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.

Changes since Patch v1:
 * Drop `pub(crate) use crate::bindings::IRQState`.
 * Derefer `slice[0]` directly.
---
 rust/qemu-api/src/irq.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/rust/qemu-api/src/irq.rs b/rust/qemu-api/src/irq.rs
index 835b027d5e5a..05f617b5684a 100644
--- a/rust/qemu-api/src/irq.rs
+++ b/rust/qemu-api/src/irq.rs
@@ -83,6 +83,12 @@ 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 slice_as_ptr(slice: &[Self]) -> *mut *mut IRQState {
+        assert!(!slice.is_empty());
+        slice[0].as_ptr()
+    }
 }
 
 impl Default for InterruptSource {
-- 
2.34.1