Serialize managed Decky changes across desktop and headset

docs/decky-frame.md

@@ -165,6 +165,8 @@ It preserves plugin files and settings so unrelated user data is not deleted.
 Open **Official plugin store** to review a plugin, then confirm each install,
 update, or remove. Root and x86-only plugins are blocked. The manager only
 removes plugin folders that it installed; it leaves other Decky folders alone.
+The desktop app and headset panel share one lock for managed Decky changes.
+If another change is in progress, wait for it to finish and try again.
 Restart Steam or the headset to clear the frontend already injected into its
 current web helper process. No action wipes the headset.
 

tests/test_frame_decky_store.py

@@ -15,6 +15,7 @@ import zipfile
 
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent / 'ui'))
 import frame_decky_store
+import frame_decky
 
 
 def archive(flags=(), extra=None):
@@ -111,6 +112,28 @@ class StoreTransaction(unittest.TestCase):
         self.assertNotEqual(result.returncode, 0)
         self.assertTrue(external.exists())
 
+    def test_shared_lock_rejects_plugin_and_loader_changes(self):
+        import fcntl
+
+        lock_path = Path(self.tmp.name) / '.local/share/frame-control/decky-transaction.lock'
+        lock_path.parent.mkdir(parents=True, exist_ok=True)
+        data, _ = archive()
+        with lock_path.open('w+b') as held:
+            fcntl.flock(held, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            plugin = self.apply('install', data)
+            loader = subprocess.run([sys.executable, '-', 'remove', 'none', 'none', 'none'],
+                                    input=frame_decky.APPLY, text=True, capture_output=True,
+                                    env=self.env, timeout=15)
+            self.assertNotEqual(plugin.returncode, 0)
+            self.assertNotEqual(loader.returncode, 0)
+            self.assertIn('Another Decky change is in progress', plugin.stderr)
+            self.assertIn('Another Decky change is in progress', loader.stderr)
+            self.assertFalse(self.folder.exists())
+
+        installed = self.apply('install', data)
+        self.assertEqual(installed.returncode, 0, installed.stderr)
+        self.assertEqual(self.apply('remove').returncode, 0)
+
 
 class StoreHost(unittest.TestCase):
     def test_owned_plugin_can_be_removed_without_store_network(self):

ui/frame_decky.py

@@ -63,7 +63,7 @@ print(json.dumps({'arch':platform.machine(), 'frameOS':os_release.get('VERSION_I
 
 
 APPLY = r'''
-import hashlib, json, os, pathlib, subprocess, sys
+import fcntl, hashlib, json, os, pathlib, subprocess, sys
 action, token, digest, version = sys.argv[1:]
 home = pathlib.Path.home()
 base = home / '.local/share/frame-control/decky'
@@ -72,6 +72,7 @@ binary = base / 'PluginLoader'
 receipt = base / '.frame-control/receipt.json'
 legacy = base / 'settings/release.json'
 stage = pathlib.Path('/tmp/frame-control-decky-' + token)
+transaction_lock = None
 def systemd(*args):
     p = subprocess.run(['systemctl','--user',*args], capture_output=True, text=True, timeout=20)
     if p.returncode: raise RuntimeError((p.stderr or p.stdout).strip() or 'systemd failed')
@@ -79,6 +80,13 @@ def owned():
     try: return json.loads((receipt if receipt.exists() else legacy).read_text()).get('managedBy') == 'Frame Control' and service.is_file()
     except (OSError, ValueError): return False
 try:
+    # The desktop and headset servers are separate processes. Lock the shared
+    # user-service transaction on the Frame before inspecting or changing it.
+    base.parent.mkdir(parents=True, exist_ok=True)
+    lock_path = base.parent / 'decky-transaction.lock'
+    transaction_lock = os.fdopen(os.open(lock_path, os.O_CREAT | os.O_RDWR | os.O_NOFOLLOW, 0o600), 'r+b')
+    try: fcntl.flock(transaction_lock, fcntl.LOCK_EX | fcntl.LOCK_NB)
+    except BlockingIOError: raise RuntimeError('Another Decky change is in progress; try again after it finishes')
     if action == 'remove':
         if not owned(): raise RuntimeError('No Frame Control managed Decky install to remove')
         systemd('disable','--now','frame-control-decky.service')
@@ -141,6 +149,7 @@ try:
         print(json.dumps({'message':'Decky Loader '+version+' is running as a user service. The VR menu is experimental.'}))
 finally:
     stage.unlink(missing_ok=True)
+    if transaction_lock is not None: transaction_lock.close()
 '''
 
 

ui/frame_decky_store.py

@@ -104,7 +104,7 @@ def archive_info(data, expected_hash, expected_name):
 
 
 APPLY = r'''
-import hashlib,json,pathlib,shutil,subprocess,sys,zipfile
+import fcntl,hashlib,json,os,pathlib,shutil,subprocess,sys,zipfile
 action,token,plugin_id,digest,folder,version = sys.argv[1:]
 base=pathlib.Path.home()/'.local/share/frame-control/decky/plugins'
 unit=pathlib.Path.home()/'.config/systemd/user/frame-control-decky.service'
@@ -113,6 +113,7 @@ archive=pathlib.Path('/tmp/frame-control-decky-plugin-'+token)
 stage=base/('.frame-control-stage-'+token)
 backup=base/('.frame-control-old-'+token)
 marker='.frame-control-store.json'
+transaction_lock=None
 def owned():
     if target.is_symlink() or not target.is_dir(): return False
     try: return json.loads((target/marker).read_text()).get('storeId') == int(plugin_id)
@@ -120,12 +121,19 @@ def owned():
 def service(*args):
     p=subprocess.run(['systemctl','--user',*args],capture_output=True,text=True,timeout=25)
     if p.returncode: raise RuntimeError((p.stderr or p.stdout).strip()[-400:] or 'Decky service failed')
-if not unit.is_file(): raise RuntimeError('Install Frame Control managed Decky first')
-if action not in ('install','update','remove'): raise RuntimeError('Invalid plugin action')
-if action=='install' and (target.exists() or target.is_symlink()): raise RuntimeError('Plugin folder already exists')
-if action in ('update','remove') and not owned(): raise RuntimeError('Only a Frame Control store plugin can be changed')
-running=subprocess.run(['systemctl','--user','is-active','--quiet','frame-control-decky.service']).returncode==0
 try:
+    # A desktop request and a headset-panel request must not change the same
+    # Decky user service at once. Keep this lock until rollback/cleanup ends.
+    base.parent.parent.mkdir(parents=True,exist_ok=True)
+    lock_path=base.parent.parent/'decky-transaction.lock'
+    transaction_lock=os.fdopen(os.open(lock_path,os.O_CREAT|os.O_RDWR|os.O_NOFOLLOW,0o600),'r+b')
+    try: fcntl.flock(transaction_lock,fcntl.LOCK_EX|fcntl.LOCK_NB)
+    except BlockingIOError: raise RuntimeError('Another Decky change is in progress; try again after it finishes')
+    if not unit.is_file(): raise RuntimeError('Install Frame Control managed Decky first')
+    if action not in ('install','update','remove'): raise RuntimeError('Invalid plugin action')
+    if action=='install' and (target.exists() or target.is_symlink()): raise RuntimeError('Plugin folder already exists')
+    if action in ('update','remove') and not owned(): raise RuntimeError('Only a Frame Control store plugin can be changed')
+    running=subprocess.run(['systemctl','--user','is-active','--quiet','frame-control-decky.service']).returncode==0
     if action!='remove':
         data=archive.read_bytes()
         if not 1024<len(data)<=50*1024*1024 or hashlib.sha256(data).hexdigest()!=digest:
@@ -159,6 +167,7 @@ try:
 finally:
     archive.unlink(missing_ok=True)
     if stage.exists(): shutil.rmtree(stage)
+    if transaction_lock is not None: transaction_lock.close()
 '''