xdp

#include "vmlinux.h"
#include <bpf/bpf_helpers.h>

SEC("xdp")
int xdp_pass(struct xdp_md *ctx)
{
	void *data = (void *)(long)ctx->data;
	void *data_end = (void *)(long)ctx->data_end;
	int pkt_sz = data_end - data;

	bpf_printk("packet size: %d", pkt_sz);
	return XDP_PASS;
}

char __license[] SEC("license") = "GPL";

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <sys/resource.h>
#include <bpf/libbpf.h>
#include "xdppass.skel.h"

static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
{
	return vfprintf(stderr, format, args);
}

static volatile sig_atomic_t stop;

static void sig_int(int signo)
{
	stop = 1;
}

int main(int argc, char ** argv)
{
    struct xdppass_bpf *skel = NULL;
    int err;
    int ifindex = 0;

    /* Set up libbpf errors and debug info callback */
	libbpf_set_print(libbpf_print_fn);

    if(argc > 1)
        ifindex = atoi(argv[1]);

    /* Open load and verify BPF application */
    skel = xdppass_bpf__open_and_load();
    if (!skel) {
		fprintf(stderr, "Failed to open BPF skeleton\n");
		return 1;
	}
    
    skel->links.xdp_pass = bpf_program__attach_xdp(skel->progs.xdp_pass, ifindex);
    if (!skel->links.xdp_pass) {
		err = -errno;
		fprintf(stderr, "Failed to attach XDP program to ifindex %d\n", ifindex);
		goto cleanup;
	}

    err = xdppass_bpf__attach(skel);
	if (err) {
		fprintf(stderr, "Failed to auto-attach BPF skeleton: %d\n", err);
		goto cleanup;
	}

    if (signal(SIGINT, sig_int) == SIG_ERR) {
		fprintf(stderr, "can't set signal handler: %s\n", strerror(errno));
		goto cleanup;
	}

    printf("Successfully started! Please run `sudo cat /sys/kernel/debug/tracing/trace_pipe` "
	       "to see output of the BPF programs.\n");

    while (!stop) {
		fprintf(stderr, ".");
		sleep(1);
	}

cleanup:
    xdppass_bpf__destroy(skel);
    return -err;
}