How do kernel inform OSPF daemon when a physical interface status is down?

When a physical interface status is changed from up to down, there are 3 things related to the computer's current routing table and OSPF.

1. 
   

   The (connected) network for that interface and remote networks that are routed via that (connected) network are removed from the computer's routing table.

   
   


2. 
   

   OSPF neighbors on that (connected) network are removed from the OSPF's neighbors table.

   
   


3. 
   

   Remote networks that are routed via that (connected) network are removed from the OSPF's routing table.

   
   

My question is how do the kernel inform OSPF daemon when a physical interface status is down? It seems like it is a mandatory for the kernel to keep informing the OSPF daemon some information like physical interface status.