Provide migration_notifier_set_error(), which allows migration notifiers
to return an error message indicating they have failed, which halts the
migration.  The error message is visible in the 'info migrate' command.

No functional change until calls to migration_notifier_set_error are
added.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 include/migration/misc.h |  3 ++-
 migration/migration.c    | 31 +++++++++++++++++++++++++++----
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/include/migration/misc.h b/include/migration/misc.h
index d4c2d7d..e5d8c81 100644
--- a/include/migration/misc.h
+++ b/include/migration/misc.h
@@ -63,7 +63,8 @@ bool migration_is_active(MigrationState *);
 void migration_add_notifier(Notifier *notify,
                             void (*func)(Notifier *notifier, void *data));
 void migration_remove_notifier(Notifier *notify);
-void migration_call_notifiers(MigrationState *s);
+int migration_call_notifiers(MigrationState *s);
+void migration_notifier_set_error(MigrationState *s, Error *err);
 bool migration_in_setup(MigrationState *);
 bool migration_has_finished(MigrationState *);
 bool migration_has_failed(MigrationState *);
diff --git a/migration/migration.c b/migration/migration.c
index 45eebea..d477b58 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1924,6 +1924,8 @@ static void block_cleanup_parameters(MigrationState *s)
 
 static void migrate_fd_cleanup(MigrationState *s)
 {
+    bool already_failed;
+
     qemu_bh_delete(s->cleanup_bh);
     s->cleanup_bh = NULL;
 
@@ -1973,7 +1975,15 @@ static void migrate_fd_cleanup(MigrationState *s)
         /* It is used on info migrate.  We can't free it */
         error_report_err(error_copy(s->error));
     }
-    migration_call_notifiers(s);
+
+    already_failed = migration_has_failed(s);
+    if (migration_call_notifiers(s)) {
+        if (!already_failed) {
+            migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
+            /* Notify again to recover from this late failure. */
+            migration_call_notifiers(s);
+        }
+    }
     block_cleanup_parameters(s);
     cpr_exec();
     yank_unregister_instance(MIGRATION_YANK_INSTANCE);
@@ -2084,9 +2094,16 @@ void migration_remove_notifier(Notifier *notify)
     }
 }
 
-void migration_call_notifiers(MigrationState *s)
+int migration_call_notifiers(MigrationState *s)
 {
     notifier_list_notify(&migration_state_notifiers, s);
+    return (s->error != NULL);
+}
+
+void migration_notifier_set_error(MigrationState *s, Error *err)
+{
+    migrate_set_error(s, err);
+    error_report_err(err);
 }
 
 bool migration_in_setup(MigrationState *s)
@@ -3381,7 +3398,9 @@ static int postcopy_start(MigrationState *ms)
      * spice needs to trigger a transition now
      */
     ms->postcopy_after_devices = true;
-    migration_call_notifiers(ms);
+    if (migration_call_notifiers(ms)) {
+        goto fail;
+    }
 
     ms->downtime =  qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - time_at_stop;
 
@@ -4412,7 +4431,11 @@ void migrate_fd_connect(MigrationState *s, Error *error_in)
         rate_limit = s->parameters.max_bandwidth / XFER_LIMIT_RATIO;
 
         /* Notify before starting migration thread */
-        migration_call_notifiers(s);
+        if (migration_call_notifiers(s)) {
+            migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
+            migrate_fd_cleanup(s);
+            return;
+        }
     }
 
     qemu_file_set_rate_limit(s->to_dst_file, rate_limit);
-- 
1.8.3.1