Add jgvariant-ostree module.

Change-Id: Idf7bacad28d7cf65eb1ddd0994dcc2c2c2a7e18e
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Xattr.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Xattr.java
new file mode 100644
index 0000000..68628c4
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Xattr.java
@@ -0,0 +1,18 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+
+/**
+ * Reference: (embedded in other data types, e.g. {@code
+ * ostree-core.h#OSTREE_DIRMETA_GVARIANT_STRING}, {@code
+ * ostree-core.h#OSTREE_FILEMETA_GVARIANT_STRING})
+ */
+public record Xattr(ByteString name, ByteString value) {
+
+  private static final Decoder<Xattr> DECODER =
+      Decoder.ofStructure(Xattr.class, ByteString.decoder(), ByteString.decoder());
+
+  public static Decoder<Xattr> decoder() {
+    return DECODER;
+  }
+}