migration: add new migration state wait-unplug

This patch adds a new migration state called wait-unplug.  It is entered
after the SETUP state if failover devices are present. It will transition
into ACTIVE once all devices were succesfully unplugged from the guest.

So if a guest doesn't respond or takes long to honor the unplug request
the user will see the migration state 'wait-unplug'.

In the migration thread we query failover devices if they're are still
pending the guest unplug. When all are unplugged the migration
continues. If one device won't unplug migration will stay in wait_unplug
state.

Signed-off-by: Jens Freimann <jfreimann@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20191029114905.6856-9-jfreimann@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/migration/vmstate.h

@@ -186,6 +186,8 @@ struct VMStateDescription {
     int (*pre_save)(void *opaque);
     int (*post_save)(void *opaque);
     bool (*needed)(void *opaque);
+    bool (*dev_unplug_pending)(void *opaque);
+
     const VMStateField *fields;
     const VMStateDescription **subsections;
 };

migration/migration.c

@@ -52,6 +52,7 @@
 #include "hw/qdev-properties.h"
 #include "monitor/monitor.h"
 #include "net/announce.h"
+#include "qemu/queue.h"
 
 #define MAX_THROTTLE  (32 << 20)      /* Migration transfer speed throttling */
 
@@ -819,6 +820,7 @@ bool migration_is_setup_or_active(int state)
     case MIGRATION_STATUS_SETUP:
     case MIGRATION_STATUS_PRE_SWITCHOVER:
     case MIGRATION_STATUS_DEVICE:
+    case MIGRATION_STATUS_WAIT_UNPLUG:
         return true;
 
     default:
@@ -954,6 +956,9 @@ static void fill_source_migration_info(MigrationInfo *info)
     case MIGRATION_STATUS_CANCELLED:
         info->has_status = true;
         break;
+    case MIGRATION_STATUS_WAIT_UNPLUG:
+        info->has_status = true;
+        break;
     }
     info->status = s->state;
 }
@@ -1694,6 +1699,7 @@ bool migration_is_idle(void)
     case MIGRATION_STATUS_COLO:
     case MIGRATION_STATUS_PRE_SWITCHOVER:
     case MIGRATION_STATUS_DEVICE:
+    case MIGRATION_STATUS_WAIT_UNPLUG:
         return false;
     case MIGRATION_STATUS__MAX:
         g_assert_not_reached();
@@ -3264,6 +3270,19 @@ static void *migration_thread(void *opaque)
 
     qemu_savevm_state_setup(s->to_dst_file);
 
+    if (qemu_savevm_nr_failover_devices()) {
+        migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
+                          MIGRATION_STATUS_WAIT_UNPLUG);
+
+        while (s->state == MIGRATION_STATUS_WAIT_UNPLUG &&
+               qemu_savevm_state_guest_unplug_pending()) {
+            qemu_sem_timedwait(&s->wait_unplug_sem, 250);
+        }
+
+        migrate_set_state(&s->state, MIGRATION_STATUS_WAIT_UNPLUG,
+                MIGRATION_STATUS_ACTIVE);
+    }
+
     s->setup_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) - setup_start;
     migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                       MIGRATION_STATUS_ACTIVE);
@@ -3511,6 +3530,7 @@ static void migration_instance_finalize(Object *obj)
     qemu_mutex_destroy(&ms->qemu_file_lock);
     g_free(params->tls_hostname);
     g_free(params->tls_creds);
+    qemu_sem_destroy(&ms->wait_unplug_sem);
     qemu_sem_destroy(&ms->rate_limit_sem);
     qemu_sem_destroy(&ms->pause_sem);
     qemu_sem_destroy(&ms->postcopy_pause_sem);
@@ -3556,6 +3576,7 @@ static void migration_instance_init(Object *obj)
     qemu_sem_init(&ms->postcopy_pause_rp_sem, 0);
     qemu_sem_init(&ms->rp_state.rp_sem, 0);
     qemu_sem_init(&ms->rate_limit_sem, 0);
+    qemu_sem_init(&ms->wait_unplug_sem, 0);
     qemu_mutex_init(&ms->qemu_file_lock);
 }
 

migration/migration.h

@@ -206,6 +206,9 @@ struct MigrationState
     /* Flag set once the migration thread called bdrv_inactivate_all */
     bool block_inactive;
 
+    /* Migration is waiting for guest to unplug device */
+    QemuSemaphore wait_unplug_sem;
+
     /* Migration is paused due to pause-before-switchover */
     QemuSemaphore pause_sem;
 

migration/savevm.c

@@ -1113,6 +1113,37 @@ void qemu_savevm_state_header(QEMUFile *f)
     }
 }
 
+int qemu_savevm_nr_failover_devices(void)
+{
+    SaveStateEntry *se;
+    int n = 0;
+
+    QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
+        if (se->vmsd && se->vmsd->dev_unplug_pending) {
+            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 n > 0;
+}
+
 void qemu_savevm_state_setup(QEMUFile *f)
 {
     SaveStateEntry *se;

migration/savevm.h

@@ -31,6 +31,8 @@
 
 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);
 int qemu_savevm_state_iterate(QEMUFile *f, bool postcopy);

qapi/migration.json

@@ -133,6 +133,9 @@
 # @device: During device serialisation when pause-before-switchover is enabled
 #        (since 2.11)
 #
+# @wait-unplug: wait for device unplug request by guest OS to be completed.
+#               (since 4.2)
+#
 # Since: 2.3
 #
 ##
@@ -140,7 +143,7 @@
   'data': [ 'none', 'setup', 'cancelling', 'cancelled',
             'active', 'postcopy-active', 'postcopy-paused',
             'postcopy-recover', 'completed', 'failed', 'colo',
-            'pre-switchover', 'device' ] }
+            'pre-switchover', 'device', 'wait-unplug' ] }
 
 ##
 # @MigrationInfo: