[PATCH 1/3] unbound-dhcp-leases-bridge : fix bug 12694 - DHCP hosts not reliably propagated to DNS

[Anthony Heading <ajrh@ajrh.net>]

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Switch from inotify watching individual files to monitoring the
containing directories, as because dhcpd renames its leases file into a
backup, monitoring the single inode does not work well.  Additionally,
python appears to have a bug with replacing expired inotify watches on
single files.
---
 unbound-dhcp-leases-bridge | 47 +++++++++++++++++++++++++-------------
 1 file changed, 31 insertions(+), 16 deletions(-)

diff --git unbound-dhcp-leases-bridge unbound-dhcp-leases-bridge
index a2df5f1..6e22066 100644
--- unbound-dhcp-leases-bridge
+++ unbound-dhcp-leases-bridge
@@ -72,6 +72,15 @@ class UnboundDHCPLeasesBridge(object):
 		self.fix_leases_file = fix_leases_file
 		self.hosts_file = hosts_file
 
+		# base mask for a completed file change
+		mask = inotify.constants.IN_CLOSE_WRITE | inotify.constants.IN_MOVED_TO
+		# IN_MODIFY since dhcpd appends lease updates to an open file
+		self.watches = {
+		    self.leases_file: mask | inotify.constants.IN_MODIFY,
+		    self.fix_leases_file: mask,
+		    self.hosts_file: mask
+		}
+
 		self.unbound = UnboundConfigWriter(unbound_leases_file)
 		self.running = False
 
@@ -80,36 +89,42 @@ class UnboundDHCPLeasesBridge(object):
 		self.running = True
 
 		# Initial setup
-		self.hosts = self.read_static_hosts()
-		self.update_dhcp_leases()
+		update_hosts = True
+		update_leases = True
+
+		i = inotify.adapters.Inotify()
 
-		i = inotify.adapters.Inotify([
-			self.leases_file,
-			self.fix_leases_file,
-			self.hosts_file,
-		])
+		for f in self.watches:
+			i.add_watch(os.path.dirname(f), self.watches[f])
 
 		for event in i.event_gen():
 			# End if we are requested to terminate
 			if not self.running:
 				break
 
+			# Make pending updates once inotify queue is empty
 			if event is None:
+				if update_hosts:
+					self.hosts = self.read_static_hosts()
+					update_hosts = False
+				if update_leases:
+					self.update_dhcp_leases()
+					update_leases = False
 				continue
 
 			header, type_names, watch_path, filename = event
 
-			# Update leases after leases file has been modified
-			if "IN_MODIFY" in type_names:
-				# Reload hosts
-				if watch_path == self.hosts_file:
-					self.hosts = self.read_static_hosts()
+			file = os.path.join(watch_path, filename)
+
+			if not file in self.watches:
+				continue
+
+			log.debug("Inotify %s: %s", file, " ".join(type_names))
 
-				self.update_dhcp_leases()
+			update_leases = True
 
-			# If the file is deleted, we re-add the watcher
-			if "IN_IGNORED" in type_names:
-				i.add_watch(watch_path)
+			if file == self.hosts_file:
+				update_hosts = True
 
 		log.info("Unbound DHCP Leases Bridge terminated")
 
-- 
2.34.1