A "shadow directory" is now populated when the reload occurs and then swapped as the active directory.
This avoids breaking the directory structure or changing files when other threads are possibly working
on them.
Fixes#3595
Plugins are a convenient way to group together related lua scripts.
Their primary use case is to group user scripts and their alert/status
definition.
The builtin ntopng user scripts and definitions are now
packed into plugins directories. In future, we will support loading of
user created plugins.
Plugins are loaded at startup into some runtime directories and then
used. Other changes provided by this commit include:
- Add sample flow logger plugin
- Initial support for system user scripts
- Rename edge to threshold
- Migrate system probes to user scripts/plugins
- Migrate scripts to more explicit alerts_api.checkThresholdAlert api
