///
/// The callback will fire once immediately with an initial interface list, and a diff as if
/// there were originally no interfaces present.
+///
+/// This function will return an error if there is a problem configuring the watcher, or if there
+/// is an error retrieving the initial interface list.
+///
+/// We assume that if listing the interfaces worked the first time, then it will continue to work
+/// for as long as the watcher is running. If listing interfaces begins to fail later, those
+/// failures will be swallowed and the callback will not be called for that change event.
pub fn watch_interfaces<F: FnMut(Update) + Send + 'static>(
callback: F,
) -> Result<WatchHandle, Error> {