Rationalize common/relpath.[hc].

Commit a73018392636ce832b09b5c31f6ad1f18a4643ea created rather a mess by
putting dependencies on backend-only include files into include/common.
We really shouldn't do that.  To clean it up:

* Move TABLESPACE_VERSION_DIRECTORY back to its longtime home in
catalog/catalog.h.  We won't consider this symbol part of the FE/BE API.

* Push enum ForkNumber from relfilenode.h into relpath.h.  We'll consider
relpath.h as the source of truth for fork numbers, since relpath.c was
already partially serving that function, and anyway relfilenode.h was
kind of a random place for that enum.

* So, relfilenode.h now includes relpath.h rather than vice-versa.  This
direction of dependency is fine.  (That allows most, but not quite all,
of the existing explicit #includes of relpath.h to go away again.)

* Push forkname_to_number from catalog.c to relpath.c, just to centralize
fork number stuff a bit better.

* Push GetDatabasePath from catalog.c to relpath.c; it was rather odd
that the previous commit didn't keep this together with relpath().

* To avoid needing relfilenode.h in common/, redefine the underlying
function (now called GetRelationPath) as taking separate OID arguments,
and make the APIs using RelFileNode or RelFileNodeBackend into macro
wrappers.  (The macros have a potential multiple-eval risk, but none of
the existing call sites have an issue with that; one of them had such a
risk already anyway.)

* Fix failure to follow the directions when "init" fork type was added;
specifically, the errhint in forkname_to_number wasn't updated, and neither
was the SGML documentation for pg_relation_size().

* Fix tablespace-path-too-long check in CreateTableSpace() to account for
fork-name component of maximum-length pathnames.  This requires putting
FORKNAMECHARS into a header file, but it was rather useless (and
actually unreferenced) where it was.

The last couple of items are potentially back-patchable bug fixes,
if anyone is sufficiently excited about them; but personally I'm not.

Per a gripe from Christoph Berg about how include/common wasn't
self-contained.

20 files changed, 162 insertions, 153 deletions

diff --git a/src/backend/access/rmgrdesc/smgrdesc.c b/src/backend/access/rmgrdesc/smgrdesc.c
index 2e451a9ea8d..aa72d4c4c3a 100644
--- a/src/backend/access/rmgrdesc/smgrdesc.c
+++ b/src/backend/access/rmgrdesc/smgrdesc.c
@@ -16,7 +16,6 @@
 
 #include "catalog/catalog.h"
 #include "catalog/storage_xlog.h"
-#include "common/relpath.h"
 
 
 void
diff --git a/src/backend/access/rmgrdesc/xactdesc.c b/src/backend/access/rmgrdesc/xactdesc.c
index e8fabc174e2..7c43d4c06fd 100644
--- a/src/backend/access/rmgrdesc/xactdesc.c
+++ b/src/backend/access/rmgrdesc/xactdesc.c
@@ -16,7 +16,6 @@
 
 #include "access/xact.h"
 #include "catalog/catalog.h"
-#include "common/relpath.h"
 #include "storage/sinval.h"
 #include "utils/timestamp.h"
 
diff --git a/src/backend/access/rmgrdesc/xlogdesc.c b/src/backend/access/rmgrdesc/xlogdesc.c
index cc9a472e1fa..e3d7b6681f3 100644
--- a/src/backend/access/rmgrdesc/xlogdesc.c
+++ b/src/backend/access/rmgrdesc/xlogdesc.c
@@ -17,7 +17,6 @@
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
 #include "catalog/pg_control.h"
-#include "common/relpath.h"
 #include "utils/guc.h"
 #include "utils/timestamp.h"
 
diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index 05e74de9211..b7829ff4c6d 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -20,7 +20,6 @@
 #include "access/xlog.h"
 #include "access/xlogutils.h"
 #include "catalog/catalog.h"
-#include "common/relpath.h"
 #include "storage/smgr.h"
 #include "utils/guc.h"
 #include "utils/hsearch.h"
diff --git a/src/backend/catalog/catalog.c b/src/backend/catalog/catalog.c
index 282e0b9ae8c..3ec360c2be5 100644
--- a/src/backend/catalog/catalog.c
+++ b/src/backend/catalog/catalog.c
@@ -37,7 +37,6 @@
 #include "catalog/pg_shseclabel.h"
 #include "catalog/pg_tablespace.h"
 #include "catalog/toasting.h"
-#include "common/relpath.h"
 #include "miscadmin.h"
 #include "storage/fd.h"
 #include "utils/fmgroids.h"
@@ -45,56 +44,6 @@
 #include "utils/tqual.h"
 
 
-
-/*
- * forkname_to_number - look up fork number by name
- */
-ForkNumber
-forkname_to_number(char *forkName)
-{
-	ForkNumber	forkNum;
-
-	for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
-		if (strcmp(forkNames[forkNum], forkName) == 0)
-			return forkNum;
-
-	ereport(ERROR,
-			(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-			 errmsg("invalid fork name"),
-			 errhint("Valid fork names are \"main\", \"fsm\", and \"vm\".")));
-	return InvalidForkNumber;	/* keep compiler quiet */
-}
-
-/*
- * GetDatabasePath			- construct path to a database dir
- *
- * Result is a palloc'd string.
- *
- * XXX this must agree with relpath()!
- */
-char *
-GetDatabasePath(Oid dbNode, Oid spcNode)
-{
-	if (spcNode == GLOBALTABLESPACE_OID)
-	{
-		/* Shared system relations live in {datadir}/global */
-		Assert(dbNode == 0);
-		return pstrdup("global");
-	}
-	else if (spcNode == DEFAULTTABLESPACE_OID)
-	{
-		/* The default tablespace is {datadir}/base */
-		return psprintf("base/%u", dbNode);
-	}
-	else
-	{
-		/* All other tablespaces are accessed via symlinks */
-		return psprintf("pg_tblspc/%u/%s/%u",
-						spcNode, TABLESPACE_VERSION_DIRECTORY, dbNode);
-	}
-}
-
-
 /*
  * IsSystemRelation
  *		True iff the relation is either a system catalog or toast table.
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index f5ae98ff80e..619aa78d809 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -51,7 +51,6 @@
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
 #include "commands/typecmds.h"
-#include "common/relpath.h"
 #include "executor/executor.h"
 #include "foreign/foreign.h"
 #include "miscadmin.h"
diff --git a/src/backend/commands/tablespace.c b/src/backend/commands/tablespace.c
index 9421dc2e4e0..357e6e19741 100644
--- a/src/backend/commands/tablespace.c
+++ b/src/backend/commands/tablespace.c
@@ -68,7 +68,6 @@
 #include "commands/tablecmds.h"
 #include "commands/tablespace.h"
 #include "commands/user.h"
-#include "common/relpath.h"
 #include "miscadmin.h"
 #include "postmaster/bgwriter.h"
 #include "storage/fd.h"
@@ -278,11 +277,11 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 
 	/*
 	 * Check that location isn't too long. Remember that we're going to append
-	 * 'PG_XXX/<dboid>/<relid>.<nnn>'.	FYI, we never actually reference the
-	 * whole path, but mkdir() uses the first two parts.
+	 * 'PG_XXX/<dboid>/<relid>_<fork>.<nnn>'.  FYI, we never actually
+	 * reference the whole path here, but mkdir() uses the first two parts.
 	 */
 	if (strlen(location) + 1 + strlen(TABLESPACE_VERSION_DIRECTORY) + 1 +
-		OIDCHARS + 1 + OIDCHARS + 1 + OIDCHARS > MAXPGPATH)
+		OIDCHARS + 1 + OIDCHARS + 1 + FORKNAMECHARS + 1 + OIDCHARS > MAXPGPATH)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 				 errmsg("tablespace location \"%s\" is too long",
diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index f611f591b61..42e66f2fed7 100644
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -18,8 +18,8 @@
 #include <time.h>
 
 #include "access/xlog_internal.h"		/* for pg_start/stop_backup */
+#include "catalog/catalog.h"
 #include "catalog/pg_type.h"
-#include "common/relpath.h"
 #include "lib/stringinfo.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 4493930eda0..a89099b5036 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -50,28 +50,20 @@
 #include <unistd.h>
 #include <sys/stat.h>
 
-#include "miscadmin.h"
-
 #include "access/rewriteheap.h"
 #include "access/transam.h"
 #include "access/tuptoaster.h"
 #include "access/xact.h"
-
 #include "catalog/catalog.h"
-
-#include "common/relpath.h"
-
 #include "lib/binaryheap.h"
-
+#include "miscadmin.h"
 #include "replication/logical.h"
 #include "replication/reorderbuffer.h"
 #include "replication/slot.h"
 #include "replication/snapbuild.h" /* just for SnapBuildSnapDecRefcount */
-
 #include "storage/bufmgr.h"
 #include "storage/fd.h"
 #include "storage/sinval.h"
-
 #include "utils/builtins.h"
 #include "utils/combocid.h"
 #include "utils/memdebug.h"
@@ -80,6 +72,7 @@
 #include "utils/relfilenodemap.h"
 #include "utils/tqual.h"
 
+
 /* entry for a hash table we use to map from xid to our transaction state */
 typedef struct ReorderBufferTXNByIdEnt
 {
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 4e46ddbba29..246f31bfe14 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -35,7 +35,6 @@
 
 #include "catalog/catalog.h"
 #include "catalog/storage.h"
-#include "common/relpath.h"
 #include "executor/instrument.h"
 #include "miscadmin.h"
 #include "pg_trace.h"
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 054aff717c7..62adc1ce6ba 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -16,7 +16,6 @@
 #include "postgres.h"
 
 #include "catalog/catalog.h"
-#include "common/relpath.h"
 #include "executor/instrument.h"
 #include "storage/buf_internals.h"
 #include "storage/bufmgr.h"
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 42dbe87ca4b..0560bf9d72b 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -71,7 +71,6 @@
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/pg_tablespace.h"
-#include "common/relpath.h"
 #include "pgstat.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 8133a337f7b..921861b0bd5 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -28,7 +28,6 @@
 #include "miscadmin.h"
 #include "access/xlog.h"
 #include "catalog/catalog.h"
-#include "common/relpath.h"
 #include "portability/instr_time.h"
 #include "postmaster/bgwriter.h"
 #include "storage/fd.h"
diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index 78fe4688226..68ab0e19061 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -21,7 +21,6 @@
 #include "catalog/pg_tablespace.h"
 #include "commands/dbcommands.h"
 #include "commands/tablespace.h"
-#include "common/relpath.h"
 #include "miscadmin.h"
 #include "storage/fd.h"
 #include "utils/acl.h"
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index e3893db6585..241f738d608 100644
--- a/src/backend/utils/adt/misc.c
+++ b/src/backend/utils/adt/misc.c
@@ -25,7 +25,6 @@
 #include "catalog/pg_tablespace.h"
 #include "catalog/pg_type.h"
 #include "commands/dbcommands.h"
-#include "common/relpath.h"
 #include "funcapi.h"
 #include "miscadmin.h"
 #include "parser/keywords.h"
diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index c8cea028d4e..c947bff4fca 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -56,7 +56,6 @@
 #include "catalog/schemapg.h"
 #include "catalog/storage.h"
 #include "commands/trigger.h"
-#include "common/relpath.h"
 #include "miscadmin.h"
 #include "optimizer/clauses.h"
 #include "optimizer/planmain.h"
diff --git a/src/common/relpath.c b/src/common/relpath.c
index fbb5de6922b..fc8b2732eaa 100644
--- a/src/common/relpath.c
+++ b/src/common/relpath.c
@@ -1,6 +1,8 @@
 /*-------------------------------------------------------------------------
  * relpath.c
- *		Shared frontend/backend code to find out pathnames of relation files
+ *		Shared frontend/backend code to compute pathnames of relation files
+ *
+ * This module also contains some logic associated with fork names.
  *
  * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -16,18 +18,18 @@
 #include "postgres_fe.h"
 #endif
 
+#include "catalog/catalog.h"
 #include "catalog/pg_tablespace.h"
 #include "common/relpath.h"
 #include "storage/backendid.h"
 
-#define FORKNAMECHARS	4		/* max chars for a fork name */
 
 /*
  * Lookup table of fork name by fork number.
  *
- * If you add a new entry, remember to update the errhint below, and the
- * documentation for pg_relation_size(). Also keep FORKNAMECHARS above
- * up-to-date.
+ * If you add a new entry, remember to update the errhint in
+ * forkname_to_number() below, and update the SGML documentation for
+ * pg_relation_size().
  */
 const char *const forkNames[] = {
 	"main",						/* MAIN_FORKNUM */
@@ -37,6 +39,32 @@ const char *const forkNames[] = {
 };
 
 /*
+ * forkname_to_number - look up fork number by name
+ *
+ * In backend, we throw an error for no match; in frontend, we just
+ * return InvalidForkNumber.
+ */
+ForkNumber
+forkname_to_number(const char *forkName)
+{
+	ForkNumber	forkNum;
+
+	for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
+		if (strcmp(forkNames[forkNum], forkName) == 0)
+			return forkNum;
+
+#ifndef FRONTEND
+	ereport(ERROR,
+			(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+			 errmsg("invalid fork name"),
+			 errhint("Valid fork names are \"main\", \"fsm\", "
+					 "\"vm\", and \"init\".")));
+#endif
+
+	return InvalidForkNumber;
+}
+
+/*
  * forkname_chars
  *		We use this to figure out whether a filename could be a relation
  *		fork (as opposed to an oddly named stray file that somehow ended
@@ -63,80 +91,117 @@ forkname_chars(const char *str, ForkNumber *fork)
 			return len;
 		}
 	}
+	if (fork)
+		*fork = InvalidForkNumber;
 	return 0;
 }
 
+
+/*
+ * GetDatabasePath - construct path to a database directory
+ *
+ * Result is a palloc'd string.
+ *
+ * XXX this must agree with GetRelationPath()!
+ */
+char *
+GetDatabasePath(Oid dbNode, Oid spcNode)
+{
+	if (spcNode == GLOBALTABLESPACE_OID)
+	{
+		/* Shared system relations live in {datadir}/global */
+		Assert(dbNode == 0);
+		return pstrdup("global");
+	}
+	else if (spcNode == DEFAULTTABLESPACE_OID)
+	{
+		/* The default tablespace is {datadir}/base */
+		return psprintf("base/%u", dbNode);
+	}
+	else
+	{
+		/* All other tablespaces are accessed via symlinks */
+		return psprintf("pg_tblspc/%u/%s/%u",
+						spcNode, TABLESPACE_VERSION_DIRECTORY, dbNode);
+	}
+}
+
 /*
- * relpathbackend - construct path to a relation's file
+ * GetRelationPath - construct path to a relation's file
  *
  * Result is a palloc'd string.
+ *
+ * Note: ideally, backendId would be declared as type BackendId, but relpath.h
+ * would have to include a backend-only header to do that; doesn't seem worth
+ * the trouble considering BackendId is just int anyway.
  */
 char *
-relpathbackend(RelFileNode rnode, BackendId backend, ForkNumber forknum)
+GetRelationPath(Oid dbNode, Oid spcNode, Oid relNode,
+				int backendId, ForkNumber forkNumber)
 {
 	char	   *path;
 
-	if (rnode.spcNode == GLOBALTABLESPACE_OID)
+	if (spcNode == GLOBALTABLESPACE_OID)
 	{
 		/* Shared system relations live in {datadir}/global */
-		Assert(rnode.dbNode == 0);
-		Assert(backend == InvalidBackendId);
-		if (forknum != MAIN_FORKNUM)
+		Assert(dbNode == 0);
+		Assert(backendId == InvalidBackendId);
+		if (forkNumber != MAIN_FORKNUM)
 			path = psprintf("global/%u_%s",
-					 rnode.relNode, forkNames[forknum]);
+							relNode, forkNames[forkNumber]);
 		else
-			path = psprintf("global/%u", rnode.relNode);
+			path = psprintf("global/%u", relNode);
 	}
-	else if (rnode.spcNode == DEFAULTTABLESPACE_OID)
+	else if (spcNode == DEFAULTTABLESPACE_OID)
 	{
 		/* The default tablespace is {datadir}/base */
-		if (backend == InvalidBackendId)
+		if (backendId == InvalidBackendId)
 		{
-			if (forknum != MAIN_FORKNUM)
+			if (forkNumber != MAIN_FORKNUM)
 				path = psprintf("base/%u/%u_%s",
-						 rnode.dbNode, rnode.relNode,
-						 forkNames[forknum]);
+								dbNode, relNode,
+								forkNames[forkNumber]);
 			else
 				path = psprintf("base/%u/%u",
-						 rnode.dbNode, rnode.relNode);
+								dbNode, relNode);
 		}
 		else
 		{
-			if (forknum != MAIN_FORKNUM)
+			if (forkNumber != MAIN_FORKNUM)
 				path = psprintf("base/%u/t%d_%u_%s",
-						 rnode.dbNode, backend, rnode.relNode,
-						 forkNames[forknum]);
+								dbNode, backendId, relNode,
+								forkNames[forkNumber]);
 			else
 				path = psprintf("base/%u/t%d_%u",
-						 rnode.dbNode, backend, rnode.relNode);
+								dbNode, backendId, relNode);
 		}
 	}
 	else
 	{
 		/* All other tablespaces are accessed via symlinks */
-		if (backend == InvalidBackendId)
+		if (backendId == InvalidBackendId)
 		{
-			if (forknum != MAIN_FORKNUM)
+			if (forkNumber != MAIN_FORKNUM)
 				path = psprintf("pg_tblspc/%u/%s/%u/%u_%s",
-						 rnode.spcNode, TABLESPACE_VERSION_DIRECTORY,
-						 rnode.dbNode, rnode.relNode,
-						 forkNames[forknum]);
+								spcNode, TABLESPACE_VERSION_DIRECTORY,
+								dbNode, relNode,
+								forkNames[forkNumber]);
 			else
 				path = psprintf("pg_tblspc/%u/%s/%u/%u",
-						 rnode.spcNode, TABLESPACE_VERSION_DIRECTORY,
-						 rnode.dbNode, rnode.relNode);
+								spcNode, TABLESPACE_VERSION_DIRECTORY,
+								dbNode, relNode);
 		}
 		else
 		{
-			if (forknum != MAIN_FORKNUM)
+			if (forkNumber != MAIN_FORKNUM)
 				path = psprintf("pg_tblspc/%u/%s/%u/t%d_%u_%s",
-						 rnode.spcNode, TABLESPACE_VERSION_DIRECTORY,
-						 rnode.dbNode, backend, rnode.relNode,
-						 forkNames[forknum]);
+								spcNode, TABLESPACE_VERSION_DIRECTORY,
+								dbNode, backendId, relNode,
+								forkNames[forkNumber]);
 			else
 				path = psprintf("pg_tblspc/%u/%s/%u/t%d_%u",
-						 rnode.spcNode, TABLESPACE_VERSION_DIRECTORY,
-						 rnode.dbNode, backend, rnode.relNode);
+								spcNode, TABLESPACE_VERSION_DIRECTORY,
+								dbNode, backendId, relNode);
 		}
 	}
 	return path;
diff --git a/src/include/catalog/catalog.h b/src/include/catalog/catalog.h
index 534a0815920..9d63ac22c8e 100644
--- a/src/include/catalog/catalog.h
+++ b/src/include/catalog/catalog.h
@@ -14,13 +14,17 @@
 #ifndef CATALOG_H
 #define CATALOG_H
 
+/*
+ *	'pgrminclude ignore' needed here because CppAsString2() does not throw
+ *	an error if the symbol is not defined.
+ */
+#include "catalog/catversion.h" /* pgrminclude ignore */
 #include "catalog/pg_class.h"
-#include "storage/relfilenode.h"
 #include "utils/relcache.h"
 
-extern ForkNumber forkname_to_number(char *forkName);
-
-extern char *GetDatabasePath(Oid dbNode, Oid spcNode);
+#define OIDCHARS		10		/* max chars printed by %u */
+#define TABLESPACE_VERSION_DIRECTORY	"PG_" PG_MAJORVERSION "_" \
+									CppAsString2(CATALOG_VERSION_NO)
 
 
 extern bool IsSystemRelation(Relation relation);
diff --git a/src/include/common/relpath.h b/src/include/common/relpath.h
index 23a226d058e..cdd9316f08b 100644
--- a/src/include/common/relpath.h
+++ b/src/include/common/relpath.h
@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * relpath.h
- *		Declarations for relpath() and friends
+ *		Declarations for GetRelationPath() and friends
  *
  * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -14,29 +14,61 @@
 #define RELPATH_H
 
 /*
- *	'pgrminclude ignore' needed here because CppAsString2() does not throw
- *	an error if the symbol is not defined.
+ * Stuff for fork names.
+ *
+ * The physical storage of a relation consists of one or more forks.
+ * The main fork is always created, but in addition to that there can be
+ * additional forks for storing various metadata. ForkNumber is used when
+ * we need to refer to a specific fork in a relation.
  */
-#include "catalog/catversion.h" /* pgrminclude ignore */
-#include "storage/relfilenode.h"
+typedef enum ForkNumber
+{
+	InvalidForkNumber = -1,
+	MAIN_FORKNUM = 0,
+	FSM_FORKNUM,
+	VISIBILITYMAP_FORKNUM,
+	INIT_FORKNUM
+
+	/*
+	 * NOTE: if you add a new fork, change MAX_FORKNUM and possibly
+	 * FORKNAMECHARS below, and update the forkNames array in
+	 * src/common/relpath.c
+	 */
+} ForkNumber;
 
+#define MAX_FORKNUM		INIT_FORKNUM
 
-#define OIDCHARS		10		/* max chars printed by %u */
-#define TABLESPACE_VERSION_DIRECTORY	"PG_" PG_MAJORVERSION "_" \
-									CppAsString2(CATALOG_VERSION_NO)
+#define FORKNAMECHARS	4		/* max chars for a fork name */
 
 extern const char *const forkNames[];
 
+extern ForkNumber forkname_to_number(const char *forkName);
 extern int	forkname_chars(const char *str, ForkNumber *fork);
-extern char *relpathbackend(RelFileNode rnode, BackendId backend,
-			   ForkNumber forknum);
 
-/* First argument is a RelFileNodeBackend */
-#define relpath(rnode, forknum) \
-		relpathbackend((rnode).node, (rnode).backend, (forknum))
+/*
+ * Stuff for computing filesystem pathnames for relations.
+ */
+extern char *GetDatabasePath(Oid dbNode, Oid spcNode);
+
+extern char *GetRelationPath(Oid dbNode, Oid spcNode, Oid relNode,
+				int backendId, ForkNumber forkNumber);
+
+/*
+ * Wrapper macros for GetRelationPath.	Beware of multiple
+ * evaluation of the RelFileNode or RelFileNodeBackend argument!
+ */
+
+/* First argument is a RelFileNode */
+#define relpathbackend(rnode, backend, forknum) \
+	GetRelationPath((rnode).dbNode, (rnode).spcNode, (rnode).relNode, \
+					backend, forknum)
 
 /* First argument is a RelFileNode */
 #define relpathperm(rnode, forknum) \
-		relpathbackend((rnode), InvalidBackendId, (forknum))
+	relpathbackend(rnode, InvalidBackendId, forknum)
+
+/* First argument is a RelFileNodeBackend */
+#define relpath(rnode, forknum) \
+	relpathbackend((rnode).node, (rnode).backend, forknum)
 
 #endif   /* RELPATH_H */
diff --git a/src/include/storage/relfilenode.h b/src/include/storage/relfilenode.h
index 8616bd3a1ec..d5b772ca9f6 100644
--- a/src/include/storage/relfilenode.h
+++ b/src/include/storage/relfilenode.h
@@ -14,31 +14,10 @@
 #ifndef RELFILENODE_H
 #define RELFILENODE_H
 
+#include "common/relpath.h"
 #include "storage/backendid.h"
 
 /*
- * The physical storage of a relation consists of one or more forks. The
- * main fork is always created, but in addition to that there can be
- * additional forks for storing various metadata. ForkNumber is used when
- * we need to refer to a specific fork in a relation.
- */
-typedef enum ForkNumber
-{
-	InvalidForkNumber = -1,
-	MAIN_FORKNUM = 0,
-	FSM_FORKNUM,
-	VISIBILITYMAP_FORKNUM,
-	INIT_FORKNUM
-
-	/*
-	 * NOTE: if you add a new fork, change MAX_FORKNUM below and update the
-	 * forkNames array in src/common/relpath.c
-	 */
-} ForkNumber;
-
-#define MAX_FORKNUM		INIT_FORKNUM
-
-/*
  * RelFileNode must provide all that we need to know to physically access
  * a relation, with the exception of the backend ID, which can be provided
  * separately. Note, however, that a "physical" relation is comprised of