Accessing Userspace Memory (Screenplay)¶

New `ioctl`: `GET_ONE_EVENT`¶

Add ioctl
Wonder what the output parameter could be ⟶ discussion
- An event, obviously
- struct my_event has list_head member ⟶ only valid in kernel
- Extract user-relevant data into misc.h: struct my_event is for user, struct my_event_node is for kernel

Getting One Event ¶

Start out like so …

case MY_GET_ONE_EVENT: {
    if (dev->events.nevents > 0) {
        ...
    }
}

⟶ race condition
⟶ new method bool my_device_get_one_event()
- ⟶ new method bool my_event_get_one_event()

`copy_to_user()`¶

Draw diagram, user space memory
Use copy_to_user() to transfer event to userspace
- -EFAULT

Userspace Test Program ¶

trivial