Qt: Support overriding log file on command line

pcsx2-qt/QtHost.cpp

@@ -1595,6 +1595,7 @@ void QtHost::PrintCommandLineHelp(const std::string_view& progname)
 	std::fprintf(stderr, "  -nogui: Hides main window while running (implies batch mode).\n");
 	std::fprintf(stderr, "  -elf <file>: Overrides the boot ELF with the specified filename.\n");
 	std::fprintf(stderr, "  -disc <path>: Uses the specified host DVD drive as a source.\n");
+	std::fprintf(stderr, "  -logfile <path>: Writes the application log to path instead of emulog.txt.\n");
 	std::fprintf(stderr, "  -bios: Starts the BIOS (System Menu/OSDSYS).\n");
 	std::fprintf(stderr, "  -fastboot: Force fast boot for provided filename.\n");
 	std::fprintf(stderr, "  -slowboot: Force slow boot for provided filename.\n");
@@ -1689,6 +1690,11 @@ bool QtHost::ParseCommandLineOptions(const QStringList& args, std::shared_ptr<VM
 				AutoBoot(autoboot)->filename = (++it)->toStdString();
 				continue;
 			}
+			else if (CHECK_ARG_PARAM(QStringLiteral("-logfile")))
+			{
+				CommonHost::SetFileLogPath((++it)->toStdString());
+				continue;
+			}
 			else if (CHECK_ARG(QStringLiteral("-bios")))
 			{
 				AutoBoot(autoboot)->source_type = CDVD_SourceType::NoDisc;

pcsx2/Frontend/LogSink.cpp

@@ -343,7 +343,9 @@ static void UpdateLoggingSinks(bool system_console, bool file_log)
 	{
 		if (!emuLog)
 		{
-			emuLogName = Path::Combine(EmuFolders::Logs, "emulog.txt");
+			if (emuLogName.empty())
+				emuLogName = Path::Combine(EmuFolders::Logs, "emulog.txt");
+
 			emuLog = FileSystem::OpenCFile(emuLogName.c_str(), "wb");
 			file_log = (emuLog != nullptr);
 		}
@@ -365,6 +367,22 @@ static void UpdateLoggingSinks(bool system_console, bool file_log)
 		Console_SetActiveHandler(ConsoleWriter_Null);
 }
 
+void CommonHost::SetFileLogPath(std::string path)
+{
+	if (emuLogName == path)
+		return;
+
+	emuLogName = std::move(path);
+
+	// reopen on change
+	if (emuLog)
+	{
+		std::fclose(emuLog);
+		if (!emuLogName.empty())
+			emuLog = FileSystem::OpenCFile(emuLogName.c_str(), "wb");
+	}
+}
+
 void CommonHost::SetBlockSystemConsole(bool block)
 {
 	s_block_system_console = block;

pcsx2/Frontend/LogSink.h

@@ -19,6 +19,9 @@ class SettingsInterface;
 
 namespace CommonHost
 {
+	/// Overrides the filename used for the file log.
+	void SetFileLogPath(std::string path);
+
 	/// Prevents the system console from being displayed.
 	void SetBlockSystemConsole(bool block);