Change Event to be FFI-safe using NonNull

CHANGELOG.md

@@ -12,6 +12,7 @@
   `Address` always take a 64-bit value, regardless of target platform.
 - The conversion methods on `DevicePathToText` and `DevicePathFromText`
   now return a `uefi::Result` instead of an `Option`.
+- `Event` is now a newtype around `NonNull<c_void>` instead of `*mut c_void`.
 
 ## uefi-macros - [Unreleased]
 

src/data_types/mod.rs

@@ -37,9 +37,11 @@ impl Handle {
     }
 }
 
-/// Handle to an event structure
+/// Handle to an event structure, guaranteed to be non-null.
+///
+/// If you need to have a nullable event, use `Option<Event>`.
 #[repr(transparent)]
-pub struct Event(*mut c_void);
+pub struct Event(NonNull<c_void>);
 
 impl Event {
     /// Clone this `Event`

src/proto/media/disk.rs

@@ -74,7 +74,7 @@ impl DiskIo {
 #[repr(C)]
 pub struct DiskIo2Token {
     /// Event to be signalled when an asynchronous disk I/O operation completes.
-    pub event: Event,
+    pub event: Option<Event>,
     /// Transaction status code.
     pub transaction_status: Status,
 }

uefi-test-runner/src/proto/media/known_disk.rs

@@ -214,7 +214,7 @@ fn test_raw_disk_io2(handle: Handle, bt: &BootServices) {
             // Initialise the task context
             let mut task = DiskIoTask {
                 token: DiskIo2Token {
-                    event: event.unsafe_clone(),
+                    event: Some(event.unsafe_clone()),
                     transaction_status: uefi::Status::NOT_READY,
                 },
                 buffer: [0; 512],