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>

2 files changed, 84 insertions, 39 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 4f8d43ae20d2..59e589a64d5c 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2085,58 +2085,82 @@ 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),
-        BPF_PROG_SEC("kretprobe/",      BPF_PROG_TYPE_KPROBE),
-        BPF_PROG_SEC("classifier",      BPF_PROG_TYPE_SCHED_CLS),
-        BPF_PROG_SEC("action",          BPF_PROG_TYPE_SCHED_ACT),
-        BPF_PROG_SEC("tracepoint/",     BPF_PROG_TYPE_TRACEPOINT),
-        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_PROG_SEC("socket",                  BPF_PROG_TYPE_SOCKET_FILTER),
+        BPF_PROG_SEC("kprobe/",                 BPF_PROG_TYPE_KPROBE),
+        BPF_PROG_SEC("kretprobe/",              BPF_PROG_TYPE_KPROBE),
+        BPF_PROG_SEC("classifier",              BPF_PROG_TYPE_SCHED_CLS),
+        BPF_PROG_SEC("action",                  BPF_PROG_TYPE_SCHED_ACT),
+        BPF_PROG_SEC("tracepoint/",             BPF_PROG_TYPE_TRACEPOINT),
+        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("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_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,
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index e3b00e23e181..511c1294dcbf 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/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;