Merge pull request iovisor#1620 from palmtenor/perf_buffer_ptr

C++ API: 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

@@ -443,11 +443,16 @@ StatusTuple BPF::close_perf_buffer(const std::string& name) {
  return StatusTuple(0);
 }
 
-void BPF::poll_perf_buffer(const std::string& name, int timeout) {
+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())
  return;
- it->second->poll(timeout);
+ it->second->poll(timeout_ms);
 }
 
 StatusTuple BPF::load_func(const std::string& func_name, bpf_prog_type type,

src/cc/api/BPF.h

@@ -136,12 +136,21 @@ 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);
- void poll_perf_buffer(const std::string& name, int timeout = -1);
+ // 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,
  int& fd);

src/cc/api/BPFTable.cc

@@ -295,10 +295,10 @@ StatusTuple BPFPerfBuffer::close_all_cpu() {
  return StatusTuple(0);
 }
 
-void BPFPerfBuffer::poll(int timeout) {
+void BPFPerfBuffer::poll(int timeout_ms) {
  if (epfd_ < 0)
  return;
- int cnt = epoll_wait(epfd_, ep_events_.get(), cpu_readers_.size(), timeout);
+ int cnt = epoll_wait(epfd_, ep_events_.get(), cpu_readers_.size(), timeout_ms);
  if (cnt <= 0)
  return;
  for (int i = 0; i < cnt; i++)

src/cc/api/BPFTable.h

@@ -309,7 +309,7 @@ class BPFPerfBuffer : public BPFTableBase<int, int> {
  StatusTuple open_all_cpu(perf_reader_raw_cb cb, perf_reader_lost_cb lost_cb,
  void* cb_cookie, int page_cnt);
  StatusTuple close_all_cpu();
- void poll(int timeout);
+ void poll(int timeout_ms);
 
  private:
  StatusTuple open_on_cpu(perf_reader_raw_cb cb, perf_reader_lost_cb lost_cb,