migration: Refactor migrate_cap_add

Instead of taking a list parameter and returning a new head at a
distance, just return the new item for the caller to insert into a
list via QAPI_LIST_PREPEND.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20201113011340.463563-4-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

migration/migration.c

@@ -1654,27 +1654,23 @@ void migrate_set_state(int *state, int old_state, int new_state)
     }
 }
 
-static MigrationCapabilityStatusList *migrate_cap_add(
-    MigrationCapabilityStatusList *list,
-    MigrationCapability index,
-    bool state)
+static MigrationCapabilityStatus *migrate_cap_add(MigrationCapability index,
+                                                  bool state)
 {
-    MigrationCapabilityStatusList *cap;
+    MigrationCapabilityStatus *cap;
 
-    cap = g_new0(MigrationCapabilityStatusList, 1);
-    cap->value = g_new0(MigrationCapabilityStatus, 1);
-    cap->value->capability = index;
-    cap->value->state = state;
-    cap->next = list;
+    cap = g_new0(MigrationCapabilityStatus, 1);
+    cap->capability = index;
+    cap->state = state;
 
     return cap;
 }
 
 void migrate_set_block_enabled(bool value, Error **errp)
 {
-    MigrationCapabilityStatusList *cap;
+    MigrationCapabilityStatusList *cap = NULL;
 
-    cap = migrate_cap_add(NULL, MIGRATION_CAPABILITY_BLOCK, value);
+    QAPI_LIST_PREPEND(cap, migrate_cap_add(MIGRATION_CAPABILITY_BLOCK, value));
     qmp_migrate_set_capabilities(cap, errp);
     qapi_free_MigrationCapabilityStatusList(cap);
 }
@@ -3863,7 +3859,7 @@ static bool migration_object_check(MigrationState *ms, Error **errp)
 
     for (i = 0; i < MIGRATION_CAPABILITY__MAX; i++) {
         if (ms->enabled_capabilities[i]) {
-            head = migrate_cap_add(head, i, true);
+            QAPI_LIST_PREPEND(head, migrate_cap_add(i, true));
         }
     }