Implement an API to let foreign-data wrappers actually be functional.

This commit provides the core code and documentation needed.  A contrib
module test case will follow shortly.

Shigeru Hanada, Jan Urbanski, Heikki Linnakangas

src/include/foreign/fdwapi.h

@@ -0,0 +1,98 @@
+/*-------------------------------------------------------------------------
+ *
+ * fdwapi.h
+ *	  API for foreign-data wrappers
+ *
+ * Copyright (c) 2010-2011, PostgreSQL Global Development Group
+ *
+ * src/include/foreign/fdwapi.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef FDWAPI_H
+#define FDWAPI_H
+
+#include "nodes/execnodes.h"
+#include "nodes/relation.h"
+
+/* To avoid including explain.h here, reference ExplainState thus: */
+struct ExplainState;
+
+
+/*
+ * FdwPlan is the information returned to the planner by PlanForeignScan.
+ */
+typedef struct FdwPlan
+{
+	NodeTag		type;
+
+	/*
+	 * Cost estimation info. The startup_cost is time before retrieving
+	 * the first row, so it should include costs of connecting to the remote
+	 * host, sending over the query, etc.  Note that PlanForeignScan also
+	 * ought to set baserel->rows and baserel->width if it can produce any
+	 * usable estimates of those values.
+	 */
+	Cost		startup_cost;	/* cost expended before fetching any tuples */
+	Cost		total_cost;		/* total cost (assuming all tuples fetched) */
+
+	/*
+	 * FDW private data, which will be available at execution time.
+	 *
+	 * Note that everything in this list must be copiable by copyObject().
+	 * One way to store an arbitrary blob of bytes is to represent it as a
+	 * bytea Const.  Usually, though, you'll be better off choosing a
+	 * representation that can be dumped usefully by nodeToString().
+	 */
+	List	   *fdw_private;
+} FdwPlan;
+
+
+/*
+ * Callback function signatures --- see fdwhandler.sgml for more info.
+ */
+
+typedef FdwPlan * (*PlanForeignScan_function) (Oid foreigntableid,
+											   PlannerInfo *root,
+											   RelOptInfo *baserel);
+
+typedef void (*ExplainForeignScan_function) (ForeignScanState *node,
+											 struct ExplainState *es);
+
+typedef void (*BeginForeignScan_function) (ForeignScanState *node,
+										   int eflags);
+
+typedef TupleTableSlot * (*IterateForeignScan_function) (ForeignScanState *node);
+
+typedef void (*ReScanForeignScan_function) (ForeignScanState *node);
+
+typedef void (*EndForeignScan_function) (ForeignScanState *node);
+
+
+/*
+ * FdwRoutine is the struct returned by a foreign-data wrapper's handler
+ * function.  It provides pointers to the callback functions needed by the
+ * planner and executor.
+ *
+ * Currently, all functions must be supplied.  Later there may be optional
+ * additions.  It's recommended that the handler initialize the struct with
+ * makeNode(FdwRoutine) so that all fields are set to zero.
+ */
+typedef struct FdwRoutine
+{
+	NodeTag		type;
+
+	PlanForeignScan_function PlanForeignScan;
+	ExplainForeignScan_function ExplainForeignScan;
+	BeginForeignScan_function BeginForeignScan;
+	IterateForeignScan_function IterateForeignScan;
+	ReScanForeignScan_function ReScanForeignScan;
+	EndForeignScan_function EndForeignScan;
+} FdwRoutine;
+
+
+/* Functions in foreign/foreign.c */
+extern FdwRoutine *GetFdwRoutine(Oid fdwhandler);
+extern FdwRoutine *GetFdwRoutineByRelId(Oid relid);
+
+#endif   /* FDWAPI_H */

src/include/foreign/foreign.h

@@ -60,6 +60,13 @@ typedef struct UserMapping
 	List	   *options;		/* useoptions as DefElem list */
 } UserMapping;
 
+typedef struct ForeignTable
+{
+	Oid			relid;			/* relation Oid */
+	Oid			serverid;		/* server Oid */
+	List	   *options;		/* ftoptions as DefElem list */
+} ForeignTable;
+
 
 extern ForeignServer *GetForeignServer(Oid serverid);
 extern ForeignServer *GetForeignServerByName(const char *name, bool missing_ok);
@@ -69,5 +76,6 @@ extern ForeignDataWrapper *GetForeignDataWrapper(Oid fdwid);
 extern ForeignDataWrapper *GetForeignDataWrapperByName(const char *name,
 							bool missing_ok);
 extern Oid	GetForeignDataWrapperOidByName(const char *name, bool missing_ok);
+extern ForeignTable *GetForeignTable(Oid relid);
 
 #endif   /* FOREIGN_H */