Re: [PATCH v3] cgroup/bpf: fast path skb BPF filtering

+static inline bool
+__cgroup_bpf_prog_array_is_empty(struct cgroup_bpf *cgrp_bpf,
+				 enum cgroup_bpf_attach_type type)
+{
+	struct bpf_prog_array *array = rcu_access_pointer(cgrp_bpf->effective[type]);
+
+	return array == &bpf_empty_prog_array.hdr;
+}
+
+#define CGROUP_BPF_TYPE_ENABLED(sk, atype)				       \
+({									       \
+	struct cgroup *__cgrp = sock_cgroup_ptr(&(sk)->sk_cgrp_data);	       \
+									       \
+	!__cgroup_bpf_prog_array_is_empty(&__cgrp->bpf, (atype));	       \
+})
+

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e7a163a3146b..0d2195c6fb2a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -1161,6 +1161,19 @@ struct bpf_prog_array {
 	struct bpf_prog_array_item items[];
 };
 
+struct bpf_empty_prog_array {
+	struct bpf_prog_array hdr;
+	struct bpf_prog *null_prog;
+};
+
+/* to avoid allocating empty bpf_prog_array for cgroups that
+ * don't have bpf program attached use one global 'bpf_empty_prog_array'
+ * It will not be modified the caller of bpf_prog_array_alloc()
+ * (since caller requested prog_cnt == 0)
+ * that pointer should be 'freed' by bpf_prog_array_free()
+ */
+extern struct bpf_empty_prog_array bpf_empty_prog_array;