tools build: Add test for setns()

And provide an alternative implementation to keep perf building on older
distros as we're about to add initial support for namespaces.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Krister Johansen <kjlx@templeofstupid.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-bqdwijunhjlvps1ardykhw1i@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/Makefile.feature

@@ -64,7 +64,8 @@ FEATURE_TESTS_BASIC :=                  \
         get_cpuid                       \
         bpf                             \
         sched_getcpu			\
-        sdt
+        sdt				\
+        setns
 
 # FEATURE_TESTS_BASIC + FEATURE_TESTS_EXTRA is the complete list
 # of all feature tests

tools/build/feature/Makefile

@@ -49,7 +49,8 @@ FILES=                                          \
          test-sdt.bin                           \
          test-cxx.bin                           \
          test-jvmti.bin				\
-         test-sched_getcpu.bin
+         test-sched_getcpu.bin			\
+         test-setns.bin
 
 FILES := $(addprefix $(OUTPUT),$(FILES))
 
@@ -95,6 +96,9 @@ $(OUTPUT)test-glibc.bin:
 $(OUTPUT)test-sched_getcpu.bin:
 	$(BUILD)
 
+$(OUTPUT)test-setns.bin:
+	$(BUILD)
+
 DWARFLIBS := -ldw
 ifeq ($(findstring -static,${LDFLAGS}),-static)
 DWARFLIBS += -lelf -lebl -lz -llzma -lbz2

tools/build/feature/test-all.c

@@ -153,6 +153,10 @@
 # include "test-sdt.c"
 #undef main
 
+#define main main_test_setns
+# include "test-setns.c"
+#undef main
+
 int main(int argc, char *argv[])
 {
 	main_test_libpython();
@@ -188,6 +192,7 @@ int main(int argc, char *argv[])
 	main_test_libcrypto();
 	main_test_sched_getcpu();
 	main_test_sdt();
+	main_test_setns();
 
 	return 0;
 }

tools/build/feature/test-setns.c

@@ -0,0 +1,7 @@
+#define _GNU_SOURCE
+#include <sched.h>
+
+int main(void)
+{
+	return setns(0, 0);
+}