From bdf72b13775b7fa71d24a92c71fc0c4002109e01 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@otacoo.com>
Date: Mon, 29 Jun 2015 15:07:24 +0900
Subject: [PATCH 4/5] Extend pg_tablespace_location with option missing_ok

This is useful for code paths that prefer receive an empty response
instead of an ERROR if tablespace specified does not exist.
---
 doc/src/sgml/func.sgml        |  9 +++++++--
 src/backend/utils/adt/misc.c  | 30 ++++++++++++++++++++++++++----
 src/include/catalog/pg_proc.h |  2 ++
 src/include/utils/builtins.h  |  1 +
 4 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 80a4f26..0257df6 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -15850,9 +15850,14 @@ SELECT pg_type_is_visible('myschema.widget'::regtype);
        <entry>get the set of database OIDs that have objects in the tablespace</entry>
       </row>
       <row>
-       <entry><literal><function>pg_tablespace_location(<parameter>tablespace_oid</parameter>)</function></literal></entry>
+       <entry><literal><function>pg_tablespace_location(<parameter>tablespace_oid</parameter> [, <parameter>missing_ok</> <type>boolean</type>])</function></literal></entry>
        <entry><type>text</type></entry>
-       <entry>get the path in the file system that this tablespace is located in</entry>
+       <entry>
+        Get the path in the file system that this tablespace is located in.
+        If <parameter>missing_ok</> is <literal>true</>, the function returns
+        NULL when the tablespace does not exist. if <literal>false</>, an
+        error is raised. The default is <literal>false</>.
+       </entry>
       </row>
       <row>
        <entry><literal><function>pg_typeof(<parameter>any</parameter>)</function></literal></entry>
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index c0495d9..f5f61c5 100644
--- a/src/backend/utils/adt/misc.c
+++ b/src/backend/utils/adt/misc.c
@@ -347,6 +347,10 @@ pg_tablespace_location(PG_FUNCTION_ARGS)
 	char		sourcepath[MAXPGPATH];
 	char		targetpath[MAXPGPATH];
 	int			rllen;
+	bool		missing_ok = false;
+
+	if (PG_NARGS() == 2)
+		missing_ok = PG_GETARG_BOOL(1);

 	/*
 	 * It's useful to apply this function to pg_class.reltablespace, wherein
@@ -373,10 +377,15 @@ pg_tablespace_location(PG_FUNCTION_ARGS)

 	rllen = readlink(sourcepath, targetpath, sizeof(targetpath));
 	if (rllen < 0)
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read symbolic link \"%s\": %m",
-						sourcepath)));
+	{
+		if (missing_ok && errno == ENOENT)
+			PG_RETURN_NULL();
+		else
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read symbolic link \"%s\": %m",
+							sourcepath)));
+	}
 	if (rllen >= sizeof(targetpath))
 		ereport(ERROR,
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
@@ -394,6 +403,19 @@ pg_tablespace_location(PG_FUNCTION_ARGS)
 }

 /*
+ * pg_tablespace_location (1 argument version)
+ *
+ * note: this wrapper is necessary to pass the sanity check in opr_sanity,
+ * which checks that all built-in functions that share the implementing C
+ * function take the same number of arguments.
+ */
+Datum
+pg_tablespace_location_1arg(PG_FUNCTION_ARGS)
+{
+	return pg_tablespace_location(fcinfo);
+}
+
+/*
  * pg_sleep - delay for N seconds
  */
 Datum
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index f9c6176..6ccbf9b 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -2922,6 +2922,8 @@ DESCR("current trigger depth");

 DATA(insert OID = 3778 ( pg_tablespace_location PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 25 "26" _null_ _null_ _null_ _null_ _null_ pg_tablespace_location _null_ _null_ _null_ ));
 DESCR("tablespace location");
+DATA(insert OID = 3579 ( pg_tablespace_location PGNSP PGUID 12 1 0 0 0 f f f f t f s 2 0 25 "26 16" _null_ _null_ _null_ _null_ _null_ pg_tablespace_location_1arg _null_ _null_ _null_ ));
+DESCR("tablespace location");

 DATA(insert OID = 1946 (  encode						PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 25 "17 25" _null_ _null_ _null_ _null_ _null_ binary_encode _null_ _null_ _null_ ));
 DESCR("convert bytea value into some ascii-only text string");
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index 615e5ab..150afb6 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -490,6 +490,7 @@ extern Datum pg_terminate_backend(PG_FUNCTION_ARGS);
 extern Datum pg_reload_conf(PG_FUNCTION_ARGS);
 extern Datum pg_tablespace_databases(PG_FUNCTION_ARGS);
 extern Datum pg_tablespace_location(PG_FUNCTION_ARGS);
+extern Datum pg_tablespace_location_1arg(PG_FUNCTION_ARGS);
 extern Datum pg_rotate_logfile(PG_FUNCTION_ARGS);
 extern Datum pg_sleep(PG_FUNCTION_ARGS);
 extern Datum pg_get_keywords(PG_FUNCTION_ARGS);
-- 
2.4.5