bpf-script-example.c

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/*
 * bpf-script-example.c
 * Test basic LLVM building
 */
#ifndef LINUX_VERSION_CODE
# error Need LINUX_VERSION_CODE
# error Example: for 4.2 kernel, put 'clang-opt="-DLINUX_VERSION_CODE=0x40200" into llvm section of ~/.perfconfig'
#endif
#define BPF_ANY 0
#define BPF_MAP_TYPE_ARRAY 2
#define BPF_FUNC_map_lookup_elem 1
#define BPF_FUNC_map_update_elem 2

static void *(*bpf_map_lookup_elem)(void *map, void *key) =
    (void *) BPF_FUNC_map_lookup_elem;
static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
    (void *) BPF_FUNC_map_update_elem;

struct bpf_map_def {
    unsigned int type;
    unsigned int key_size;
    unsigned int value_size;
    unsigned int max_entries;
};

#define SEC(NAME) __attribute__((section(NAME), used))
struct bpf_map_def SEC("maps") flip_table = {
    .type = BPF_MAP_TYPE_ARRAY,
    .key_size = sizeof(int),
    .value_size = sizeof(int),
    .max_entries = 1,
};

SEC("func=do_epoll_wait")
int bpf_func__SyS_epoll_pwait(void *ctx)
{
    int ind =0;
    int *flag = bpf_map_lookup_elem(&flip_table, &ind);
    int new_flag;
    if (!flag)
        return 0;
    /* flip flag and store back */
    new_flag = !*flag;
    bpf_map_update_elem(&flip_table, &ind, &new_flag, BPF_ANY);
    return new_flag;
}
char _license[] SEC("license") = "GPL";
int _version SEC("version") = LINUX_VERSION_CODE;