Extend object-access hook machinery to support post-alter events.

This also slightly widens the scope of what we support in terms of
post-create events.

KaiGai Kohei, with a few changes, mostly to the comments, by me

1 files changed, 48 insertions, 1 deletions

diff --git a/src/include/catalog/objectaccess.h b/src/include/catalog/objectaccess.h
index b9bb1bcd2f..25f963b074 100644
--- a/src/include/catalog/objectaccess.h
+++ b/src/include/catalog/objectaccess.h
@@ -22,6 +22,11 @@
  * OAT_DROP should be invoked just before deletion of objects; typically
  * deleteOneObject(). Its arguments are packed within ObjectAccessDrop.
  *
+ * OAT_POST_ALTER should be invoked just after the object is altered,
+ * but before the command counter is incremented.  An extension using the
+ * hook can use SnapshotNow and SnapshotSelf to get the old and new
+ * versions of the tuple.
+ *
  * Other types may be added in the future.
  */
 typedef enum ObjectAccessType
@@ -57,20 +62,51 @@ typedef struct
 } ObjectAccessDrop;
 
 /*
- * Hook, and a macro to invoke it.
+ * Arguments of OAT_POST_ALTER event
  */
+typedef struct
+{
+	/*
+	 * This identifier is used when system catalog takes two IDs
+	 * to identify a particular tuple of the catalog.
+	 * It is only used when the caller want to identify an entry
+	 * of pg_inherits, pg_db_role_setting or pg_user_mapping.
+	 * Elsewhere, InvalidOid should be set.
+	 */
+	Oid			auxiliary_id;
+
+	/*
+	 * If this flag is set, the user hasn't requested that the object be
+	 * altered, but we're doing it anyway for some internal reason.
+	 * Permissions-checking hooks may want to skip checks if, say, we're
+	 * alter the constraints of a temporary heap during CLUSTER.
+	 */
+	bool		is_internal;
+} ObjectAccessPostAlter;
+
+/* Plugin provides a hook function matching this signature. */
 typedef void (*object_access_hook_type) (ObjectAccessType access,
 													 Oid classId,
 													 Oid objectId,
 													 int subId,
 													 void *arg);
 
+/* Plugin sets this variable to a suitable hook function. */
 extern PGDLLIMPORT object_access_hook_type object_access_hook;
 
+/* Core code uses these functions to call the hook (see macros below). */
 extern void RunObjectPostCreateHook(Oid classId, Oid objectId, int subId,
 									bool is_internal);
 extern void RunObjectDropHook(Oid classId, Oid objectId, int subId,
 							  int dropflags);
+extern void RunObjectPostAlterHook(Oid classId, Oid objectId, int subId,
+								   Oid auxiliaryId, bool is_internal);
+
+/*
+ * The following macros are wrappers around the functions above; these should
+ * normally be used to invoke the hook in lieu of calling the above functions
+ * directly.
+ */
 
 #define InvokeObjectPostCreateHook(classId,objectId,subId)			\
 	InvokeObjectPostCreateHookArg((classId),(objectId),(subId),false)
@@ -90,4 +126,15 @@ extern void RunObjectDropHook(Oid classId, Oid objectId, int subId,
 							  (dropflags));							\
 	} while(0)
 
+#define InvokeObjectPostAlterHook(classId,objectId,subId)			\
+	InvokeObjectPostAlterHookArg((classId),(objectId),(subId),		\
+								 InvalidOid,false)
+#define InvokeObjectPostAlterHookArg(classId,objectId,subId,		\
+									 auxiliaryId,is_internal)		\
+	do {															\
+		if (object_access_hook)										\
+			RunObjectPostAlterHook((classId),(objectId),(subId),	\
+								   (auxiliaryId),(is_internal));	\
+	} while(0)
+
 #endif   /* OBJECTACCESS_H */