[PATCH bpf-next] bpf: guard bpf_get_current_cgroup_id() with CONFIG_CGROUPS

[Yonghong Song]

Commit bf6fa2c893c5 ("bpf: implement bpf_get_current_cgroup_id()
helper") introduced a new helper bpf_get_current_cgroup_id().
The helper has a dependency on CONFIG_CGROUPS.

When CONFIG_CGROUPS is not defined, using the helper will result
the following verifier error:
  kernel subsystem misconfigured func bpf_get_current_cgroup_id#80
which is hard for users to interpret.
Guarding the reference to bpf_get_current_cgroup_id_proto with
CONFIG_CGROUPS will result in below better message:
  unknown func bpf_get_current_cgroup_id#80

Fixes: bf6fa2c893c5 ("bpf: implement bpf_get_current_cgroup_id() helper")
Suggested-by: Daniel Borkmann <dan...@iogearbox.net>
Signed-off-by: Yonghong Song <y...@fb.com>
---
 kernel/trace/bpf_trace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index e2ab5b7..0ae6829 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -564,8 +564,10 @@ tracing_func_proto(enum bpf_func_id func_id, const struct 
bpf_prog *prog)
                return &bpf_get_prandom_u32_proto;
        case BPF_FUNC_probe_read_str:
                return &bpf_probe_read_str_proto;
+#ifdef CONFIG_CGROUPS
        case BPF_FUNC_get_current_cgroup_id:
                return &bpf_get_current_cgroup_id_proto;
+#endif
        default:
                return NULL;
        }
-- 
2.9.5