Efficient alias file change detection

[scott-ainsworth]

Currently, avahi-alias-deamon polls for changes to /etc/avahi/avahi-aliases, which is primitive and inefficient. Two possibilities for change detection are subscribing to file system events, signalling, and service restart.

Discussion

Event subscription: File system event subscription is efficient. However, it varies by operating system and can fail (e.g., due to capacity limits). Thus, a fall back is needed. The fall back could be polling or signaling.

Signalling: Sending a daemon a HUP signal is a long-standing method to have a daemon reload data. However, it only notifies under limited circumstances. In this case, when avahi-alias makes changes. Editing the aliases files directly will not send a signal to the daemon. Thus, a fall back is needed. This is likely to be service restart.

Service Restart: This is built in to both systemd and init.d.

Requirements

• Choose a change detection method.
• Implement change detection