116 lines
2.9 KiB
C
116 lines
2.9 KiB
C
#include <linux/bpf.h>
|
|
|
|
#include "bpf_funcs.h"
|
|
|
|
#define ENTRY_INIT 3
|
|
#define ENTRY_0 0
|
|
#define ENTRY_1 1
|
|
#define MAX_JMP_SIZE 2
|
|
|
|
#define FOO 42
|
|
#define BAR 43
|
|
|
|
/* This example doesn't really do anything useful, but it's purpose is to
|
|
* demonstrate eBPF tail calls on a very simple example.
|
|
*
|
|
* cls_entry() is our classifier entry point, from there we jump based on
|
|
* skb->hash into cls_case1() or cls_case2(). They are both part of the
|
|
* program array jmp_tc. Indicated via __section_tail(), the tc loader
|
|
* populates the program arrays with the loaded file descriptors already.
|
|
*
|
|
* To demonstrate nested jumps, cls_case2() jumps within the same jmp_tc
|
|
* array to cls_case1(). And whenever we arrive at cls_case1(), we jump
|
|
* into cls_exit(), part of the jump array jmp_ex.
|
|
*
|
|
* Also, to show it's possible, all programs share map_sh and dump the value
|
|
* that the entry point incremented. The sections that are loaded into a
|
|
* program array can be atomically replaced during run-time, e.g. to change
|
|
* classifier behaviour.
|
|
*/
|
|
struct bpf_elf_map __section("maps") map_sh = {
|
|
.type = BPF_MAP_TYPE_ARRAY,
|
|
.size_key = sizeof(int),
|
|
.size_value = sizeof(int),
|
|
.pinning = PIN_OBJECT_NS,
|
|
.max_elem = 1,
|
|
};
|
|
|
|
struct bpf_elf_map __section("maps") jmp_tc = {
|
|
.type = BPF_MAP_TYPE_PROG_ARRAY,
|
|
.id = FOO,
|
|
.size_key = sizeof(int),
|
|
.size_value = sizeof(int),
|
|
.pinning = PIN_OBJECT_NS,
|
|
.max_elem = MAX_JMP_SIZE,
|
|
};
|
|
|
|
struct bpf_elf_map __section("maps") jmp_ex = {
|
|
.type = BPF_MAP_TYPE_PROG_ARRAY,
|
|
.id = BAR,
|
|
.size_key = sizeof(int),
|
|
.size_value = sizeof(int),
|
|
.pinning = PIN_OBJECT_NS,
|
|
.max_elem = 1,
|
|
};
|
|
|
|
__section_tail(FOO, ENTRY_0) int cls_case1(struct __sk_buff *skb)
|
|
{
|
|
char fmt[] = "case1: map-val: %d from:%u\n";
|
|
int key = 0, *val;
|
|
|
|
val = bpf_map_lookup_elem(&map_sh, &key);
|
|
if (val)
|
|
bpf_printk(fmt, sizeof(fmt), *val, skb->cb[0]);
|
|
|
|
skb->cb[0] = ENTRY_0;
|
|
bpf_tail_call(skb, &jmp_ex, ENTRY_0);
|
|
return 0;
|
|
}
|
|
|
|
__section_tail(FOO, ENTRY_1) int cls_case2(struct __sk_buff *skb)
|
|
{
|
|
char fmt[] = "case2: map-val: %d from:%u\n";
|
|
int key = 0, *val;
|
|
|
|
val = bpf_map_lookup_elem(&map_sh, &key);
|
|
if (val)
|
|
bpf_printk(fmt, sizeof(fmt), *val, skb->cb[0]);
|
|
|
|
skb->cb[0] = ENTRY_1;
|
|
bpf_tail_call(skb, &jmp_tc, ENTRY_0);
|
|
return 0;
|
|
}
|
|
|
|
__section_tail(BAR, ENTRY_0) int cls_exit(struct __sk_buff *skb)
|
|
{
|
|
char fmt[] = "exit: map-val: %d from:%u\n";
|
|
int key = 0, *val;
|
|
|
|
val = bpf_map_lookup_elem(&map_sh, &key);
|
|
if (val)
|
|
bpf_printk(fmt, sizeof(fmt), *val, skb->cb[0]);
|
|
|
|
/* Termination point. */
|
|
return -1;
|
|
}
|
|
|
|
__section("classifier") int cls_entry(struct __sk_buff *skb)
|
|
{
|
|
char fmt[] = "fallthrough\n";
|
|
int key = 0, *val;
|
|
|
|
/* For transferring state, we can use skb->cb[0] ... skb->cb[4]. */
|
|
val = bpf_map_lookup_elem(&map_sh, &key);
|
|
if (val) {
|
|
__sync_fetch_and_add(val, 1);
|
|
|
|
skb->cb[0] = ENTRY_INIT;
|
|
bpf_tail_call(skb, &jmp_tc, skb->hash & (MAX_JMP_SIZE - 1));
|
|
}
|
|
|
|
bpf_printk(fmt, sizeof(fmt));
|
|
return 0;
|
|
}
|
|
|
|
char __license[] __section("license") = "GPL";
|