Minimal hotplug support: provide a facility for notifying persistent

reference holders that their reference is about to become invalid.

src/core/hotplug.c

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <assert.h>
+#include <gpxe/hotplug.h>
+
+/** @file
+ *
+ * Hotplug support
+ *
+ */
+
+/**
+ * Forget all persistent references to an object
+ *
+ * @v list		List of persistent references
+ */
+void forget_references ( struct list_head *list ) {
+	struct reference *ref;
+	struct reference *ref_tmp;
+
+	list_for_each_entry_safe ( ref, ref_tmp, list, list ) {
+		ref->forget ( ref );
+	}
+
+	/* The list had really better be empty by now, otherwise we're
+	 * screwed.
+	 */
+	assert ( list_empty ( list ) );
+}

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 */