Coding: First Functionality (Slideshow)¶

Todo

jjj add “architecture” drawing

Implement Event List ¶

Right inside the main driver file (refactoring later), define and implement the following artifacts

struct my_event
- Subject to be linked into a list
- Only payload is an enum my_event_type, indicating the event source. We will implement a ioctl request that adds an event to the list, so the only enumerator in the enum will be something like MY_EVENT_IOCTL.
- Will extend to contain a timestamp (jiffies) once we get to it.
struct my_event_list
- Members
  - A struct list_head instance: the real list
  - num_events: counts how many events the list contains
- Methods
  - void my_event_list_init(struct my_event_list* self). The “constructor”; initializes self.
  - void my_event_list_destroy(struct my_event_list* self). The “destructor”; deallocates all events contained in self.
  - void my_event_list_add(struct my_event_list* self, enum my_event_type type). Allocates one event on the heap, initializes it with the given type, and appends it to the list. Once the list exceeds a (hardwired?) maximum event count, the first element in the list is removed.

Start defining an enum, like so:

enum my_ioctl_requests
{
    MY_IOCTL_ADD_EVENT,
};

In the ioctl() driver method, use the above add() method to implement said request.

Write a user space program to exercise that request.
Makes sense to add a number of printk() statements to the kernel to see what is going on.