[RFC PATCH bpf-next 4/5] selftests/bpf: Add new cgroup helper open_classid()

[Yafang Shao <laoar.shao@xxxxxxxxx>]

Add a new cgroup helper open_classid() to get the net_cls cgroup fd.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 tools/testing/selftests/bpf/cgroup_helpers.c | 16 ++++++++++++++++
 tools/testing/selftests/bpf/cgroup_helpers.h |  1 +
 2 files changed, 17 insertions(+)

diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c
index f68fbc6..2631efe 100644
--- a/tools/testing/selftests/bpf/cgroup_helpers.c
+++ b/tools/testing/selftests/bpf/cgroup_helpers.c
@@ -578,6 +578,22 @@ int join_classid(void)
 }
 
 /**
+ * open_classid() - Open a cgroupv1 net_cls classid
+ *
+ * This function expects the cgroup work dir to be already created, as we
+ * open it here.
+ *
+ * On success, it returns the file descriptor. On failure it returns -1.
+ */
+int open_classid(void)
+{
+	char cgroup_workdir[PATH_MAX + 1];
+
+	format_classid_path(cgroup_workdir);
+	return open(cgroup_workdir, O_RDONLY);
+}
+
+/**
  * cleanup_classid_environment() - Cleanup the cgroupv1 net_cls environment
  *
  * At call time, it moves the calling process to the root cgroup, and then
diff --git a/tools/testing/selftests/bpf/cgroup_helpers.h b/tools/testing/selftests/bpf/cgroup_helpers.h
index 5c2cb9c..ebc0513 100644
--- a/tools/testing/selftests/bpf/cgroup_helpers.h
+++ b/tools/testing/selftests/bpf/cgroup_helpers.h
@@ -31,6 +31,7 @@ int write_cgroup_file_parent(const char *relative_path, const char *file,
 /* cgroupv1 related */
 int set_classid(unsigned int id);
 int join_classid(void);
+int open_classid(void);
 
 int setup_classid_environment(void);
 void cleanup_classid_environment(void);
-- 
1.8.3.1