libbpf: Assign cookies to links in libbpf.

Add a cookie field to the attributes of bpf_link_create().
Add bpf_program__attach_trace_opts() to attach a cookie to a link.

Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>

Author: Kui-Feng Lee

tools/lib/bpf/bpf.c

@@ -863,6 +863,13 @@ int bpf_link_create(int prog_fd, int target_fd,
 		if (!OPTS_ZEROED(opts, kprobe_multi))
 			return libbpf_err(-EINVAL);
 		break;
+	case BPF_TRACE_FENTRY:
+	case BPF_TRACE_FEXIT:
+	case BPF_MODIFY_RETURN:
+		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);

tools/lib/bpf/bpf.h

@@ -410,6 +410,9 @@ struct bpf_link_create_opts {
 	__u32 iter_info_len;
 	__u32 target_btf_id;
 	union {
+		struct {
+			__u64 cookie;
+		} tracing;
 		struct {
 			__u64 bpf_cookie;
 		} perf_event;

tools/lib/bpf/libbpf.c

@@ -11262,6 +11262,44 @@ struct bpf_link *bpf_program__attach_trace(const struct bpf_program *prog)
 	return bpf_program__attach_btf_id(prog);
 }
 
+struct bpf_link *bpf_program__attach_trace_opts(const struct bpf_program *prog,
+						const struct bpf_trace_opts *opts)
+{
+	char errmsg[STRERR_BUFSIZE];
+	struct bpf_link *link;
+	int prog_fd, pfd;
+	LIBBPF_OPTS(bpf_link_create_opts, link_opts);
+
+	/* Fallback for cookie is 0.  Old kernels don't create
+	 * fentry/fexit links through LINK_CREATE.
+	 */
+	if (OPTS_GET(opts, cookie, 0))
+		return bpf_program__attach_trace(prog);
+
+	prog_fd = bpf_program__fd(prog);
+	if (prog_fd < 0) {
+		pr_warn("prog '%s': can't attach before loaded\n", prog->name);
+		return libbpf_err_ptr(-EINVAL);
+	}
+
+	link = calloc(1, sizeof(*link));
+	if (!link)
+		return libbpf_err_ptr(-ENOMEM);
+	link->detach = &bpf_link__detach_fd;
+
+	link_opts.tracing.cookie = OPTS_GET(opts, cookie, 0);
+	pfd = bpf_link_create(prog_fd, 0, prog->expected_attach_type, &link_opts);
+	if (pfd < 0) {
+		pfd = -errno;
+		free(link);
+		pr_warn("prog '%s': failed to attach: %s\n",
+			prog->name, libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+		return libbpf_err_ptr(pfd);
+	}
+	link->fd = pfd;
+	return (struct bpf_link *)link;
+}
+
 struct bpf_link *bpf_program__attach_lsm(const struct bpf_program *prog)
 {
 	return bpf_program__attach_btf_id(prog);

tools/lib/bpf/libbpf.h

@@ -563,8 +563,20 @@ bpf_program__attach_tracepoint_opts(const struct bpf_program *prog,
 LIBBPF_API struct bpf_link *
 bpf_program__attach_raw_tracepoint(const struct bpf_program *prog,
 				   const char *tp_name);
+
+struct bpf_trace_opts {
+	/* size of this struct, for forward/backward compatibility */
+	size_t sz;
+	/* custom user-provided value fetchable through bpf_get_attach_cookie() */
+	__u64 cookie;
+};
+#define bpf_trace_opts__last_field cookie
+
 LIBBPF_API struct bpf_link *
 bpf_program__attach_trace(const struct bpf_program *prog);
+LIBBPF_API struct bpf_link *
+bpf_program__attach_trace_opts(const struct bpf_program *prog, const struct bpf_trace_opts *opts);
+
 LIBBPF_API struct bpf_link *
 bpf_program__attach_lsm(const struct bpf_program *prog);
 LIBBPF_API struct bpf_link *

tools/lib/bpf/libbpf.map

@@ -444,6 +444,7 @@ LIBBPF_0.8.0 {
 	global:
 		bpf_object__destroy_subskeleton;
 		bpf_object__open_subskeleton;
+		bpf_program__attach_trace_opts;
 		bpf_program__attach_usdt;
 		libbpf_register_prog_handler;
 		libbpf_unregister_prog_handler;