Fix TCPSendStack example stack id error handling

examples/cpp/TCPSendStack.cc

@@ -27,17 +27,15 @@ struct stack_key_t {
  int kernel_stack;
 };
 
-BPF_STACK_TRACE(stack_traces, 10240);
+BPF_STACK_TRACE(stack_traces, 16384);
 BPF_HASH(counts, struct stack_key_t, uint64_t);
 
 int on_tcp_send(struct pt_regs *ctx) {
  struct stack_key_t key = {};
  key.pid = bpf_get_current_pid_tgid() >> 32;
  bpf_get_current_comm(&key.name, sizeof(key.name));
- key.kernel_stack = stack_traces.get_stackid(ctx, BPF_F_REUSE_STACKID);
- key.user_stack = stack_traces.get_stackid(
- ctx, BPF_F_REUSE_STACKID | BPF_F_USER_STACK
- );
+ key.kernel_stack = stack_traces.get_stackid(ctx, 0);
+ key.user_stack = stack_traces.get_stackid(ctx, BPF_F_USER_STACK);
 
  u64 zero = 0, *val;
  val = counts.lookup_or_init(&key, &zero);
@@ -76,6 +74,12 @@ int main(int argc, char** argv) {
  std::cout << "Probing for " << probe_time << " seconds" << std::endl;
  sleep(probe_time);
 
+ auto detach_res = bpf.detach_kprobe("tcp_sendmsg");
+ if (detach_res.code() != 0) {
+ std::cerr << detach_res.msg() << std::endl;
+ return 1;
+ }
+
  auto table =
  bpf.get_hash_table<stack_key_t, uint64_t>("counts").get_table_offline();
  std::sort(
@@ -84,31 +88,42 @@ int main(int argc, char** argv) {
  std::pair<stack_key_t, uint64_t> b) { return a.second < b.second; });
  auto stacks = bpf.get_stack_table("stack_traces");
 
+ int lost_stacks = 0;
  for (auto it : table) {
  std::cout << "PID: " << it.first.pid << " (" << it.first.name << ") "
  << "made " << it.second
  << " TCP sends on following stack: " << std::endl;
- std::cout << " Kernel Stack:" << std::endl;
  if (it.first.kernel_stack >= 0) {
+ std::cout << " Kernel Stack:" << std::endl;
  auto syms = stacks.get_stack_symbol(it.first.kernel_stack, -1);
  for (auto sym : syms)
  std::cout << " " << sym << std::endl;
- } else
- std::cout << " " << it.first.kernel_stack << std::endl;
- std::cout << " User Stack:" << std::endl;
+ } else {
+ // -EFAULT normally means the stack is not availiable and not an error
+ if (it.first.kernel_stack != -EFAULT) {
+ lost_stacks++;
+ std::cout << " [Lost Kernel Stack" << it.first.kernel_stack << "]"
+ << std::endl;
+ }
+ }
  if (it.first.user_stack >= 0) {
+ std::cout << " User Stack:" << std::endl;
  auto syms = stacks.get_stack_symbol(it.first.user_stack, it.first.pid);
  for (auto sym : syms)
  std::cout << " " << sym << std::endl;
- } else
- std::cout << " " << it.first.user_stack << std::endl;
+ } else {
+ // -EFAULT normally means the stack is not availiable and not an error
+ if (it.first.user_stack != -EFAULT) {
+ lost_stacks++;
+ std::cout << " [Lost User Stack " << it.first.user_stack << "]"
+ << std::endl;
+ }
+ }
  }
 
- auto detach_res = bpf.detach_kprobe("tcp_sendmsg");
- if (detach_res.code() != 0) {
- std::cerr << detach_res.msg() << std::endl;
- return 1;
- }
+ if (lost_stacks > 0)
+ std::cout << "Total " << lost_stacks << " stack-traces lost due to "
+ << "hash collision or stack table full" << std::endl;
 
  return 0;
 }