trace_events: add file pattern cli option

Allow the user to specify the filepath for the trace_events log file
using a template string.

PR-URL: https://github.com/nodejs/node/pull/18480
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

5 files changed, 44 insertions, 10 deletions

diff --git a/src/node.cc b/src/node.cc
index d3749b9cc1..64de859bc6 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -192,6 +192,8 @@ static node_module* modlist_linked;
 static node_module* modlist_addon;
 static bool trace_enabled = false;
 static std::string trace_enabled_categories;  // NOLINT(runtime/string)
+static std::string trace_file_pattern =  // NOLINT(runtime/string)
+  "node_trace.${rotation}.log";
 static bool abort_on_uncaught_exception = false;
 
 // Bit flag used to track security reverts (see node_revert.h)
@@ -275,7 +277,7 @@ static struct {
 #if NODE_USE_V8_PLATFORM
   void Initialize(int thread_pool_size) {
     if (trace_enabled) {
-      tracing_agent_.reset(new tracing::Agent());
+      tracing_agent_.reset(new tracing::Agent(trace_file_pattern));
       platform_ = new NodePlatform(thread_pool_size,
         tracing_agent_->GetTracingController());
       V8::InitializePlatform(platform_);
@@ -3422,6 +3424,10 @@ static void PrintHelp() {
          "  --trace-events-enabled     track trace events\n"
          "  --trace-event-categories   comma separated list of trace event\n"
          "                             categories to record\n"
+         "  --trace-event-file-pattern Template string specifying the\n"
+         "                             filepath for the trace-events data, it\n"
+         "                             supports ${rotation} and ${pid}\n"
+         "                             log-rotation id. %%2$u is the pid.\n"
          "  --track-heap-objects       track heap object allocations for heap "
          "snapshots\n"
          "  --prof-process             process v8 profiler output generated\n"
@@ -3550,6 +3556,7 @@ static void CheckIfAllowedInEnv(const char* exe, bool is_env,
     "--no-force-async-hooks-checks",
     "--trace-events-enabled",
     "--trace-event-categories",
+    "--trace-event-file-pattern",
     "--track-heap-objects",
     "--zero-fill-buffers",
     "--v8-pool-size",
@@ -3701,6 +3708,14 @@ static void ParseArgs(int* argc,
       }
       args_consumed += 1;
       trace_enabled_categories = categories;
+    } else if (strcmp(arg, "--trace-event-file-pattern") == 0) {
+      const char* file_pattern = argv[index + 1];
+      if (file_pattern == nullptr) {
+        fprintf(stderr, "%s: %s requires an argument\n", argv[0], arg);
+        exit(9);
+      }
+      args_consumed += 1;
+      trace_file_pattern = file_pattern;
     } else if (strcmp(arg, "--track-heap-objects") == 0) {
       track_heap_objects = true;
     } else if (strcmp(arg, "--throw-deprecation") == 0) {
diff --git a/src/tracing/agent.cc b/src/tracing/agent.cc
index 4514a0fce1..71e53e787a 100644
--- a/src/tracing/agent.cc
+++ b/src/tracing/agent.cc
@@ -13,11 +13,12 @@ namespace tracing {
 using v8::platform::tracing::TraceConfig;
 using std::string;
 
-Agent::Agent() {
+Agent::Agent(const std::string& log_file_pattern) {
   int err = uv_loop_init(&tracing_loop_);
   CHECK_EQ(err, 0);
 
-  NodeTraceWriter* trace_writer = new NodeTraceWriter(&tracing_loop_);
+  NodeTraceWriter* trace_writer = new NodeTraceWriter(
+      log_file_pattern, &tracing_loop_);
   TraceBuffer* trace_buffer = new NodeTraceBuffer(
       NodeTraceBuffer::kBufferChunks, trace_writer, &tracing_loop_);
   tracing_controller_ = new TracingController();
diff --git a/src/tracing/agent.h b/src/tracing/agent.h
index 203f53be7e..9d6bc4e90a 100644
--- a/src/tracing/agent.h
+++ b/src/tracing/agent.h
@@ -19,7 +19,7 @@ class TracingController : public v8::platform::tracing::TracingController {
 
 class Agent {
  public:
-  Agent();
+  explicit Agent(const std::string& log_file_pattern);
   void Start(const std::string& enabled_categories);
   void Stop();
 
diff --git a/src/tracing/node_trace_writer.cc b/src/tracing/node_trace_writer.cc
index 9293e9cb8f..15c59fc98a 100644
--- a/src/tracing/node_trace_writer.cc
+++ b/src/tracing/node_trace_writer.cc
@@ -8,8 +8,9 @@
 namespace node {
 namespace tracing {
 
-NodeTraceWriter::NodeTraceWriter(uv_loop_t* tracing_loop)
-    : tracing_loop_(tracing_loop) {
+NodeTraceWriter::NodeTraceWriter(const std::string& log_file_pattern,
+                                 uv_loop_t* tracing_loop)
+    : tracing_loop_(tracing_loop), log_file_pattern_(log_file_pattern) {
   flush_signal_.data = this;
   int err = uv_async_init(tracing_loop_, &flush_signal_, FlushSignalCb);
   CHECK_EQ(err, 0);
@@ -54,12 +55,27 @@ NodeTraceWriter::~NodeTraceWriter() {
   }
 }
 
+void replace_substring(std::string* target,
+                       const std::string& search,
+                       const std::string& insert) {
+  size_t pos = target->find(search);
+  for (; pos != std::string::npos; pos = target->find(search, pos)) {
+    target->replace(pos, search.size(), insert);
+    pos += insert.size();
+  }
+}
+
 void NodeTraceWriter::OpenNewFileForStreaming() {
   ++file_num_;
   uv_fs_t req;
-  std::ostringstream log_file;
-  log_file << "node_trace." << file_num_ << ".log";
-  fd_ = uv_fs_open(tracing_loop_, &req, log_file.str().c_str(),
+
+  // Evaluate a JS-style template string, it accepts the values ${pid} and
+  // ${rotation}
+  std::string filepath(log_file_pattern_);
+  replace_substring(&filepath, "${pid}", std::to_string(uv_os_getpid()));
+  replace_substring(&filepath, "${rotation}", std::to_string(file_num_));
+
+  fd_ = uv_fs_open(tracing_loop_, &req, filepath.c_str(),
       O_CREAT | O_WRONLY | O_TRUNC, 0644, nullptr);
   CHECK_NE(fd_, -1);
   uv_fs_req_cleanup(&req);
diff --git a/src/tracing/node_trace_writer.h b/src/tracing/node_trace_writer.h
index 5abb3e2a61..9211790777 100644
--- a/src/tracing/node_trace_writer.h
+++ b/src/tracing/node_trace_writer.h
@@ -16,7 +16,8 @@ using v8::platform::tracing::TraceWriter;
 
 class NodeTraceWriter : public TraceWriter {
  public:
-  explicit NodeTraceWriter(uv_loop_t* tracing_loop);
+  explicit NodeTraceWriter(const std::string& log_file_pattern,
+                           uv_loop_t* tracing_loop);
   ~NodeTraceWriter();
 
   void AppendTraceEvent(TraceObject* trace_event) override;
@@ -62,6 +63,7 @@ class NodeTraceWriter : public TraceWriter {
   int highest_request_id_completed_ = 0;
   int total_traces_ = 0;
   int file_num_ = 0;
+  const std::string& log_file_pattern_;
   std::ostringstream stream_;
   TraceWriter* json_trace_writer_ = nullptr;
   bool exited_ = false;