rust/vmstate: Fix size field of VMStateField with VMS_ARRAY_OF_POINTER flag

The `size` field of the VMStateField with VMS_ARRAY_OF_POINTER flag
should stores the size of pointer, which depends on platform.

Currently, `*const`, `*mut`, `NonNull`, `Box<>` and their wrapper are
supported, and they have the same size as `usize`.

Store the size (of `usize`) when VMS_ARRAY_OF_POINTER flag is set.

The size may be changed when more smart pointers are supported, but now
the size of "usize" is enough.

Signed-off-by: Zhao Liu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Paolo Bonzini <[email protected]>

Author: trueptolemy

rust/qemu-api/src/vmstate.rs

@@ -256,6 +256,10 @@ impl VMStateField {
         if (self.flags.0 & VMStateFlags::VMS_POINTER.0) != 0 {
             self.flags = VMStateFlags(self.flags.0 & !VMStateFlags::VMS_POINTER.0);
             self.flags = VMStateFlags(self.flags.0 | VMStateFlags::VMS_ARRAY_OF_POINTER.0);
+            // VMS_ARRAY_OF_POINTER flag stores the size of pointer.
+            // FIXME: *const, *mut, NonNull and Box<> have the same size as usize.
+            //        Resize if more smart pointers are supported.
+            self.size = std::mem::size_of::<usize>();
         }
         self.flags = VMStateFlags(self.flags.0 & !VMStateFlags::VMS_SINGLE.0);
         self.flags = VMStateFlags(self.flags.0 | VMStateFlags::VMS_ARRAY.0);