Writing a custom kernel panic handler routine

The Linux kernel has a powerful feature named notifier chains (the word chains implying the usage of linked lists). It's essentially based upon a publish-and-subscribe model. The subscriber is the component that wants to know when a given asynchronous event occurs; the publisher is the one that pushes the notification that the event did occur. Quite obviously, the subscriber(s) register interest in a given event and supply a callback function. When the event occurs, the notification mechanism invokes the callback. When someone registers itself with a notifier chain, they have subscribed to it and specified a callback function. When the relevant event occurs, all subscribers' callback functions for that notifier chain are invoked (there's even a way to specify your priority and pass some data along, which we'll get to soon enough). We shall make use of one of the kernel's predefined notifier chains – the panic...