migration: Optimization about wait-unplug migration state

qemu_savevm_nr_failover_devices() is originally designed to
get the number of failover devices, but it actually returns
the number of "unplug-pending" failover devices now. Moreover,
what drives migration state to wait-unplug should be the number
of "unplug-pending" failover devices, not all failover devices.

We can also notice that qemu_savevm_state_guest_unplug_pending()
and qemu_savevm_nr_failover_devices() is equivalent almost (from
the code view). So the latter is incorrect semantically and
useless, just delete it.

In the qemu_savevm_state_guest_unplug_pending(), once hit a
unplug-pending failover device, then it can return true right
now to save cpu time.

Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Tested-by: Jens Freimann <jfreimann@redhat.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/migration.c

@@ -3341,7 +3341,7 @@ static void *migration_thread(void *opaque)
 
     qemu_savevm_state_setup(s->to_dst_file);
 
-    if (qemu_savevm_nr_failover_devices()) {
+    if (qemu_savevm_state_guest_unplug_pending()) {
         migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                           MIGRATION_STATUS_WAIT_UNPLUG);
 

migration/savevm.c

@@ -1140,36 +1140,18 @@ void qemu_savevm_state_header(QEMUFile *f)
     }
 }
 
-int qemu_savevm_nr_failover_devices(void)
+bool qemu_savevm_state_guest_unplug_pending(void)
 {
     SaveStateEntry *se;
-    int n = 0;
 
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
         if (se->vmsd && se->vmsd->dev_unplug_pending &&
             se->vmsd->dev_unplug_pending(se->opaque)) {
-            n++;
-        }
-    }
-
-    return n;
-}
-
-bool qemu_savevm_state_guest_unplug_pending(void)
-{
-    SaveStateEntry *se;
-    int n = 0;
-
-    QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
-        if (!se->vmsd || !se->vmsd->dev_unplug_pending) {
-            continue;
-        }
-        if (se->vmsd->dev_unplug_pending(se->opaque)) {
-            n++;
+            return true;
         }
     }
 
-    return n > 0;
+    return false;
 }
 
 void qemu_savevm_state_setup(QEMUFile *f)

migration/savevm.h

@@ -31,7 +31,6 @@
 
 bool qemu_savevm_state_blocked(Error **errp);
 void qemu_savevm_state_setup(QEMUFile *f);
-int qemu_savevm_nr_failover_devices(void);
 bool qemu_savevm_state_guest_unplug_pending(void);
 int qemu_savevm_state_resume_prepare(MigrationState *s);
 void qemu_savevm_state_header(QEMUFile *f);