[#791] writecache: Export OpenDB function

The function will be useful for the tool which works with write-cache parts.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/writecache/util.go

@@ -0,0 +1,17 @@
+package writecache
+
+import (
+	"os"
+	"path"
+
+	"go.etcd.io/bbolt"
+)
+
+// OpenDB opens BoltDB instance for write-cache. Opens in read-only mode if ro is true.
+func OpenDB(p string, ro bool) (*bbolt.DB, error) {
+	return bbolt.Open(path.Join(p, dbName), os.ModePerm, &bbolt.Options{
+		NoFreelistSync: true,
+		NoSync:         true,
+		ReadOnly:       ro,
+	})
+}