[PATCH v2 bpf-next 4/7] libbpf: add tracepoint/raw tracepoint attach API

[Andrii Nakryiko <andriin@xxxxxx>]

Add APIs allowing to attach BPF program to kernel tracepoints. Raw
tracepoint attach API is also added for uniform per-BPF-program API,
but is mostly a wrapper around existing bpf_raw_tracepoint_open call.

Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
---
 tools/lib/bpf/libbpf.c   | 98 ++++++++++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.h   |  5 ++
 tools/lib/bpf/libbpf.map |  2 +
 3 files changed, 105 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d506772df350..9a4199b51300 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4176,6 +4176,104 @@ int bpf_program__attach_uprobe(struct bpf_program *prog, bool retprobe,
 	return pfd;
 }
 
+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);
+}
+
+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 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;
+}
+
+int bpf_program__attach_tracepoint(struct bpf_program *prog,
+				   const char *tp_category,
+				   const char *tp_name)
+{
+	char errmsg[STRERR_BUFSIZE];
+	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 pfd;
+	}
+	err = bpf_program__attach_perf_event(prog, pfd);
+	if (err) {
+		libbpf_perf_event_disable_and_close(pfd);
+		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 err;
+	}
+	return pfd;
+}
+
+int bpf_program__attach_raw_tracepoint(struct bpf_program *prog,
+				       const char *tp_name)
+{
+	char errmsg[STRERR_BUFSIZE];
+	int bpf_fd, pfd;
+
+	bpf_fd = bpf_program__fd(prog);
+	if (bpf_fd < 0) {
+		pr_warning("program '%s': can't attach before loaded\n",
+			   bpf_program__title(prog, false));
+		return -EINVAL;
+	}
+	pfd = bpf_raw_tracepoint_open(tp_name, bpf_fd);
+	if (pfd < 0) {
+		pr_warning("program '%s': failed to attach to raw tracepoint '%s': %s\n",
+			   bpf_program__title(prog, false), tp_name,
+			   libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+		return pfd;
+	}
+	return pfd;
+}
+
 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 a7264f06aa5f..bf7020a565c6 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -176,6 +176,11 @@ LIBBPF_API int bpf_program__attach_uprobe(struct bpf_program *prog,
 					  pid_t pid,
 					  const char *binary_path,
 					  size_t func_offset);
+LIBBPF_API int bpf_program__attach_tracepoint(struct bpf_program *prog,
+					      const char *tp_category,
+					      const char *tp_name);
+LIBBPF_API int bpf_program__attach_raw_tracepoint(struct bpf_program *prog,
+						  const char *tp_name);
 
 struct bpf_insn;
 
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 1a982c2e1751..2382fbda4cbb 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -174,6 +174,8 @@ LIBBPF_0.0.4 {
 		bpf_object__load_xattr;
 		bpf_program__attach_kprobe;
 		bpf_program__attach_perf_event;
+		bpf_program__attach_raw_tracepoint;
+		bpf_program__attach_tracepoint;
 		bpf_program__attach_uprobe;
 		libbpf_num_possible_cpus;
 		libbpf_perf_event_disable_and_close;
-- 
2.17.1