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

Andrii Nakryiko
2019-06-21T04:56:14Z

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@fb.com>
---
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