[PATCH 1/7] rust: bql: add BqlRefCell::get_mut()

[Paolo Bonzini <pbonzini@redhat.com>]

This method is rarely useful in QEMU due to the pervasiveness of
shared references, but add it for when a &mut BqlRefCell<> is used.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 rust/bql/src/cell.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/rust/bql/src/cell.rs b/rust/bql/src/cell.rs
index 24ab294b60d..8a0c8c14ad4 100644
--- a/rust/bql/src/cell.rs
+++ b/rust/bql/src/cell.rs
@@ -580,6 +580,25 @@ pub fn borrow_mut(&self) -> BqlRefMut<'_, T> {
         }
     }
 
+    /// Returns a mutable reference to the underlying data in this cell,
+    /// while the owner already has a mutable reference to the cell.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bql::BqlRefCell;
+    ///
+    /// let mut c = BqlRefCell::new(5);
+    ///
+    /// *c.get_mut() = 10;
+    /// ```
+    #[inline]
+    pub const fn get_mut(&mut self) -> &mut T {
+        // SAFETY: there cannot be any outstanding borrow,
+        // since `self` is mutably owned.
+        unsafe { &mut *self.as_ptr() }
+    }
+
     /// Returns a raw pointer to the underlying data in this cell.
     ///
     /// # Examples
-- 
2.51.0