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

[Michael Tremer <michael.tremer@ipfire.org>]

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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(a)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
>