From b36c8f2fc5b970abaea95ebd23de93c6e0aeae05 Mon Sep 17 00:00:00 2001
From: Bartosz Taudul <wolf@nereid.pl>
Date: Sun, 30 Aug 2026 16:46:42 +0200
Subject: [PATCH] Refuse to start without tracefs.

The client's system tracing cannot start without a tracefs (or debugfs)
mount - the tracepoint ids live under it - so starting anyway would
capture no samples.
---
 monitor/src/monitor.cpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/monitor/src/monitor.cpp b/monitor/src/monitor.cpp
index 168a2bc0..e72cae9b 100644
--- a/monitor/src/monitor.cpp
+++ b/monitor/src/monitor.cpp
@@ -482,6 +482,12 @@ static int RunAttached( pid_t pid )
     int hwErrno = 0;
     if( !PreflightSamplingEvent( pid, kernelFrames, hwStats, hwErrno ) ) return 1;
 
+    if( !GetTraceFsPath() )
+    {
+        fprintf( stderr, "No tracefs mount found: the client's system tracing cannot start without it, so no samples would be captured.\n" );
+        return 1;
+    }
+
     tracy::StartupProfiler();
     if( tracy::IsSystemTracingFailed() )
     {
@@ -608,6 +614,14 @@ static int RunForked( int argc, char** argv )
         return 1;
     }
 
+    if( !GetTraceFsPath() )
+    {
+        fprintf( stderr, "No tracefs mount found: the client's system tracing cannot start without it, so no samples would be captured.\n" );
+        kill( childPid, SIGKILL );
+        waitpid( childPid, nullptr, 0 );
+        return 1;
+    }
+
     tracy::StartupProfiler();
     if( tracy::IsSystemTracingFailed() )
     {