Fix a couple of issues in recent patch to print updates to postgresql.conf

settings: avoid calling superuser() in contexts where it's not defined,
don't leak the transient copies of GetConfigOption output, and avoid the
whole exercise in postmaster child processes.

I found that actually no current caller of GetConfigOption has any use for
its internal check of GUC_SUPERUSER_ONLY.  But rather than just remove
that entirely, it seemed better to add a parameter indicating whether to
enforce the check.

Per report from Simon and subsequent testing.

src/backend/utils/misc/guc-file.l

@@ -4,7 +4,7 @@
  *
  * Copyright (c) 2000-2009, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/backend/utils/misc/guc-file.l,v 1.61 2009/09/17 21:15:18 petere Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/misc/guc-file.l,v 1.62 2009/10/03 18:04:57 tgl Exp $
  */
 
 %{
@@ -312,21 +312,26 @@ ProcessConfigFile(GucContext context)
 	/* If we got here all the options checked out okay, so apply them. */
 	for (item = head; item; item = item->next)
 	{
-		char *pre_value = NULL;
+		char   *pre_value = NULL;
 
-		if (context == PGC_SIGHUP)
-			pre_value = pstrdup(GetConfigOption(item->name));
+		/* In SIGHUP cases in the postmaster, report changes */
+		if (context == PGC_SIGHUP && !IsUnderPostmaster)
+			pre_value = pstrdup(GetConfigOption(item->name, false));
 
 		if (set_config_option(item->name, item->value, context,
 			   					 PGC_S_FILE, GUC_ACTION_SET, true))
 		{
-			if (pre_value && strcmp(pre_value, GetConfigOption(item->name)) != 0)
+			set_config_sourcefile(item->name, item->filename,
+								  item->sourceline);
+			if (pre_value &&
+				strcmp(pre_value, GetConfigOption(item->name, false)) != 0)
 				ereport(elevel,
 						(errmsg("parameter \"%s\" changed to \"%s\"",
 								item->name, item->value)));
-			set_config_sourcefile(item->name, item->filename,
-								  item->sourceline);
 		}
+
+		if (pre_value)
+			pfree(pre_value);
 	}
 
 	/* Remember when we last successfully loaded the config file. */

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.519 2009/09/22 23:43:38 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.520 2009/10/03 18:04:57 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -5197,11 +5197,15 @@ SetConfigOption(const char *name, const char *value,
  * Fetch the current value of the option `name'. If the option doesn't exist,
  * throw an ereport and don't return.
  *
+ * If restrict_superuser is true, we also enforce that only superusers can
+ * see GUC_SUPERUSER_ONLY variables.  This should only be passed as true
+ * in user-driven calls.
+ *
  * The string is *not* allocated for modification and is really only
  * valid until the next call to configuration related functions.
  */
 const char *
-GetConfigOption(const char *name)
+GetConfigOption(const char *name, bool restrict_superuser)
 {
 	struct config_generic *record;
 	static char buffer[256];
@@ -5211,7 +5215,9 @@ GetConfigOption(const char *name)
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
 			   errmsg("unrecognized configuration parameter \"%s\"", name)));
-	if ((record->flags & GUC_SUPERUSER_ONLY) && !superuser())
+	if (restrict_superuser &&
+		(record->flags & GUC_SUPERUSER_ONLY) &&
+		!superuser())
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 				 errmsg("must be superuser to examine \"%s\"", name)));

src/include/utils/guc.h

@@ -7,7 +7,7 @@
  * Copyright (c) 2000-2009, PostgreSQL Global Development Group
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
- * $PostgreSQL: pgsql/src/include/utils/guc.h,v 1.105 2009/09/22 23:43:41 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/utils/guc.h,v 1.106 2009/10/03 18:04:57 tgl Exp $
  *--------------------------------------------------------------------
  */
 #ifndef GUC_H
@@ -249,7 +249,7 @@ extern void DefineCustomEnumVariable(
 
 extern void EmitWarningsOnPlaceholders(const char *className);
 
-extern const char *GetConfigOption(const char *name);
+extern const char *GetConfigOption(const char *name, bool restrict_superuser);
 extern const char *GetConfigOptionResetString(const char *name);
 extern void ProcessConfigFile(GucContext context);
 extern void InitializeGUCOptions(void);

src/timezone/pgtz.c

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/timezone/pgtz.c,v 1.63 2009/06/11 14:49:15 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/timezone/pgtz.c,v 1.64 2009/10/03 18:04:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1366,7 +1366,7 @@ pg_timezone_initialize(void)
 	pg_tz	   *def_tz = NULL;
 
 	/* Do we need to try to figure the session timezone? */
-	if (pg_strcasecmp(GetConfigOption("timezone"), "UNKNOWN") == 0)
+	if (pg_strcasecmp(GetConfigOption("timezone", false), "UNKNOWN") == 0)
 	{
 		/* Select setting */
 		def_tz = select_default_timezone();
@@ -1377,7 +1377,7 @@ pg_timezone_initialize(void)
 	}
 
 	/* What about the log timezone? */
-	if (pg_strcasecmp(GetConfigOption("log_timezone"), "UNKNOWN") == 0)
+	if (pg_strcasecmp(GetConfigOption("log_timezone", false), "UNKNOWN") == 0)
 	{
 		/* Select setting, but don't duplicate work */
 		if (!def_tz)