vendor: add buildkit

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/tonistiigi/fsutil/hardlinks.go

@@ -0,0 +1,47 @@
+package fsutil
+
+import (
+	"os"
+
+	"github.com/pkg/errors"
+	"github.com/tonistiigi/fsutil/types"
+)
+
+// Hardlinks validates that all targets for links were part of the changes
+
+type Hardlinks struct {
+	seenFiles map[string]struct{}
+}
+
+func (v *Hardlinks) HandleChange(kind ChangeKind, p string, fi os.FileInfo, err error) error {
+	if err != nil {
+		return err
+	}
+
+	if v.seenFiles == nil {
+		v.seenFiles = make(map[string]struct{})
+	}
+
+	if kind == ChangeKindDelete {
+		return nil
+	}
+
+	stat, ok := fi.Sys().(*types.Stat)
+	if !ok {
+		return errors.Errorf("invalid change without stat info: %s", p)
+	}
+
+	if fi.IsDir() || fi.Mode()&os.ModeSymlink != 0 {
+		return nil
+	}
+
+	if len(stat.Linkname) > 0 {
+		if _, ok := v.seenFiles[stat.Linkname]; !ok {
+			return errors.Errorf("invalid link %s to unknown path: %q", p, stat.Linkname)
+		}
+	} else {
+		v.seenFiles[p] = struct{}{}
+	}
+
+	return nil
+}