proton: Sync pfx creation and create a guard file.

Due to unlucky power off or a crash crash when first starting the game
the prefix can end up in corrupted state with no obvious way of
troubleshooting.

This is an attempt at ensuring that the prefix was created successfully
and force-recreate it if it wasn't.

CW-Bug-Id: #19720

proton

@@ -16,6 +16,7 @@ import subprocess
 import sys
 import tarfile
 import shlex
+import time
 
 from ctypes import CDLL
 from ctypes import CFUNCTYPE
@@ -40,7 +41,7 @@ from random import randrange
 #To enable debug logging, copy "user_settings.sample.py" to "user_settings.py"
 #and edit it if needed.
 
-CURRENT_PREFIX_VERSION="7.0-100"
+CURRENT_PREFIX_VERSION="7.0-101"
 
 PFX="Proton: "
 ld_path_var = "LD_LIBRARY_PATH"
@@ -475,6 +476,7 @@ class CompatData:
     def __init__(self, compatdata):
         self.base_dir = compatdata + "/"
         self.prefix_dir = self.path("pfx/")
+        self.creation_sync_guard = self.path("pfx/creation_sync_guard")
         self.version_file = self.path("version")
         self.config_info_file = self.path("config_info")
         self.tracked_files_file = self.path("tracked_files")
@@ -624,6 +626,13 @@ class CompatData:
                     log("Unable to write new registry file to " + sysreg_fp)
                     pass
 
+            if int(old_proton_maj) < 7 or (int(old_proton_maj) == 7 and
+                                           int(old_proton_min) == 0 and
+                                           int(old_prefix_ver) < 101):
+                with open(self.creation_sync_guard, "w"):
+                    pass
+                os.sync()
+
             stale_builtins = [self.prefix_dir + "/drive_c/windows/system32/amd_ags_x64.dll",
                               self.prefix_dir + "/drive_c/windows/syswow64/amd_ags_x64.dll" ]
             for builtin in stale_builtins:
@@ -783,12 +792,20 @@ class CompatData:
 
             self.upgrade_pfx(old_ver)
 
+            # not fully-created prefix, copy it for future investigation
+            if file_exists(self.prefix_dir, follow_symlinks=True) and not file_exists(self.creation_sync_guard, follow_symlinks=True):
+                shutil.move(self.prefix_dir, self.path(f"corrupted_pfx-{time.time()}.bak"))
+
             if not file_exists(self.prefix_dir, follow_symlinks=True):
                 makedirs(self.prefix_dir + "/drive_c")
                 set_dir_casefold_bit(self.prefix_dir + "/drive_c")
 
-            if not file_exists(self.prefix_dir + "/user.reg", follow_symlinks=True):
                 self.copy_pfx()
+                os.sync()
+
+                with open(self.creation_sync_guard, "x"):
+                    pass
+                os.sync()
 
             self.migrate_user_paths()