tools/testing/selftests/bpf/sockmap_tcp_msg_prog.c

#include <linux/bpf.h>
#include "bpf_helpers.h"
#include "bpf_util.h"
#include "bpf_endian.h"

int _version SEC("version") = 1;

#define bpf_printk(fmt, ...)					\
({								\
	       char ____fmt[] = fmt;				\
	       bpf_trace_printk(____fmt, sizeof(____fmt),	\
				##__VA_ARGS__);			\
})

SEC("sk_msg1")
int bpf_prog1(struct sk_msg_md *msg)
{
	void *data_end = (void *)(long) msg->data_end;
	void *data = (void *)(long) msg->data;

	char *d;

	if (data + 8 > data_end)
		return SK_DROP;

	bpf_printk("data length %i\n", (__u64)msg->data_end - (__u64)msg->data);
	d = (char *)data;
	bpf_printk("hello sendmsg hook %i %i\n", d[0], d[1]);

	return SK_PASS;
}

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