CORE-6004: Add a switch to disable the "TCP Loopback Fast Path" option (Windows only)

builds/install/misc/firebird.conf.in

@@ -768,6 +768,14 @@
 #
 #TcpNoNagle = 1
 
+#
+# Either enables or disables the "TCP Loopback Fast Path" feature (SIO_LOOPBACK_FAST_PATH).
+# Applies to Windows (version 8/2012 or higher) only.
+#
+# Type: Boolean, default 1 (true)
+#
+#TcpLoopbackFastPathOption = 1
+
 #
 # Allows setting of IPV6_V6ONLY socket option. If enabled, IPv6 sockets
 # allow only IPv6 communication and separate sockets must be used for

doc/Firebird_conf.txt

@@ -124,6 +124,7 @@ Only meaningful for Windows SS on SMP systems.
 OldParameterOrdering       boolean  default false
 TcpRemoteBufferSize        integer  default 8192 (bytes)
 TcpNoNagle                 boolean  default false
+TcpLoopbackFastPathOption  boolean  default true
 IpcMapSize                 integer  default 4096 (bytes)
 DefaultDbCachePages        integer  default SS: 2048. CS: 75
 ConnectionTimeout          integer  default 180 (seconds)

src/common/config/config.cpp

@@ -148,6 +148,7 @@ const Config::ConfigEntry Config::entries[MAX_CONFIG_KEY] =
 	{TYPE_INTEGER,		"CpuAffinityMask",			(ConfigValue) 0},
 	{TYPE_INTEGER,		"TcpRemoteBufferSize",		(ConfigValue) 8192},		// bytes
 	{TYPE_BOOLEAN,		"TcpNoNagle",				(ConfigValue) true},
+	{TYPE_BOOLEAN,		"TcpLoopbackFastPathOption",(ConfigValue) true},
 	{TYPE_INTEGER,		"DefaultDbCachePages",		(ConfigValue) -1},			// pages
 	{TYPE_INTEGER,		"ConnectionTimeout",		(ConfigValue) 180},			// seconds
 	{TYPE_INTEGER,		"DummyPacketInterval",		(ConfigValue) 0},			// seconds
@@ -492,6 +493,11 @@ bool Config::getTcpNoNagle() const
 	return get<bool>(KEY_TCP_NO_NAGLE);
 }
 
+bool Config::getTcpLoopbackFastPathOption() const
+{
+	return get<bool>(KEY_TCP_LOOPBACK_FAST_PATH_OPTION);
+}
+
 bool Config::getIPv6V6Only() const
 {
 	return get<bool>(KEY_IPV6_V6ONLY);

src/common/config/config.h

@@ -95,6 +95,7 @@ public:
 		KEY_CPU_AFFINITY_MASK,
 		KEY_TCP_REMOTE_BUFFER_SIZE,
 		KEY_TCP_NO_NAGLE,
+		KEY_TCP_LOOPBACK_FAST_PATH_OPTION,
 		KEY_DEFAULT_DB_CACHE_PAGES,
 		KEY_CONNECTION_TIMEOUT,
 		KEY_DUMMY_PACKET_INTERVAL,
@@ -252,6 +253,9 @@ public:
 	// Disable Nagle algorithm
 	bool getTcpNoNagle() const;
 
+	// Enable or disable the TCP Loopback Fast Path option
+	bool getTcpLoopbackFastPathOption() const;
+
 	// Let IPv6 socket accept only IPv6 packets
 	bool getIPv6V6Only() const;
 

src/remote/inet.cpp

@@ -3242,16 +3242,18 @@ static bool setNoNagleOption(rem_port* port)
 bool setFastLoopbackOption(SOCKET s)
 {
 #ifdef WIN_NT
-	int optval = 1;
-	DWORD bytes = 0;
+	if (Config::getDefaultConfig()->getTcpLoopbackFastPathOption())
+	{
+		int optval = 1;
+		DWORD bytes = 0;
 
-	int ret = WSAIoctl(s, SIO_LOOPBACK_FAST_PATH, &optval, sizeof(optval),
-					   NULL, 0, &bytes, 0, 0);
+		int ret = WSAIoctl(s, SIO_LOOPBACK_FAST_PATH, &optval, sizeof(optval),
+			NULL, 0, &bytes, 0, 0);
 
-	return (ret == 0);
-#else
-	return false;
+		return (ret == 0);
+	}
 #endif
+	return false;
 }
 
 void setStopMainThread(FPTR_INT func)