migration: Fail migration blocker for --only-migratable

migrate_add_blocker should rightly fail if the '--only-migratable'
option was specified and the device in use should not be able to
perform the action which results in an unmigratable VM.

Make migrate_add_blocker return -EACCES in this case.
Signed-off-by: NAshijeet Acharya <ashijeetacharya@gmail.com>
Message-Id: <1484566314-3987-6-git-send-email-ashijeetacharya@gmail.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>

include/migration/migration.h

@@ -291,7 +291,7 @@ int ram_postcopy_incoming_init(MigrationIncomingState *mis);
  *
  * @errp - [out] The reason (if any) we cannot block migration right now.
  *
- * @returns - 0 on success, -EBUSY on failure, with errp set.
+ * @returns - 0 on success, -EBUSY/-EACCES on failure, with errp set.
  */
 int migrate_add_blocker(Error *reason, Error **errp);
 

migration/migration.c

@@ -1113,6 +1113,13 @@ static GSList *migration_blockers;
 
 int migrate_add_blocker(Error *reason, Error **errp)
 {
+    if (only_migratable) {
+        error_propagate(errp, error_copy(reason));
+        error_prepend(errp, "disallowing migration blocker "
+                          "(--only_migratable) for: ");
+        return -EACCES;
+    }
+
     if (migration_is_idle(NULL)) {
         migration_blockers = g_slist_prepend(migration_blockers, reason);
         return 0;