Minimal hotplug support: provide a facility for notifying persistent

reference holders that their reference is about to become invalid.

src/include/gpxe/hotplug.h

@@ -0,0 +1,58 @@
+#ifndef _GPXE_HOTPLUG_H
+#define _GPXE_HOTPLUG_H
+
+/** @file
+ *
+ * Hotplug support
+ *
+ */
+
+#include <gpxe/list.h>
+
+/**
+ * A persistent reference to another data structure
+ *
+ * This data structure should be embedded within any data structure
+ * (the referrer) which holds a persistent reference to a separate,
+ * volatile data structure (the referee).
+ */
+struct reference {
+	/** List of persistent references */
+	struct list_head list;
+	/** Forget persistent reference
+	 *
+	 * @v ref		Persistent reference
+	 *
+	 * This method is called immediately before the referred-to
+	 * data structure is destroyed.  The reference holder must
+	 * forget all references to the referee before returning from
+	 * this method.
+	 *
+	 * This method must also call ref_del() to remove the
+	 * reference.
+	 */
+	void ( * forget ) ( struct reference *ref );
+};
+
+/**
+ * Add persistent reference
+ *
+ * @v ref		Persistent reference
+ * @v list		List of persistent references
+ */
+static inline void ref_add ( struct reference *ref, struct list_head *list ) {
+	list_add ( &ref->list, list );
+}
+
+/**
+ * Remove persistent reference
+ *
+ * @v ref		Persistent reference
+ */
+static inline void ref_del ( struct reference *ref ) {
+	list_del ( &ref->list );
+}
+
+extern void forget_references ( struct list_head *list );
+
+#endif /* _GPXE_HOTPLUG_H */