From ace50a79e76dd94661c562283a2f5e51e679db75 Mon Sep 17 00:00:00 2001
From: Disassembler <disassembler@dasm.cz>
Date: Fri, 2 Nov 2018 19:54:20 +0100
Subject: [PATCH] Use file-locking also for config.

---
 usr/lib/python3.6/vmmgr/config.py | 11 +++++++----
 usr/lib/python3.6/vmmgr/tools.py  |  5 ++++-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/usr/lib/python3.6/vmmgr/config.py b/usr/lib/python3.6/vmmgr/config.py
index 4aa0355..5d43ab0 100644
--- a/usr/lib/python3.6/vmmgr/config.py
+++ b/usr/lib/python3.6/vmmgr/config.py
@@ -1,22 +1,25 @@
 # -*- coding: utf-8 -*-
 
+import fcntl
 import json
-from threading import Lock
 
 CONF_FILE = '/etc/vmmgr/config.json'
 
 class Config:
     def __init__(self):
-        self.lock = Lock()
         self.load()
 
     def load(self):
-        with self.lock:
+        # Load configuration from file. Uses file lock as interprocess mutex
+        with open('/var/lock/vmmgr-hosts.lock', 'w') as lock:
+            fcntl.lockf(lock, fcntl.LOCK_EX)
             with open(CONF_FILE, 'r') as f:
                 self.data = json.load(f)
 
     def save(self):
-        with self.lock:
+        # Save configuration to a file. Uses file lock as interprocess mutex
+        with open('/var/lock/vmmgr-hosts.lock', 'w') as lock:
+            fcntl.lockf(lock, fcntl.LOCK_EX)
             with open(CONF_FILE, 'w') as f:
                 json.dump(self.data, f, sort_keys=True, indent=4)
 
diff --git a/usr/lib/python3.6/vmmgr/tools.py b/usr/lib/python3.6/vmmgr/tools.py
index 9decb39..c5ab5bb 100644
--- a/usr/lib/python3.6/vmmgr/tools.py
+++ b/usr/lib/python3.6/vmmgr/tools.py
@@ -113,8 +113,9 @@ def reboot_vm():
 def update_hosts_lease(app, is_request):
     # This is a poor man's DHCP server which uses /etc/hosts as lease database
     # Leases the first unused IP from range 172.17.0.0/16
+    # Uses file lock as interprocess mutex
     ip = None
-    with open('/var/lock/hosts.lock', 'w') as lock:
+    with open('/var/lock/vmmgr-hosts.lock', 'w') as lock:
         fcntl.lockf(lock, fcntl.LOCK_EX)
         with open('/etc/hosts', 'r') as f:
             leases = [l.strip().split(' ', 1) for l in f]
@@ -138,6 +139,8 @@ def set_container_ip(pid, ip):
     subprocess.run(['nsenter', '-a', '-t', pid, '--', '/bin/sh', '-c', cmd])
 
 def clean_ephemeral_layer(app):
+    # Cleans containers ephemeral layer.
+    # This is done early in the container start process, so the inode of the delta0 directory must remain unchanged
     layer = os.path.join('/var/lib/lxc', app, 'delta0')
     if os.path.exists(layer):
         for item in os.scandir(layer):