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 <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Krister Johansen <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/build/Makefile.feature

···
         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

···
          test-sdt.bin                           \
          test-cxx.bin                           \
          test-jvmti.bin				\
-         test-sched_getcpu.bin
+         test-sched_getcpu.bin			\
+         test-setns.bin
 
 FILES := $(addprefix $(OUTPUT),$(FILES))
 
···
 	$(BUILD)
 
 $(OUTPUT)test-sched_getcpu.bin:
+	$(BUILD)
+
+$(OUTPUT)test-setns.bin:
 	$(BUILD)
 
 DWARFLIBS := -ldw

tools/build/feature/test-all.c

···
 # 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();
···
 	main_test_libcrypto();
 	main_test_sched_getcpu();
 	main_test_sdt();
+	main_test_setns();
 
 	return 0;
 }

tools/build/feature/test-setns.c

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

tools/perf/Makefile.config

···
   CFLAGS += -DHAVE_SCHED_GETCPU_SUPPORT
 endif
 
+ifeq ($(feature-setns), 1)
+  CFLAGS += -DHAVE_SETNS_SUPPORT
+  $(call detected,CONFIG_SETNS)
+endif
+
 ifndef NO_LIBELF
   CFLAGS += -DHAVE_LIBELF_SUPPORT
   EXTLIBS += -lelf

tools/perf/util/Build

···
 libperf-y += symbol-minimal.o
 endif
 
+ifndef CONFIG_SETNS
+libperf-y += setns.o
+endif
+
 libperf-$(CONFIG_DWARF) += probe-finder.o
 libperf-$(CONFIG_DWARF) += dwarf-aux.o
 libperf-$(CONFIG_DWARF) += dwarf-regs.o

tools/perf/util/setns.c

···
+#include "util.h"
+#include <unistd.h>
+#include <sys/syscall.h>
+
+int setns(int fd, int nstype)
+{
+	return syscall(__NR_setns, fd, nstype);
+}

tools/perf/util/util.h

···
 int sched_getcpu(void);
 #endif
 
+#ifndef HAVE_SETNS_SUPPORT
+int setns(int fd, int nstype);
+#endif
+
 #endif /* GIT_COMPAT_UTIL_H */