Allow obtaining BPFPerfBuffer pointer for polling

examples/cpp/FollyRequestContextSwitch.cc

@@ -98,8 +98,11 @@ int main(int argc, char** argv) {
 
  signal(SIGINT, signal_handler);
  std::cout << "Started tracing, hit Ctrl-C to terminate." << std::endl;
- while (true)
- bpf->poll_perf_buffer("events");
+ auto perf_buffer = bpf->get_perf_buffer("events");
+ if (perf_buffer)
+ while (true)
+ // 100ms timeout
+ perf_buffer->poll(100);
 
  return 0;
 }

src/cc/api/BPF.cc

@@ -443,6 +443,11 @@ StatusTuple BPF::close_perf_buffer(const std::string& name) {
  return StatusTuple(0);
 }
 
+BPFPerfBuffer* BPF::get_perf_buffer(const std::string& name) {
+ auto it = perf_buffers_.find(name);
+ return (it == perf_buffers_.end()) ? nullptr : it->second;
+}
+
 void BPF::poll_perf_buffer(const std::string& name, int timeout_ms) {
  auto it = perf_buffers_.find(name);
  if (it == perf_buffers_.end())

src/cc/api/BPF.h

@@ -136,11 +136,20 @@ class BPF {
 
  StatusTuple close_perf_event(const std::string& name);
 
+ // Open a Perf Buffer of given name, providing callback and callback cookie
+ // to use when polling. BPF class owns the opened Perf Buffer and will free
+ // it on-demand or on destruction.
  StatusTuple open_perf_buffer(const std::string& name, perf_reader_raw_cb cb,
  perf_reader_lost_cb lost_cb = nullptr,
  void* cb_cookie = nullptr,
  int page_cnt = DEFAULT_PERF_BUFFER_PAGE_CNT);
+ // Close and free the Perf Buffer of given name.
  StatusTuple close_perf_buffer(const std::string& name);
+ // Obtain an pointer to the opened BPFPerfBuffer instance of given name.
+ // Will return nullptr if such open Perf Buffer doesn't exist.
+ BPFPerfBuffer* get_perf_buffer(const std::string& name);
+ // Poll an opened Perf Buffer of given name with given timeout, using callback
+ // provided when opening. Do nothing if such open Perf Buffer doesn't exist.
  void poll_perf_buffer(const std::string& name, int timeout_ms = -1);
 
  StatusTuple load_func(const std::string& func_name, enum bpf_prog_type type,