migration: per-mode blockers

Extend the blocker interface so that a blocker can be registered for
one or more migration modes.  The existing interfaces register a
blocker for all modes, and the new interfaces take a varargs list
of modes.

Internally, maintain a separate blocker list per mode.  The same Error
object may be added to multiple lists.  When a block is deleted, it is
removed from every list, and the Error is freed.

No functional change until a new mode is added.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <1698263069-406971-3-git-send-email-steven.sistare@oracle.com>
diff --git a/stubs/migr-blocker.c b/stubs/migr-blocker.c
index 17a5dbf..11cbff2 100644
--- a/stubs/migr-blocker.c
+++ b/stubs/migr-blocker.c
@@ -6,6 +6,16 @@
     return 0;
 }
 
+int migrate_add_blocker_normal(Error **reasonp, Error **errp)
+{
+    return 0;
+}
+
+int migrate_add_blocker_modes(Error **reasonp, Error **errp, MigMode mode, ...)
+{
+    return 0;
+}
+
 void migrate_del_blocker(Error **reasonp)
 {
 }