1 files changed, 66 insertions, 0 deletions
diff --git a/examples/bpf/bpf_graft.c b/examples/bpf/bpf_graft.c
new file mode 100644
index 0000000..8066dcc
--- /dev/null
+++ b/examples/bpf/bpf_graft.c
@@ -0,0 +1,66 @@
+#include "../../include/bpf_api.h"
+
+/* This example demonstrates how classifier run-time behaviour
+ * can be altered with tail calls. We start out with an empty
+ * jmp_tc array, then add section aaa to the array slot 0, and
+ * later on atomically replace it with section bbb. Note that
+ * as shown in other examples, the tc loader can prepopulate
+ * tail called sections, here we start out with an empty one
+ * on purpose to show it can also be done this way.
+ *
+ * tc filter add dev foo parent ffff: bpf obj graft.o
+ * tc exec bpf dbg
+ *   [...]
+ *   Socket Thread-20229 [001] ..s. 138993.003923: : fallthrough
+ *   <idle>-0            [001] ..s. 138993.202265: : fallthrough
+ *   Socket Thread-20229 [001] ..s. 138994.004149: : fallthrough
+ *   [...]
+ *
+ * tc exec bpf graft m:globals/jmp_tc key 0 obj graft.o sec aaa
+ * tc exec bpf dbg
+ *   [...]
+ *   Socket Thread-19818 [002] ..s. 139012.053587: : aaa
+ *   <idle>-0            [002] ..s. 139012.172359: : aaa
+ *   Socket Thread-19818 [001] ..s. 139012.173556: : aaa
+ *   [...]
+ *
+ * tc exec bpf graft m:globals/jmp_tc key 0 obj graft.o sec bbb
+ * tc exec bpf dbg
+ *   [...]
+ *   Socket Thread-19818 [002] ..s. 139022.102967: : bbb
+ *   <idle>-0            [002] ..s. 139022.155640: : bbb
+ *   Socket Thread-19818 [001] ..s. 139022.156730: : bbb
+ *   [...]
+ */
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(key_size, sizeof(uint32_t));
+	__uint(value_size, sizeof(uint32_t));
+	__uint(max_entries, 1);
+	__uint(pinning, LIBBPF_PIN_BY_NAME);
+} jmp_tc __section(".maps");
+
+__section("aaa")
+int cls_aaa(struct __sk_buff *skb)
+{
+	printt("aaa\n");
+	return TC_H_MAKE(1, 42);
+}
+
+__section("bbb")
+int cls_bbb(struct __sk_buff *skb)
+{
+	printt("bbb\n");
+	return TC_H_MAKE(1, 43);
+}
+
+__section_cls_entry
+int cls_entry(struct __sk_buff *skb)
+{
+	tail_call(skb, &jmp_tc, 0);
+	printt("fallthrough\n");
+	return BPF_H_DEFAULT;
+}
+
+BPF_LICENSE("GPL");