libbpf: add tracepoint attach API

Allow attaching BPF programs to kernel tracepoint BPF hooks specified by
category and name.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b5b49dd..85174fc 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4190,6 +4190,85 @@ struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,
        return link;
 }
 
+static int determine_tracepoint_id(const char *tp_category,
+                                  const char *tp_name)
+{
+       char file[PATH_MAX];
+       int ret;
+
+       ret = snprintf(file, sizeof(file),
+                      "/sys/kernel/debug/tracing/events/%s/%s/id",
+                      tp_category, tp_name);
+       if (ret < 0)
+               return -errno;
+       if (ret >= sizeof(file)) {
+               pr_debug("tracepoint %s/%s path is too long\n",
+                        tp_category, tp_name);
+               return -E2BIG;
+       }
+       return parse_uint_from_file(file, "%d\n");
+}
+
+static int perf_event_open_tracepoint(const char *tp_category,
+                                     const char *tp_name)
+{
+       struct perf_event_attr attr = {};
+       char errmsg[STRERR_BUFSIZE];
+       int tp_id, pfd, err;
+
+       tp_id = determine_tracepoint_id(tp_category, tp_name);
+       if (tp_id < 0) {
+               pr_warning("failed to determine tracepoint '%s/%s' perf event ID: %s\n",
+                          tp_category, tp_name,
+                          libbpf_strerror_r(tp_id, errmsg, sizeof(errmsg)));
+               return tp_id;
+       }
+
+       attr.type = PERF_TYPE_TRACEPOINT;
+       attr.size = sizeof(attr);
+       attr.config = tp_id;
+
+       pfd = syscall(__NR_perf_event_open, &attr, -1 /* pid */, 0 /* cpu */,
+                     -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
+       if (pfd < 0) {
+               err = -errno;
+               pr_warning("tracepoint '%s/%s' perf_event_open() failed: %s\n",
+                          tp_category, tp_name,
+                          libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+               return err;
+       }
+       return pfd;
+}
+
+struct bpf_link *bpf_program__attach_tracepoint(struct bpf_program *prog,
+                                               const char *tp_category,
+                                               const char *tp_name)
+{
+       char errmsg[STRERR_BUFSIZE];
+       struct bpf_link *link;
+       int pfd, err;
+
+       pfd = perf_event_open_tracepoint(tp_category, tp_name);
+       if (pfd < 0) {
+               pr_warning("program '%s': failed to create tracepoint '%s/%s' perf event: %s\n",
+                          bpf_program__title(prog, false),
+                          tp_category, tp_name,
+                          libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+               return ERR_PTR(pfd);
+       }
+       link = bpf_program__attach_perf_event(prog, pfd);
+       if (IS_ERR(link)) {
+               close(pfd);
+               err = PTR_ERR(link);
+               pr_warning("program '%s': failed to attach to tracepoint '%s/%s': %s\n",
+                          bpf_program__title(prog, false),
+                          tp_category, tp_name,
+                          libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+               return link;
+       }
+       return link;
+}
+
 enum bpf_perf_event_ret
 bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
                           void **copy_mem, size_t *copy_size,

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index bd767cc..60611f4 100644 (file)
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -178,6 +178,10 @@ LIBBPF_API struct bpf_link *
 bpf_program__attach_uprobe(struct bpf_program *prog, bool retprobe,
                           pid_t pid, const char *binary_path,
                           size_t func_offset);
+LIBBPF_API struct bpf_link *
+bpf_program__attach_tracepoint(struct bpf_program *prog,
+                              const char *tp_category,
+                              const char *tp_name);
 
 struct bpf_insn;
 

diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 57a40fb..3c618b7 100644 (file)
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -171,6 +171,7 @@ LIBBPF_0.0.4 {
                bpf_object__load_xattr;
                bpf_program__attach_kprobe;
                bpf_program__attach_perf_event;
+               bpf_program__attach_tracepoint;
                bpf_program__attach_uprobe;
                btf_dump__dump_type;
                btf_dump__free;