[PATCH 03/10] rust/irq: Add a helper to convert [InterruptSource] to [*mut IRQState]

[Zhao Liu <zhao1.liu@intel.com>]

This is useful to hanlde InterruptSource slice and pass it to C
bindings.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
Changes since RFC:
 * New commit.
---
 rust/qemu-api/src/irq.rs | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/rust/qemu-api/src/irq.rs b/rust/qemu-api/src/irq.rs
index 638545c3a649..7dca3b9ee5a8 100644
--- a/rust/qemu-api/src/irq.rs
+++ b/rust/qemu-api/src/irq.rs
@@ -5,12 +5,10 @@
 //! Bindings for interrupt sources
 
 use core::ptr;
-use std::{marker::PhantomData, os::raw::c_int};
+use std::{marker::PhantomData, os::raw::c_int, slice};
 
-use crate::{
-    bindings::{qemu_set_irq, IRQState},
-    prelude::*,
-};
+pub(crate) use crate::bindings::IRQState;
+use crate::{bindings::qemu_set_irq, prelude::*};
 
 /// Interrupt sources are used by devices to pass changes to a value (typically
 /// a boolean).  The interrupt sink is usually an interrupt controller or
@@ -81,6 +79,16 @@ pub fn set(&self, level: T) {
     pub(crate) const fn as_ptr(&self) -> *mut *mut IRQState {
         self.cell.as_ptr()
     }
+
+    #[allow(dead_code)]
+    pub(crate) fn as_slice_of_qemu_irq(slice: &[Self]) -> &[*mut IRQState] {
+        unsafe {
+            // SAFETY: InterruptSource has the same memory layout as *mut IRQState.
+            // Additionally, the slice parameter itself, as a reference to a slice type,
+            // can be converted into a valid pointer and has a valid length.
+            slice::from_raw_parts(slice.as_ptr().cast::<*mut IRQState>(), slice.len())
+        }
+    }
 }
 
 impl Default for InterruptSource {
-- 
2.34.1