libbpf: Introduce libbpf_attach_type_by_name

There is a common use-case when ELF object contains multiple BPF
programs and every program has its own section name. If it's cgroup-bpf
then programs have to be 1) loaded and 2) attached to a cgroup.

It's convenient to have information necessary to load BPF program
together with program itself. This is where section name works fine in
conjunction with libbpf_prog_type_by_name that identifies prog_type and
expected_attach_type and these can be used with BPF_PROG_LOAD.

But there is currently no way to identify attach_type by section name
and it leads to messy code in user space that reinvents guessing logic
every time it has to identify attach type to use with BPF_PROG_ATTACH.

The patch introduces libbpf_attach_type_by_name that guesses attach type
by section name if a program can be attached.

The difference between expected_attach_type provided by
libbpf_prog_type_by_name and attach_type provided by
libbpf_attach_type_by_name is the former is used at BPF_PROG_LOAD time
and can be zero if a program of prog_type X has only one corresponding
attach type Y whether the latter provides specific attach type to use
with BPF_PROG_ATTACH.

No new section names were added to section_names array. Only existing
ones were reorganized and attach_type was added where appropriate.
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/libbpf.c

@@ -2085,22 +2085,31 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
 	prog->expected_attach_type = type;
 }
 
-#define BPF_PROG_SEC_FULL(string, ptype, atype) \
-	{ string, sizeof(string) - 1, ptype, atype }
+#define BPF_PROG_SEC_IMPL(string, ptype, eatype, atype) \
+	{ string, sizeof(string) - 1, ptype, eatype, atype }
 
-#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_FULL(string, ptype, 0)
+/* Programs that can NOT be attached. */
+#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, -EINVAL)
 
-#define BPF_S_PROG_SEC(string, ptype) \
-	BPF_PROG_SEC_FULL(string, BPF_PROG_TYPE_CGROUP_SOCK, ptype)
+/* Programs that can be attached. */
+#define BPF_APROG_SEC(string, ptype, atype) \
+	BPF_PROG_SEC_IMPL(string, ptype, 0, atype)
 
-#define BPF_SA_PROG_SEC(string, ptype) \
-	BPF_PROG_SEC_FULL(string, BPF_PROG_TYPE_CGROUP_SOCK_ADDR, ptype)
+/* Programs that must specify expected attach type at load time. */
+#define BPF_EAPROG_SEC(string, ptype, eatype) \
+	BPF_PROG_SEC_IMPL(string, ptype, eatype, eatype)
+
+/* Programs that can be attached but attach type can't be identified by section
+ * name. Kept for backward compatibility.
+ */
+#define BPF_APROG_COMPAT(string, ptype) BPF_PROG_SEC(string, ptype)
 
 static const struct {
 	const char *sec;
 	size_t len;
 	enum bpf_prog_type prog_type;
 	enum bpf_attach_type expected_attach_type;
+	enum bpf_attach_type attach_type;
 } section_names[] = {
 	BPF_PROG_SEC("socket",			BPF_PROG_TYPE_SOCKET_FILTER),
 	BPF_PROG_SEC("kprobe/",			BPF_PROG_TYPE_KPROBE),
@@ -2111,32 +2120,47 @@ static const struct {
 	BPF_PROG_SEC("raw_tracepoint/",		BPF_PROG_TYPE_RAW_TRACEPOINT),
 	BPF_PROG_SEC("xdp",			BPF_PROG_TYPE_XDP),
 	BPF_PROG_SEC("perf_event",		BPF_PROG_TYPE_PERF_EVENT),
-	BPF_PROG_SEC("cgroup/skb",	BPF_PROG_TYPE_CGROUP_SKB),
-	BPF_PROG_SEC("cgroup/sock",	BPF_PROG_TYPE_CGROUP_SOCK),
-	BPF_PROG_SEC("cgroup/dev",	BPF_PROG_TYPE_CGROUP_DEVICE),
 	BPF_PROG_SEC("lwt_in",			BPF_PROG_TYPE_LWT_IN),
 	BPF_PROG_SEC("lwt_out",			BPF_PROG_TYPE_LWT_OUT),
 	BPF_PROG_SEC("lwt_xmit",		BPF_PROG_TYPE_LWT_XMIT),
 	BPF_PROG_SEC("lwt_seg6local",		BPF_PROG_TYPE_LWT_SEG6LOCAL),
-	BPF_PROG_SEC("sockops",		BPF_PROG_TYPE_SOCK_OPS),
-	BPF_PROG_SEC("sk_skb",		BPF_PROG_TYPE_SK_SKB),
-	BPF_PROG_SEC("sk_msg",		BPF_PROG_TYPE_SK_MSG),
-	BPF_PROG_SEC("lirc_mode2",	BPF_PROG_TYPE_LIRC_MODE2),
-	BPF_PROG_SEC("flow_dissector",	BPF_PROG_TYPE_FLOW_DISSECTOR),
-	BPF_SA_PROG_SEC("cgroup/bind4",	BPF_CGROUP_INET4_BIND),
-	BPF_SA_PROG_SEC("cgroup/bind6",	BPF_CGROUP_INET6_BIND),
-	BPF_SA_PROG_SEC("cgroup/connect4", BPF_CGROUP_INET4_CONNECT),
-	BPF_SA_PROG_SEC("cgroup/connect6", BPF_CGROUP_INET6_CONNECT),
-	BPF_SA_PROG_SEC("cgroup/sendmsg4", BPF_CGROUP_UDP4_SENDMSG),
-	BPF_SA_PROG_SEC("cgroup/sendmsg6", BPF_CGROUP_UDP6_SENDMSG),
-	BPF_S_PROG_SEC("cgroup/post_bind4", BPF_CGROUP_INET4_POST_BIND),
-	BPF_S_PROG_SEC("cgroup/post_bind6", BPF_CGROUP_INET6_POST_BIND),
+	BPF_APROG_COMPAT("cgroup/skb",		BPF_PROG_TYPE_CGROUP_SKB),
+	BPF_APROG_SEC("cgroup/sock",		BPF_PROG_TYPE_CGROUP_SOCK,
+						BPF_CGROUP_INET_SOCK_CREATE),
+	BPF_EAPROG_SEC("cgroup/post_bind4",	BPF_PROG_TYPE_CGROUP_SOCK,
+						BPF_CGROUP_INET4_POST_BIND),
+	BPF_EAPROG_SEC("cgroup/post_bind6",	BPF_PROG_TYPE_CGROUP_SOCK,
+						BPF_CGROUP_INET6_POST_BIND),
+	BPF_APROG_SEC("cgroup/dev",		BPF_PROG_TYPE_CGROUP_DEVICE,
+						BPF_CGROUP_DEVICE),
+	BPF_APROG_SEC("sockops",		BPF_PROG_TYPE_SOCK_OPS,
+						BPF_CGROUP_SOCK_OPS),
+	BPF_APROG_COMPAT("sk_skb",		BPF_PROG_TYPE_SK_SKB),
+	BPF_APROG_SEC("sk_msg",			BPF_PROG_TYPE_SK_MSG,
+						BPF_SK_MSG_VERDICT),
+	BPF_APROG_SEC("lirc_mode2",		BPF_PROG_TYPE_LIRC_MODE2,
+						BPF_LIRC_MODE2),
+	BPF_APROG_SEC("flow_dissector",		BPF_PROG_TYPE_FLOW_DISSECTOR,
+						BPF_FLOW_DISSECTOR),
+	BPF_EAPROG_SEC("cgroup/bind4",		BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
+						BPF_CGROUP_INET4_BIND),
+	BPF_EAPROG_SEC("cgroup/bind6",		BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
+						BPF_CGROUP_INET6_BIND),
+	BPF_EAPROG_SEC("cgroup/connect4",	BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
+						BPF_CGROUP_INET4_CONNECT),
+	BPF_EAPROG_SEC("cgroup/connect6",	BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
+						BPF_CGROUP_INET6_CONNECT),
+	BPF_EAPROG_SEC("cgroup/sendmsg4",	BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
+						BPF_CGROUP_UDP4_SENDMSG),
+	BPF_EAPROG_SEC("cgroup/sendmsg6",	BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
+						BPF_CGROUP_UDP6_SENDMSG),
 };
 
+#undef BPF_PROG_SEC_IMPL
 #undef BPF_PROG_SEC
-#undef BPF_PROG_SEC_FULL
-#undef BPF_S_PROG_SEC
-#undef BPF_SA_PROG_SEC
+#undef BPF_APROG_SEC
+#undef BPF_EAPROG_SEC
+#undef BPF_APROG_COMPAT
 
 int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
 			     enum bpf_attach_type *expected_attach_type)
@@ -2156,6 +2180,25 @@ int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
 	return -EINVAL;
 }
 
+int libbpf_attach_type_by_name(const char *name,
+			       enum bpf_attach_type *attach_type)
+{
+	int i;
+
+	if (!name)
+		return -EINVAL;
+
+	for (i = 0; i < ARRAY_SIZE(section_names); i++) {
+		if (strncmp(name, section_names[i].sec, section_names[i].len))
+			continue;
+		if (section_names[i].attach_type == -EINVAL)
+			return -EINVAL;
+		*attach_type = section_names[i].attach_type;
+		return 0;
+	}
+	return -EINVAL;
+}
+
 static int
 bpf_program__identify_section(struct bpf_program *prog,
 			      enum bpf_prog_type *prog_type,

tools/lib/bpf/libbpf.h

@@ -104,6 +104,8 @@ void *bpf_object__priv(struct bpf_object *prog);
 
 int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
 			     enum bpf_attach_type *expected_attach_type);
+int libbpf_attach_type_by_name(const char *name,
+			       enum bpf_attach_type *attach_type);
 
 /* Accessors of bpf_program */
 struct bpf_program;