int bpf_link_create()

in contrib/libbpf/src/bpf.c [672:771]

• 81 lines of code
• 29 McCabe index (conditional complexity)

int bpf_link_create(int prog_fd, int target_fd,
		    enum bpf_attach_type attach_type,
		    const struct bpf_link_create_opts *opts)
{
	const size_t attr_sz = offsetofend(union bpf_attr, link_create);
	__u32 target_btf_id, iter_info_len;
	union bpf_attr attr;
	int fd, err;

	if (!OPTS_VALID(opts, bpf_link_create_opts))
		return libbpf_err(-EINVAL);

	iter_info_len = OPTS_GET(opts, iter_info_len, 0);
	target_btf_id = OPTS_GET(opts, target_btf_id, 0);

	/* validate we don't have unexpected combinations of non-zero fields */
	if (iter_info_len || target_btf_id) {
		if (iter_info_len && target_btf_id)
			return libbpf_err(-EINVAL);
		if (!OPTS_ZEROED(opts, target_btf_id))
			return libbpf_err(-EINVAL);
	}

	memset(&attr, 0, attr_sz);
	attr.link_create.prog_fd = prog_fd;
	attr.link_create.target_fd = target_fd;
	attr.link_create.attach_type = attach_type;
	attr.link_create.flags = OPTS_GET(opts, flags, 0);

	if (target_btf_id) {
		attr.link_create.target_btf_id = target_btf_id;
		goto proceed;
	}

	switch (attach_type) {
	case BPF_TRACE_ITER:
		attr.link_create.iter_info = ptr_to_u64(OPTS_GET(opts, iter_info, (void *)0));
		attr.link_create.iter_info_len = iter_info_len;
		break;
	case BPF_PERF_EVENT:
		attr.link_create.perf_event.bpf_cookie = OPTS_GET(opts, perf_event.bpf_cookie, 0);
		if (!OPTS_ZEROED(opts, perf_event))
			return libbpf_err(-EINVAL);
		break;
	case BPF_TRACE_KPROBE_MULTI:
		attr.link_create.kprobe_multi.flags = OPTS_GET(opts, kprobe_multi.flags, 0);
		attr.link_create.kprobe_multi.cnt = OPTS_GET(opts, kprobe_multi.cnt, 0);
		attr.link_create.kprobe_multi.syms = ptr_to_u64(OPTS_GET(opts, kprobe_multi.syms, 0));
		attr.link_create.kprobe_multi.addrs = ptr_to_u64(OPTS_GET(opts, kprobe_multi.addrs, 0));
		attr.link_create.kprobe_multi.cookies = ptr_to_u64(OPTS_GET(opts, kprobe_multi.cookies, 0));
		if (!OPTS_ZEROED(opts, kprobe_multi))
			return libbpf_err(-EINVAL);
		break;
	case BPF_TRACE_FENTRY:
	case BPF_TRACE_FEXIT:
	case BPF_MODIFY_RETURN:
	case BPF_LSM_MAC:
		attr.link_create.tracing.cookie = OPTS_GET(opts, tracing.cookie, 0);
		if (!OPTS_ZEROED(opts, tracing))
			return libbpf_err(-EINVAL);
		break;
	default:
		if (!OPTS_ZEROED(opts, flags))
			return libbpf_err(-EINVAL);
		break;
	}
proceed:
	fd = sys_bpf_fd(BPF_LINK_CREATE, &attr, attr_sz);
	if (fd >= 0)
		return fd;
	/* we'll get EINVAL if LINK_CREATE doesn't support attaching fentry
	 * and other similar programs
	 */
	err = -errno;
	if (err != -EINVAL)
		return libbpf_err(err);

	/* if user used features not supported by
	 * BPF_RAW_TRACEPOINT_OPEN command, then just give up immediately
	 */
	if (attr.link_create.target_fd || attr.link_create.target_btf_id)
		return libbpf_err(err);
	if (!OPTS_ZEROED(opts, sz))
		return libbpf_err(err);

	/* otherwise, for few select kinds of programs that can be
	 * attached using BPF_RAW_TRACEPOINT_OPEN command, try that as
	 * a fallback for older kernels
	 */
	switch (attach_type) {
	case BPF_TRACE_RAW_TP:
	case BPF_LSM_MAC:
	case BPF_TRACE_FENTRY:
	case BPF_TRACE_FEXIT:
	case BPF_MODIFY_RETURN:
		return bpf_raw_tracepoint_open(NULL, prog_fd);
	default:
		return libbpf_err(err);
	}
}