examples/bpf/bpf_graft.c

   1 #include <linux/bpf.h>
   2
   3 #include "bpf_funcs.h"
   4
   5 /* This example demonstrates how classifier run-time behaviour
   6  * can be altered with tail calls. We start out with an empty
   7  * jmp_tc array, then add section aaa to the array slot 0, and
   8  * later on atomically replace it with section bbb. Note that
   9  * as shown in other examples, the tc loader can prepopulate
  10  * tail called sections, here we start out with an empty one
  11  * on purpose to show it can also be done this way.
  12  *
  13  * tc filter add dev foo parent ffff: bpf obj graft.o
  14  * tc exec bpf dbg
  15  *   [...]
  16  *   Socket Thread-20229 [001] ..s. 138993.003923: : fallthrough
  17  *   <idle>-0            [001] ..s. 138993.202265: : fallthrough
  18  *   Socket Thread-20229 [001] ..s. 138994.004149: : fallthrough
  19  *   [...]
  20  *
  21  * tc exec bpf graft m:globals/jmp_tc key 0 obj graft.o sec aaa
  22  * tc exec bpf dbg
  23  *   [...]
  24  *   Socket Thread-19818 [002] ..s. 139012.053587: : aaa
  25  *   <idle>-0            [002] ..s. 139012.172359: : aaa
  26  *   Socket Thread-19818 [001] ..s. 139012.173556: : aaa
  27  *   [...]
  28  *
  29  * tc exec bpf graft m:globals/jmp_tc key 0 obj graft.o sec bbb
  30  * tc exec bpf dbg
  31  *   [...]
  32  *   Socket Thread-19818 [002] ..s. 139022.102967: : bbb
  33  *   <idle>-0            [002] ..s. 139022.155640: : bbb
  34  *   Socket Thread-19818 [001] ..s. 139022.156730: : bbb
  35  *   [...]
  36  */
  37 struct bpf_elf_map __section("maps") jmp_tc = {
  38         .type           = BPF_MAP_TYPE_PROG_ARRAY,
  39         .size_key       = sizeof(int),
  40         .size_value     = sizeof(int),
  41         .pinning        = PIN_GLOBAL_NS,
  42         .max_elem       = 1,
  43 };
  44
  45 __section("aaa") int cls_aaa(struct __sk_buff *skb)
  46 {
  47         char fmt[] = "aaa\n";
  48
  49         bpf_printk(fmt, sizeof(fmt));
  50         return -1;
  51 }
  52
  53 __section("bbb") int cls_bbb(struct __sk_buff *skb)
  54 {
  55         char fmt[] = "bbb\n";
  56
  57         bpf_printk(fmt, sizeof(fmt));
  58         return -1;
  59 }
  60
  61 __section("classifier") int cls_entry(struct __sk_buff *skb)
  62 {
  63         char fmt[] = "fallthrough\n";
  64
  65         bpf_tail_call(skb, &jmp_tc, 0);
  66         bpf_printk(fmt, sizeof(fmt));
  67         return -1;
  68 }
  69
  70 char __license[] __section("license") = "GPL";