From 95bcf47ff9b8073faea99ea9bd65a7119ea4ee41 Mon Sep 17 00:00:00 2001
From: Bob Halley <source@isc.org>
Date: Sat, 19 Dec 1998 00:13:59 +0000
Subject: [PATCH] exists policy

---
 bin/tests/sym_test.c | 18 ++++++++++++++----
 lib/isc/symtab.c     | 28 ++++++++++++++++++++--------
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/bin/tests/sym_test.c b/bin/tests/sym_test.c
index 36f039c114..fca2a2258e 100644
--- a/bin/tests/sym_test.c
+++ b/bin/tests/sym_test.c
@@ -15,6 +15,8 @@
  * SOFTWARE.
  */
 
+#include <config.h>
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -41,7 +43,7 @@ mem_strdup(isc_mem_t *mctx, const char *s) {
 
 static void
 undefine_action(char *key, unsigned int type, isc_symvalue_t value) {
-	INSIST(type == 0);
+	INSIST(type == 1);
 	isc_mem_free(mctx, key);
 	isc_mem_free(mctx, value.as_pointer);
 }
@@ -54,16 +56,23 @@ main(int argc, char *argv[]) {
 	isc_symvalue_t value;
 	int trace = 0;
 	int c;
+	isc_symexists_t exists_policy = isc_symexists_reject;
 
 	INSIST(isc_mem_create(0, 0, &mctx) == ISC_R_SUCCESS);
 	INSIST(isc_symtab_create(mctx, 691, undefine_action, &st) ==
 	       ISC_R_SUCCESS);
 
-	while ((c = getopt(argc, argv, "t")) != -1) {
+	while ((c = getopt(argc, argv, "tar")) != -1) {
 		switch (c) {
 		case 't':
 			trace = 1;
 			break;
+		case 'a':
+			exists_policy = isc_symexists_add;
+			break;
+		case 'r':
+			exists_policy = isc_symexists_replace;
+			break;
 		}
 	}
 
@@ -74,7 +83,7 @@ main(int argc, char *argv[]) {
 
 		if (cp[0] == '!') {
 			cp++;
-			result = isc_symtab_undefine(st, cp, 0);
+			result = isc_symtab_undefine(st, cp, 1);
 			if (trace || result != ISC_R_SUCCESS)
 				printf("undefine('%s'): %s\n", cp,
 				       isc_result_totext(result));
@@ -97,7 +106,8 @@ main(int argc, char *argv[]) {
 				*cp++ = '\0';
 				key = mem_strdup(mctx, key);
 				value.as_pointer = mem_strdup(mctx, cp);
-				result = isc_symtab_define(st, key, 0, value);
+				result = isc_symtab_define(st, key, 1, value,
+							   exists_policy);
 				if (trace || result != ISC_R_SUCCESS)
 					printf("define('%s', '%s'): %s\n",
 					       key, cp,
diff --git a/lib/isc/symtab.c b/lib/isc/symtab.c
index 6c6188cbba..45297411c5 100644
--- a/lib/isc/symtab.c
+++ b/lib/isc/symtab.c
@@ -168,7 +168,7 @@ isc_symtab_lookup(isc_symtab_t *symtab, const char *key, unsigned int type,
 
 isc_result_t
 isc_symtab_define(isc_symtab_t *symtab, char *key, unsigned int type,
-		  isc_symvalue_t value)
+		  isc_symvalue_t value, isc_symexists_t exists_policy)
 {
 	unsigned int bucket;
 	elt_t *elt;
@@ -178,17 +178,29 @@ isc_symtab_define(isc_symtab_t *symtab, char *key, unsigned int type,
 
 	FIND(symtab, key, type, bucket, elt);
 
-	if (elt != NULL)
-		return (ISC_R_EXISTS);
-
-	elt = (elt_t *)isc_mem_get(symtab->mctx, sizeof *elt);
-	if (elt == NULL)
-		return (ISC_R_NOMEMORY);
+	if (exists_policy != isc_symexists_add && elt != NULL) {
+		if (exists_policy == isc_symexists_reject)
+			return (ISC_R_EXISTS);
+		INSIST(exists_policy == isc_symexists_replace);
+		UNLINK(symtab->table[bucket], elt, link);
+		if (symtab->undefine_action != NULL)
+			(symtab->undefine_action)(elt->key, elt->type,
+						  elt->value);
+	} else {
+		elt = (elt_t *)isc_mem_get(symtab->mctx, sizeof *elt);
+		if (elt == NULL)
+			return (ISC_R_NOMEMORY);
+	}
 	elt->key = key;
 	elt->type = type;
 	elt->value = value;
 
-	APPEND(symtab->table[bucket], elt, link);
+	/*
+	 * We prepend so that a 'type 0' lookup will return the most
+	 * recent definition, and a 'type 0' undefine will undefine the
+	 * most recent definition.
+	 */
+	PREPEND(symtab->table[bucket], elt, link);
 
 	return (ISC_R_SUCCESS);
 }