Phase 1 of fix for 'SMgrRelation hashtable corrupted' problem. This

is the minimum required fix.  I want to look next at taking advantage of
it by simplifying the message semantics in the shared inval message queue,
but that part can be held over for 8.1 if it turns out too ugly.

src/include/utils/rel.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/rel.h,v 1.81 2004/12/31 22:03:46 pgsql Exp $
+ * $PostgreSQL: pgsql/src/include/utils/rel.h,v 1.82 2005/01/10 20:02:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -233,6 +233,31 @@ typedef Relation *RelationPtr;
 #define RelationGetNamespace(relation) \
 	((relation)->rd_rel->relnamespace)
 
+/*
+ * RelationOpenSmgr
+ *		Open the relation at the smgr level, if not already done.
+ */
+#define RelationOpenSmgr(relation) \
+	do { \
+		if ((relation)->rd_smgr == NULL) \
+			smgrsetowner(&((relation)->rd_smgr), smgropen((relation)->rd_node)); \
+	} while (0)
+
+/*
+ * RelationCloseSmgr
+ *		Close the relation at the smgr level, if not already done.
+ *
+ * Note: smgrclose should unhook from owner pointer, hence the Assert.
+ */
+#define RelationCloseSmgr(relation) \
+	do { \
+		if ((relation)->rd_smgr != NULL) \
+		{ \
+			smgrclose((relation)->rd_smgr); \
+			Assert((relation)->rd_smgr == NULL); \
+		} \
+	} while (0)
+
 /*
  * RELATION_IS_LOCAL
  *		If a rel is either temp or newly created in the current transaction,