selftests/bpf: test_progs: add test__join_cgroup helper

test__join_cgroup() combines the following operations that usually
go hand in hand and returns cgroup fd:

  * setup cgroup environment (make sure cgroupfs is mounted)
  * mkdir cgroup
  * join cgroup

It also marks a test as a "cgroup cleanup needed" and removes cgroup
state after the test is done.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/Makefile

@@ -106,7 +106,7 @@ $(OUTPUT)/test_socket_cookie: cgroup_helpers.c
 $(OUTPUT)/test_sockmap: cgroup_helpers.c
 $(OUTPUT)/test_tcpbpf_user: cgroup_helpers.c
 $(OUTPUT)/test_tcpnotify_user: cgroup_helpers.c trace_helpers.c
-$(OUTPUT)/test_progs: trace_helpers.c
+$(OUTPUT)/test_progs: cgroup_helpers.c trace_helpers.c
 $(OUTPUT)/get_cgroup_id_user: cgroup_helpers.c
 $(OUTPUT)/test_cgroup_storage: cgroup_helpers.c
 $(OUTPUT)/test_netcnt: cgroup_helpers.c
@@ -200,7 +200,7 @@ $(ALU32_BUILD_DIR)/test_progs_32: test_progs.c $(OUTPUT)/libbpf.a\
 						| $(ALU32_BUILD_DIR)
 	$(CC) $(TEST_PROGS_CFLAGS) $(CFLAGS) \
 		-o $(ALU32_BUILD_DIR)/test_progs_32 \
-		test_progs.c test_stub.c trace_helpers.c prog_tests/*.c \
+		test_progs.c test_stub.c cgroup_helpers.c trace_helpers.c prog_tests/*.c \
 		$(OUTPUT)/libbpf.a $(LDLIBS)
 
 $(ALU32_BUILD_DIR)/test_progs_32: $(PROG_TESTS_H)

tools/testing/selftests/bpf/test_progs.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2017 Facebook
  */
 #include "test_progs.h"
+#include "cgroup_helpers.h"
 #include "bpf_rlimit.h"
 #include <argp.h>
 #include <string.h>
@@ -17,6 +18,7 @@ struct prog_test_def {
 	int error_cnt;
 	int skip_cnt;
 	bool tested;
+	bool need_cgroup_cleanup;
 
 	const char *subtest_name;
 	int subtest_num;
@@ -122,6 +124,39 @@ void test__fail(void)
 	env.test->error_cnt++;
 }
 
+int test__join_cgroup(const char *path)
+{
+	int fd;
+
+	if (!env.test->need_cgroup_cleanup) {
+		if (setup_cgroup_environment()) {
+			fprintf(stderr,
+				"#%d %s: Failed to setup cgroup environment\n",
+				env.test->test_num, env.test->test_name);
+			return -1;
+		}
+
+		env.test->need_cgroup_cleanup = true;
+	}
+
+	fd = create_and_get_cgroup(path);
+	if (fd < 0) {
+		fprintf(stderr,
+			"#%d %s: Failed to create cgroup '%s' (errno=%d)\n",
+			env.test->test_num, env.test->test_name, path, errno);
+		return fd;
+	}
+
+	if (join_cgroup(path)) {
+		fprintf(stderr,
+			"#%d %s: Failed to join cgroup '%s' (errno=%d)\n",
+			env.test->test_num, env.test->test_name, path, errno);
+		return -1;
+	}
+
+	return fd;
+}
+
 struct ipv4_packet pkt_v4 = {
 	.eth.h_proto = __bpf_constant_htons(ETH_P_IP),
 	.iph.ihl = 5,
@@ -530,6 +565,9 @@ int main(int argc, char **argv)
 		fprintf(env.stdout, "#%d %s:%s\n",
 			test->test_num, test->test_name,
 			test->error_cnt ? "FAIL" : "OK");
+
+		if (test->need_cgroup_cleanup)
+			cleanup_cgroup_environment();
 	}
 	stdio_restore();
 	printf("Summary: %d/%d PASSED, %d SKIPPED, %d FAILED\n",

tools/testing/selftests/bpf/test_progs.h

@@ -71,6 +71,7 @@ extern void test__force_log();
 extern bool test__start_subtest(const char *name);
 extern void test__skip(void);
 extern void test__fail(void);
+extern int test__join_cgroup(const char *path);
 
 #define MAGIC_BYTES 123