rust: add IoMem::offset_ok_of_val

This performs the same function as `IoMem::offset_ok` but when the size
is known only at runtime, for example, with slices (that carry their own
length as a runtime value).

Signed-off-by: Wedson Almeida Filho <[email protected]>

Author: wedsonaf

rust/kernel/io_mem.rs

@@ -173,6 +173,16 @@ impl<const SIZE: usize> IoMem<SIZE> {
         }
     }
 
+    fn offset_ok_of_val<T: ?Sized>(offset: usize, value: &T) -> bool {
+        let value_size = core::mem::size_of_val(value);
+        let value_alignment = core::mem::align_of_val(value);
+        if let Some(end) = offset.checked_add(value_size) {
+            end <= SIZE && offset % value_alignment == 0
+        } else {
+            false
+        }
+    }
+
     const fn check_offset<T>(offset: usize) {
         crate::build_assert!(Self::offset_ok::<T>(offset), "IoMem offset overflow");
     }