make loop/chunk limit variables gflags

Signed-off-by: Benjamin Kilimnik <[email protected]>

src/stirling/source_connectors/socket_tracer/socket_trace_connector.cc

@@ -176,6 +176,15 @@ DEFINE_bool(
     stirling_debug_tls_sources, gflags::BoolFromEnv("PX_DEBUG_TLS_SOURCES", false),
     "If true, stirling will add additional prometheus metrics regarding the traced tls sources");
 
+DEFINE_uint32(stirling_bpf_loop_limit, 42,
+              "The maximum number of iovecs to capture for syscalls. "
+              "Set conservatively for older kernels by default to keep the instruction count below "
+              "BPF's limit for version 4 kernels (4096 per probe).");
+
+DEFINE_uint32(stirling_bpf_chunk_limit, 4,
+              "The maximum number of chunks a perf_submit can support. "
+              "This applies to messages that are over MAX_MSG_SIZE.");
+
 OBJ_STRVIEW(socket_trace_bcc_script, socket_trace);
 
 namespace px {
@@ -434,17 +443,15 @@ auto SocketTraceConnector::InitPerfBufferSpecs() {
 Status SocketTraceConnector::InitBPF() {
   // set BPF loop limit and chunk limit based on kernel version
   auto kernel = system::GetCachedKernelVersion();
-  int loop_limit = 42;
-  int chunk_limit = 4;
   if (kernel.version >= 5 || (kernel.version == 5 && kernel.major_rev >= 1)) {
     // Kernels >= 5.1 have higher BPF instruction limits (1 million for verifier).
     // This enables a 21x increase to our loop and chunk limits
-    loop_limit = 882;
-    chunk_limit = 84;
+    FLAGS_stirling_bpf_loop_limit = 882;
+    FLAGS_stirling_bpf_chunk_limit = 84;
     LOG(INFO) << absl::Substitute(
         "Kernel version greater than V5.1 detected ($0), raised loop limit to $1 and chunk limit "
         "to $2",
-        kernel.ToString(), loop_limit, chunk_limit);
+        kernel.ToString(), FLAGS_stirling_bpf_loop_limit, FLAGS_stirling_bpf_chunk_limit);
   }
   // PROTOCOL_LIST: Requires update on new protocols.
   std::vector<std::string> defines = {
@@ -460,8 +467,8 @@ Status SocketTraceConnector::InitBPF() {
       absl::StrCat("-DENABLE_NATS_TRACING=", protocol_transfer_specs_[kProtocolNATS].enabled),
       absl::StrCat("-DENABLE_AMQP_TRACING=", protocol_transfer_specs_[kProtocolAMQP].enabled),
       absl::StrCat("-DENABLE_MONGO_TRACING=", protocol_transfer_specs_[kProtocolMongo].enabled),
-      absl::StrCat("-DBPF_LOOP_LIMIT=", loop_limit),
-      absl::StrCat("-DBPF_CHUNK_LIMIT=", chunk_limit),
+      absl::StrCat("-DBPF_LOOP_LIMIT=", FLAGS_stirling_bpf_loop_limit),
+      absl::StrCat("-DBPF_CHUNK_LIMIT=", FLAGS_stirling_bpf_chunk_limit),
   };
   PX_RETURN_IF_ERROR(bcc_->InitBPFProgram(socket_trace_bcc_script, defines));