make: Introduce compile time include/config.h generation

It's being reported that some systems (as Ubuntu 13.04) already
have struct tcp_repair_opt definition in their system headers.

| sk-tcp.c:25:8: error: redefinition of struct tcp_repair_opt
| sk-tcp.c:31:2: error: redeclaration of enumerator TCP_NO_QUEUE

So add a facility for compile time testing for reported entities
to be present on a system. For this we generate include/config.h
where all tested entries will lay and source code need to include
it only in places where really needed.
Reported-by: Vasily Averin <vvs@parallels.com>
Acked-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

Makefile

@@ -17,6 +17,7 @@ export VERSION_MAJOR VERSION_MINOR VERSION_SUBLEVEL VERSION_EXTRA VERSION_NAME
 #MAKEFLAGS := -r -R
 
 include Makefile.inc
+include Makefile.config
 
 #
 # Common definitions
@@ -118,7 +119,7 @@ ifeq ($(GCOV),1)
 %.o $(PROGRAM): override CFLAGS += --coverage
 endif
 
-all: pie $(VERSION_HEADER)
+all: config pie $(VERSION_HEADER)
 	$(Q) $(MAKE) $(PROGRAM)
 
 protobuf/%::
@@ -158,6 +159,7 @@ clean-built:
 	$(Q) $(MAKE) $(build)=pie clean
 	$(Q) $(MAKE) $(build-crtools)=. clean
 	$(Q) $(MAKE) -C Documentation clean
+	$(Q) $(RM) ./include/config.h
 	$(Q) $(RM) ./$(PROGRAM)
 
 rebuild: clean-built

Makefile.config

+include scripts/utilities.mak
+include scripts/feature-tests.mak
+
+CONFIG		:= include/config.h
+
+$(CONFIG): scripts/utilities.mak scripts/feature-tests.mak
+	$(E) "  GEN     " $@
+	$(Q) @echo '#ifndef __CR_CONFIG_H__' > $@
+	$(Q) @echo '#define __CR_CONFIG_H__' >> $@
+ifeq ($(call try-cc,$(TCP_REPAIR_TEST),,),y)
+	$(Q) @echo '#define CONFIG_HAS_TCP_REPAIR' >> $@
+endif
+	$(Q) @echo '#endif /* __CR_CONFIG_H__ */' >> $@
+
+config: $(CONFIG)
+
+.PHONY: config

scripts/feature-tests.mak

+define TCP_REPAIR_TEST
+
+#include <netinet/tcp.h>
+
+int main(void)
+{
+	struct tcp_repair_opt opts;
+	opts.opt_code = TCP_NO_QUEUE;
+	opts.opt_val = 0;
+
+	return opts.opt_val;
+}
+endef

sk-tcp.c

@@ -18,10 +18,19 @@
 #include "netfilter.h"
 #include "image.h"
 #include "namespaces.h"
+#include "config.h"
 
 #include "protobuf.h"
 #include "protobuf/tcp-stream.pb-c.h"
 
+#ifndef CONFIG_HAS_TCP_REPAIR
+/*
+ * It's been reported that both tcp_repair_opt
+ * and TCP_ enum already shipped in netinet/tcp.h
+ * system header by some distros thus we need a
+ * test if we can use predefined ones or provide
+ * our own.
+ */
 struct tcp_repair_opt {
 	u32	opt_code;
 	u32	opt_val;
@@ -33,6 +42,7 @@ enum {
 	TCP_SEND_QUEUE,
 	TCP_QUEUES_NR,
 };
+#endif
 
 #ifndef TCP_TIMESTAMP
 #define TCP_TIMESTAMP	24