1 #include "../../include/bpf_api.h"
2
3 /* This example demonstrates how classifier run-time behaviour
4 * can be altered with tail calls. We start out with an empty
5 * jmp_tc array, then add section aaa to the array slot 0, and
6 * later on atomically replace it with section bbb. Note that
7 * as shown in other examples, the tc loader can prepopulate
8 * tail called sections, here we start out with an empty one
9 * on purpose to show it can also be done this way.
10 *
11 * tc filter add dev foo parent ffff: bpf obj graft.o
12 * tc exec bpf dbg
13 * [...]
14 * Socket Thread-20229 [001] ..s. 138993.003923: : fallthrough
15 * <idle>-0 [001] ..s. 138993.202265: : fallthrough
16 * Socket Thread-20229 [001] ..s. 138994.004149: : fallthrough
17 * [...]
18 *
19 * tc exec bpf graft m:globals/jmp_tc key 0 obj graft.o sec aaa
20 * tc exec bpf dbg
21 * [...]
22 * Socket Thread-19818 [002] ..s. 139012.053587: : aaa
23 * <idle>-0 [002] ..s. 139012.172359: : aaa
24 * Socket Thread-19818 [001] ..s. 139012.173556: : aaa
25 * [...]
26 *
27 * tc exec bpf graft m:globals/jmp_tc key 0 obj graft.o sec bbb
28 * tc exec bpf dbg
29 * [...]
30 * Socket Thread-19818 [002] ..s. 139022.102967: : bbb
31 * <idle>-0 [002] ..s. 139022.155640: : bbb
32 * Socket Thread-19818 [001] ..s. 139022.156730: : bbb
33 * [...]
34 */
35
36 struct bpf_elf_map __section_maps jmp_tc = {
37 .type = BPF_MAP_TYPE_PROG_ARRAY,
38 .size_key = sizeof(uint32_t),
39 .size_value = sizeof(uint32_t),
40 .pinning = PIN_GLOBAL_NS,
41 .max_elem = 1,
42 };
43
44 __section("aaa")
cls_aaa(struct __sk_buff * skb)45 int cls_aaa(struct __sk_buff *skb)
46 {
47 printt("aaa\n");
48 return TC_H_MAKE(1, 42);
49 }
50
51 __section("bbb")
cls_bbb(struct __sk_buff * skb)52 int cls_bbb(struct __sk_buff *skb)
53 {
54 printt("bbb\n");
55 return TC_H_MAKE(1, 43);
56 }
57
58 __section_cls_entry
cls_entry(struct __sk_buff * skb)59 int cls_entry(struct __sk_buff *skb)
60 {
61 tail_call(skb, &jmp_tc, 0);
62 printt("fallthrough\n");
63 return BPF_H_DEFAULT;
64 }
65
66 BPF_LICENSE("GPL");
67