uefi: Implement SignalEvent() boot services function

uefi-test-runner/src/boot/misc.rs

@@ -17,6 +17,7 @@ pub fn test() {
     info!("Testing events...");
     test_check_event();
     test_callback_with_ctx();
+    test_signal_event();
     info!("Testing watchdog...");
     test_watchdog();
     info!("Testing protocol handler services...");
@@ -92,6 +93,38 @@ fn test_callback_with_ctx() {
     assert_eq!(data, 456);
 }
 
+fn test_signal_event() {
+    let mut data = 123u32;
+
+    extern "efiapi" fn callback(_event: Event, ctx: Option<NonNull<c_void>>) {
+        info!("Inside the signal event callback");
+        // Safety: this callback is run within the parent function's
+        // scope, so the context pointer is still valid.
+        unsafe {
+            let ctx = ctx.unwrap().as_ptr().cast::<u32>();
+            *ctx = 456;
+        }
+    }
+
+    let ctx: *mut u32 = &mut data;
+    let ctx = NonNull::new(ctx.cast::<c_void>()).unwrap();
+
+    let event = unsafe {
+        boot::create_event(
+            EventType::NOTIFY_SIGNAL,
+            Tpl::CALLBACK,
+            Some(callback),
+            Some(ctx),
+        )
+        .expect("Failed to create event with context")
+    };
+
+    boot::signal_event(&event).expect("Failed to signal event");
+
+    // Check that `data` was updated inside the event callback.
+    assert_eq!(data, 456);
+}
+
 fn test_watchdog() {
     // There's no way to check the watchdog timer value, so just test setting it.
 

uefi/CHANGELOG.md

@@ -1,5 +1,8 @@
 # uefi - [Unreleased]
 
+## Added
+- Added `boot::signal_event`.
+
 ## Changed
 - **Breaking:** Removed `BootPolicyError` as `BootPolicy` construction is no
   longer fallible. `BootPolicy` now tightly integrates the new `Boolean` type

uefi/src/boot.rs

@@ -467,6 +467,31 @@ pub fn check_event(event: Event) -> Result<bool> {
     }
 }
 
+/// Places the supplied `event` in the signaled state. If `event` is already in
+/// the signaled state, the function returns successfully. If `event` is of type
+/// [`NOTIFY_SIGNAL`], the event's notification function is scheduled to be
+/// invoked at the event's notification task priority level.
+///
+/// This function may be invoked from any task priority level.
+///
+/// If `event` is part of an event group, then all of the events in the event
+/// group are also signaled and their notification functions are scheduled.
+///
+/// When signaling an event group, it is possible to create an event in the
+/// group, signal it and then close the event to remove it from the group.
+///
+/// # Errors
+///
+/// The specification does not list any errors.
+///
+/// [`NOTIFY_SIGNAL`]: EventType::NOTIFY_SIGNAL
+pub fn signal_event(event: &Event) -> Result {
+    let bt = boot_services_raw_panicking();
+    let bt = unsafe { bt.as_ref() };
+
+    unsafe { (bt.signal_event)(event.as_ptr()) }.to_result()
+}
+
 /// Removes `event` from any event group to which it belongs and closes it.
 ///
 /// If `event` was registered with [`register_protocol_notify`], then the