vmstate: Mark VMStateInfo.get/put() coroutine_mixed_fn

Migration code can run both in coroutine context (the usual case) and
non-coroutine context (at least savevm/loadvm for snapshots). This also
affects the VMState callbacks, and devices must consider this. Change
the callback definition in VMStateInfo to be explicit about it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230905145002.46391-2-kwolf@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

include/migration/vmstate.h

@@ -41,9 +41,11 @@ typedef struct VMStateField VMStateField;
  */
 struct VMStateInfo {
     const char *name;
-    int (*get)(QEMUFile *f, void *pv, size_t size, const VMStateField *field);
-    int (*put)(QEMUFile *f, void *pv, size_t size, const VMStateField *field,
-               JSONWriter *vmdesc);
+    int coroutine_mixed_fn (*get)(QEMUFile *f, void *pv, size_t size,
+                                  const VMStateField *field);
+    int coroutine_mixed_fn (*put)(QEMUFile *f, void *pv, size_t size,
+                                  const VMStateField *field,
+                                  JSONWriter *vmdesc);
 };
 
 enum VMStateFlags {