uefi: Implement SignalEvent() boot services function

Missing from the boot services is the SignalEvent() function, which is used to
place signals into a signaled state. Implement this to allow applications to
signal e.g. event groups.

Also implement a test case, checking that the event callback is signaled when
the newly introduced function is invoked.

Signed-off-by: Bjorn Andersson <[email protected]>

Author: quic-bjorande

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

@@ -10,6 +10,7 @@
 - `SimpleNetwork::transmit` now passes the correct buffer size argument.
   Previously it incorrectly added the header size to the buffer length, which
   could cause the firmware to read past the end of the buffer.
+- `boot::signal_event()` is implemented.
 
 
 # uefi - 0.34.1 (2025-02-07)

uefi/src/boot.rs

@@ -467,6 +467,29 @@ 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.
+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