FEXServer: Add support for FEX Logging control

Always enables FEXServer log thread when built for Steam so that clients
can be controlled with `STEAM_FEX_LOG=1`. FEX logs will then always go
to FEXServer and those can get directed to wherever pressure-vessel
chooses.

Source/Steam/CompatTool.cpp

@@ -83,6 +83,7 @@ fextl::string GenerateSteamAppConfig(const FEX::Config::PortableInformation& Por
     bool Multiblock = true;
     bool Thunks_GL = false;
     bool Thunks_Vulkan = false;
+    bool EnableLogging = false;
   };
   SteamOptions Options {};
 
@@ -97,6 +98,11 @@ fextl::string GenerateSteamAppConfig(const FEX::Config::PortableInformation& Por
     Options.Multiblock = std::strtoull(steam_fex_multiblock, nullptr, 0) != 0;
   }
 
+  const auto steam_fex_logging = getenv("STEAM_FEX_LOG");
+  if (steam_fex_logging) {
+    Options.EnableLogging = std::strtoull(steam_fex_logging, nullptr, 0) != 0;
+  }
+
   // UI overrides.
   const auto steam_fex_compat = getenv("STEAM_COMPAT_FEX_CONFIG");
   if (steam_fex_compat) {
@@ -123,6 +129,10 @@ fextl::string GenerateSteamAppConfig(const FEX::Config::PortableInformation& Por
     Dest = json_objOpen(Dest, "Config");
     Dest = json_str(Dest, "TSOEnabled", Options.TSO ? "1" : "0");
     Dest = json_str(Dest, "Multiblock", Options.Multiblock ? "1" : "0");
+    Dest = json_str(Dest, "SilentLog", Options.EnableLogging ? "0" : "1");
+    if (Options.EnableLogging) {
+      Dest = json_str(Dest, "OutputLog", "server");
+    }
     Dest = json_objClose(Dest);
   }
 

Source/Tools/FEXServer/Main.cpp

@@ -206,7 +206,13 @@ int main(int argc, char** argv, char** const envp) {
     LogMan::Msg::DFmt("[FEXServer] Couldn't set subreaper.");
   }
 
-  if (Options.Foreground) {
+  bool EnableLoggingThread = Options.Foreground;
+#ifndef FEX_STEAM_SUPPORT
+  // If running with Steam support then always enable the logging thread.
+  EnableLoggingThread = true;
+#endif
+
+  if (EnableLoggingThread) {
     // Only start a log thread if we are in the foreground.
     // Prevents FEX from trying to log to nothing.
     Logger::StartLogThread();