[Qemu-devel] [PATCH 7/9] migration: Add new migration state wait-unplug

[Jens Freimann <jfreimann@redhat.com>]

This patch is not ready for inclusion yet, I'm looking for
feedback/ideas on a particular problem. See below.

This patch adds a new migration state called wait-unplug.  It is
entered after the SETUP state and 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'.

It adds a new function callback to VMStateDescription which is
called for every device that implements it and reports its
device_pending status.

Now this loop in the migration thread:

while (qemu_savevm_state_guest_unplug_pending()) { continue; }

clearly needs a condition to terminate after a while/or a certain
number of iterations. But I'm not sure what is a good solution. How much
waiting time is acceptable for a migration?

Signed-off-by: Jens Freimann <jfreimann@redhat.com>
---
 include/migration/vmstate.h |  2 ++
 migration/migration.c       | 14 ++++++++++++++
 migration/savevm.c          | 18 ++++++++++++++++++
 migration/savevm.h          |  1 +
 qapi/migration.json         |  5 ++++-
 5 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index c2bfa7a7f0..8b2a125c4c 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -187,6 +187,8 @@ 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;
 };
diff --git a/migration/migration.c b/migration/migration.c
index 8a607fe1e2..a7d21b73fe 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -946,6 +946,9 @@ 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;
 }
@@ -1680,6 +1683,7 @@ 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();
@@ -1712,6 +1716,7 @@ void migrate_init(MigrationState *s)
     error_free(s->error);
     s->error = NULL;
 
+    /* go to WAIT_UNPLUG first? */
     migrate_set_state(&s->state, MIGRATION_STATUS_NONE, MIGRATION_STATUS_SETUP);
 
     s->start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
@@ -3218,6 +3223,15 @@ static void *migration_thread(void *opaque)
 
     qemu_savevm_state_setup(s->to_dst_file);
 
+    migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
+                      MIGRATION_STATUS_WAIT_UNPLUG);
+    while (qemu_savevm_state_guest_unplug_pending()) {
+        continue;
+    }
+    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);
diff --git a/migration/savevm.c b/migration/savevm.c
index 79ed44d475..2bb54b3a8a 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1085,6 +1085,24 @@ void qemu_savevm_state_header(QEMUFile *f)
     }
 }
 
+bool qemu_savevm_state_guest_unplug_pending(void)
+{
+    SaveStateEntry *se;
+    bool ret = false;
+
+    QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
+        if (!se->vmsd || !se->vmsd->dev_unplug_pending) {
+            continue;
+        }
+        ret = se->vmsd->dev_unplug_pending(se->opaque);
+        if (ret) {
+            break;
+        }
+    }
+
+    return ret;
+}
+
 void qemu_savevm_state_setup(QEMUFile *f)
 {
     SaveStateEntry *se;
diff --git a/migration/savevm.h b/migration/savevm.h
index 51a4b9caa8..ba64a7e271 100644
--- a/migration/savevm.h
+++ b/migration/savevm.h
@@ -31,6 +31,7 @@
 
 bool qemu_savevm_state_blocked(Error **errp);
 void qemu_savevm_state_setup(QEMUFile *f);
+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);
diff --git a/qapi/migration.json b/qapi/migration.json
index d567ac9fc3..c42381a85f 100644
--- a/qapi/migration.json
+++ b/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:
-- 
2.21.0