diff --git a/include/hwloc.h b/include/hwloc.h
index a1cb836..b6b1f7e 100644
--- a/include/hwloc.h
+++ b/include/hwloc.h
@@ -371,7 +371,10 @@ struct hwloc_obj {
   struct hwloc_obj *last_child;		/**< \brief Last child */
 
   /* misc */
-  void *userdata;			/**< \brief Application-given private data pointer, initialized to \c NULL, use it as you wish */
+  void *userdata;			/**< \brief Application-given private data pointer,
+					 * initialized to \c NULL, use it as you wish.
+					 * See hwloc_topology_set_userdata_export_callback()
+					 * if you wish to export this field to XML. */
 
   /* cpusets and nodesets */
   hwloc_cpuset_t cpuset;		/**< \brief CPUs covered by this object
@@ -825,6 +828,9 @@ HWLOC_DECLSPEC int hwloc_topology_set_synthetic(hwloc_topology_t __hwloc_restric
  *
  * \return -1 with errno set to EINVAL on failure to read the XML file.
  *
+ * \note See also hwloc_topology_set_userdata_import_callback()
+ * for importing application-specific userdata.
+ *
  * \note For convenience, this backend provides empty binding hooks which just
  * return success.  To have hwloc still actually call OS-specific hooks, the
  * HWLOC_TOPOLOGY_FLAG_IS_THISSYSTEM has to be set to assert that the loaded
@@ -848,6 +854,9 @@ HWLOC_DECLSPEC int hwloc_topology_set_xml(hwloc_topology_t __hwloc_restrict topo
  *
  * \return -1 with errno set to EINVAL on failure to read the XML buffer.
  *
+ * \note See also hwloc_topology_set_userdata_import_callback()
+ * for importing application-specific userdata.
+ *
  * \note For convenience, this backend provides empty binding hooks which just
  * return success.  To have hwloc still actually call OS-specific hooks, the
  * HWLOC_TOPOLOGY_FLAG_IS_THISSYSTEM has to be set to assert that the loaded
@@ -985,6 +994,9 @@ HWLOC_DECLSPEC const struct hwloc_topology_support *hwloc_topology_get_support(h
  *
  * \return -1 if a failure occured.
  *
+ * \note See also hwloc_topology_set_userdata_export_callback()
+ * for exporting application-specific userdata.
+ *
  * \note Only printable characters may be exported to XML string attributes.
  * Any other character, especially any non-ASCII character, will be silently
  * dropped.
@@ -1000,6 +1012,9 @@ HWLOC_DECLSPEC int hwloc_topology_export_xml(hwloc_topology_t topology, const ch
  *
  * \return -1 if a failure occured.
  *
+ * \note See also hwloc_topology_set_userdata_export_callback()
+ * for exporting application-specific userdata.
+ *
  * \note Only printable characters may be exported to XML string attributes.
  * Any other character, especially any non-ASCII character, will be silently
  * dropped.
@@ -1009,6 +1024,59 @@ HWLOC_DECLSPEC int hwloc_topology_export_xmlbuffer(hwloc_topology_t topology, ch
 /** \brief Free a buffer allocated by hwloc_topology_export_xmlbuffer() */
 HWLOC_DECLSPEC void hwloc_free_xmlbuffer(hwloc_topology_t topology, char *xmlbuffer);
 
+/** \brief Set the application-specific callback for exporting userdata
+ *
+ * The object userdata pointer is not exported to XML by default because hwloc
+ * does not know what it contains.
+ *
+ * This function lets applications set \p export to a callback function
+ * that converts this opaque userdata into an exportable string.
+ * The callback will be invoked during XML export for each object
+ * whose \p userdata pointer is not \c NULL.
+ * The callback should use hwloc_export_obj_userdata() to actually export
+ * something to XML (possibly multiple times per object).
+ *
+ * \p export may be set to \c NULL if userdata should not be exported to XML.
+ */
+HWLOC_DECLSPEC void hwloc_topology_set_userdata_export_callback(hwloc_topology_t topology,
+								void (*export)(void *reserved, hwloc_topology_t topology, hwloc_obj_t obj));
+
+/** \brief Export some object userdata to XML
+ *
+ * This function may only be called from within the export() callback passed
+ * to hwloc_topology_set_userdata_export_callback().
+ * It may be invoked one of multiple times to export some userdata to XML.
+ * The \p buffer content of length \p length is stored with optional name
+ * \p name.
+ *
+ * When importing this XML file, the import() callback (if set) will be
+ * called exactly as many times as hwloc_export_obj_userdata() was called
+ * during export(). It will receive the corresponding \p name, \p buffer
+ * and \p length arguments.
+ *
+ * \note Only printable characters may be exported to XML string attributes.
+ * Any other character, especially any non-ASCII character, will be silently
+ * dropped.
+ *
+ */
+HWLOC_DECLSPEC void hwloc_export_obj_userdata(void *reserved, hwloc_topology_t topology, hwloc_obj_t obj, const char *name, const void *buffer, size_t length);
+
+/** \brief Set the application-specific callback for importing userdata
+ *
+ * On XML import, userdata is ignored by default because hwloc does not know
+ * how to store it in memory.
+ *
+ * This function lets applications set \p import to a callback function
+ * that will get the XML-stored userdata and store it in the object as expected
+ * by the application.
+ *
+ * \p import may be \c NULL if userdata should be ignored during import.
+ *
+ * \note This function should be called before hwloc_topology_load().
+ */
+HWLOC_DECLSPEC void hwloc_topology_set_userdata_import_callback(hwloc_topology_t topology,
+								void (*import)(hwloc_topology_t topology, hwloc_obj_t obj, const char *name, const void *buffer, size_t length));
+
 /** @} */