workaround to get lower device name

src/kerneldevice/mm-kernel-device-helpers.c

@@ -24,6 +24,58 @@
 
 /******************************************************************************/
 
+static gboolean
+read_sysfs_int (const gchar *path,
+                gint        *value)
+{
+    g_autofree gchar *contents = NULL;
+    gchar            *end = NULL;
+    gint64            parsed;
+
+    if (!g_file_get_contents (path, &contents, NULL, NULL))
+        return FALSE;
+    parsed = g_ascii_strtoll (contents, &end, 10);
+    if (end == contents)
+        return FALSE;
+    *value = (gint) parsed;
+    return TRUE;
+}
+
+/* Net devices stacked by drivers that create no lower_* adjacency links (e.g. rmnet on Android vendor
+ * kernels) still report the parent's interface index in 'iflink'. */
+static gchar *
+get_lower_device_name_by_iflink (const gchar *sysfs_path)
+{
+    g_autofree gchar *ifindex_path = NULL;
+    g_autofree gchar *iflink_path = NULL;
+    g_autoptr(GDir)   dir = NULL;
+    const gchar      *name;
+    gint              ifindex;
+    gint              iflink;
+
+    ifindex_path = g_build_filename (sysfs_path, "ifindex", NULL);
+    iflink_path = g_build_filename (sysfs_path, "iflink", NULL);
+    if (!read_sysfs_int (ifindex_path, &ifindex) ||
+        !read_sysfs_int (iflink_path, &iflink) ||
+        iflink == ifindex || iflink <= 0)
+        return NULL;
+
+    dir = g_dir_open ("/sys/class/net", 0, NULL);
+    if (!dir)
+        return NULL;
+
+    while ((name = g_dir_read_name (dir)) != NULL) {
+        g_autofree gchar *path = NULL;
+        gint              index;
+
+        path = g_build_filename ("/sys/class/net", name, "ifindex", NULL);
+        if (read_sysfs_int (path, &index) && index == iflink)
+            return g_strdup (name);
+    }
+
+    return NULL;
+}
+
 gchar *
 mm_kernel_device_get_lower_device_name (const gchar *sysfs_path)
 {
@@ -60,7 +112,7 @@ mm_kernel_device_get_lower_device_name (const gchar *sysfs_path)
         return g_path_get_basename (real_path);
     }
 
-    return NULL;
+    return get_lower_device_name_by_iflink (sysfs_path);
 }
 
 /******************************************************************************/