Added fallbacks for fsync issues on CachyOS.

ptlinux/runtime.py

@@ -7,6 +7,7 @@ from datetime import datetime
 import json
 import os
 from pathlib import Path
+import platform
 import shutil
 import sys
 from typing import Mapping
@@ -25,6 +26,8 @@ WINETRICKS_CODEPAGE_PROBE = (
 	'winetricks_early_wine_arch cmd.exe /c "chcp 65001 > nul & echo %$1%"'
 )
 WINETRICKS_PROTON7_PROBE = 'winetricks_early_wine_arch cmd.exe /c "echo %$1%"'
+RUNTIME_DEFAULT_SYNC = "runtime-default"
+CACHYOS_MARKER = "cachyos"
 
 
 class RuntimeErrorPT(RuntimeError):
@@ -238,7 +241,11 @@ def run_game(
 			WINDOWS_GAME_EXE,
 			"PTEU_REBORN",
 		]
-		environment = _proton_environment(paths, selection)
+		environment = _proton_environment(
+			paths,
+			selection,
+			synchronization=resolve_proton_sync_mode(settings.proton_sync),
+		)
 	if use_gamebox:
 		game_command = build_gamebox_command(game_command, settings)
 	environment["PYTHONPATH"] = _runtime_python_path(
@@ -274,10 +281,12 @@ def _umu_environment(paths: AppPaths) -> dict[str, str]:
 def _proton_environment(
 	paths: AppPaths,
 	selection: RuntimeSelection,
+	*,
+	synchronization: str = RUNTIME_DEFAULT_SYNC,
 ) -> dict[str, str]:
 	if not selection.steam_root:
 		raise RuntimeErrorPT("Steam root is missing for Proton")
-	return {
+	environment = {
 		"STEAM_COMPAT_CLIENT_INSTALL_PATH": selection.steam_root,
 		"STEAM_COMPAT_DATA_PATH": str(paths.compat_data),
 		"STEAM_COMPAT_INSTALL_PATH": str(paths.runtime_view),
@@ -288,6 +297,57 @@ def _proton_environment(
 		"PROTON_LOG": "0",
 		"DXVK_STATE_CACHE_PATH": str(paths.dxvk_cache),
 	}
+	environment.update(_proton_sync_environment(synchronization))
+	return environment
+
+
+def detect_distribution_id() -> str:
+	"""Return the freedesktop distribution ID without invoking distro tools."""
+
+	try:
+		value = platform.freedesktop_os_release().get("ID", "")
+	except OSError:
+		return ""
+	return value.strip().casefold()
+
+
+def resolve_proton_sync_mode(
+	configured: str,
+	*,
+	distribution_id: str | None = None,
+	kernel_release: str | None = None,
+) -> str:
+	"""Resolve the configured mode, applying the narrow CachyOS compatibility fallback."""
+
+	if configured not in {"auto", "fsync", "esync"}:
+		raise ValueError(f"unsupported Proton synchronization mode: {configured}")
+	if configured != "auto":
+		return configured
+	distribution = detect_distribution_id() if distribution_id is None else distribution_id
+	kernel = platform.release() if kernel_release is None else kernel_release
+	if CACHYOS_MARKER in distribution.casefold() or CACHYOS_MARKER in kernel.casefold():
+		return "esync"
+	return RUNTIME_DEFAULT_SYNC
+
+
+def _proton_sync_environment(synchronization: str) -> dict[str, str]:
+	if synchronization == RUNTIME_DEFAULT_SYNC:
+		return {}
+	if synchronization == "esync":
+		return {
+			"PROTON_NO_FSYNC": "1",
+			"WINEFSYNC": "0",
+			"PROTON_NO_ESYNC": "0",
+			"WINEESYNC": "1",
+		}
+	if synchronization == "fsync":
+		return {
+			"PROTON_NO_FSYNC": "0",
+			"WINEFSYNC": "1",
+			"PROTON_NO_ESYNC": "0",
+			"WINEESYNC": "1",
+		}
+	raise ValueError(f"unsupported resolved Proton synchronization mode: {synchronization}")
 
 
 def _ensure_proton_game_link(paths: AppPaths) -> None: