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

Hello Michael,

That was exactly it, just sidestepping an intuitive race with dhcpd writing. Somewhat hypothetical why that would happen, e.g. clustered updates for multiple NICs or whatever similar non-atomicity, but it was easy to express that way, put the update logic in one place (including the initial one at startup), and made the event timestamps sequences a little easier to follow when it wasn't clear why the updates were getting lost at all. I thought the boolean variables helped document the admittedly simple logic too. But none of that is critical.

A

On Mon, Mar 28, 2022, at 1:00 PM, Michael Tremer wrote:

Hello Anthony,

Thank you very much for submitting this patch and welcome to the list.

I understand that it is easier to track any changes in the directory, but I don’t quite understand why the logic had to be changed that the changes will be applied at the end only.

Is this just to avoid that multiple updates happen one after the other or what are you trying to achieve?

-Michael

...

On 22 Mar 2022, at 03:47, Anthony Heading ajrh@ajrh.net wrote:

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