) error) error
+
+	AddLink(id string, link CacheInfoLink, target string) error
+	WalkLinks(id string, link CacheInfoLink, fn func(id string) error) error
+	HasLink(id string, link CacheInfoLink, target string) bool
+	WalkBacklinks(id string, fn func(id string, link CacheInfoLink) error) error
+}
+
+// CacheResult is a record for a single solve result
+type CacheResult struct {
+	CreatedAt time.Time
+	ID        string
+}
+
+// CacheInfoLink is a link between two cache keys
+type CacheInfoLink struct {
+	Input    Index         `json:"Input,omitempty"`
+	Output   Index         `json:"Output,omitempty"`
+	Digest   digest.Digest `json:"Digest,omitempty"`
+	Selector digest.Digest `json:"Selector,omitempty"`
+}
+
+// CacheResultStorage is interface for converting cache metadata result to
+// actual solve result
+type CacheResultStorage interface {
+	Save(Result, time.Time) (CacheResult, error)
+	Load(ctx context.Context, res CacheResult) (Result, error)
+	LoadRemote(ctx context.Context, res CacheResult) (*Remote, error)
+	Exists(id string) bool
+}