system/runstate: add VM state change cb with return value

This patch adds the new VM state change cb type `VMChangeStateHandlerWithRet`,
which has return value for `VMChangeStateEntry`.

Thus, we can register a new VM state change cb with return value for device.
Note that `VMChangeStateHandler` and `VMChangeStateHandlerWithRet` are mutually
exclusive and cannot be provided at the same time.

This patch is the pre patch for 'vhost-user: return failure if backend crashes
when live migration', which makes the live migration aware of the loss of
connection with the vhost-user backend and aborts the live migration.

Virtio device will use VMChangeStateHandlerWithRet.

Signed-off-by: Haoqian He <haoqian.he@smartx.com>
Message-Id: <20250416024729.3289157-2-haoqian.he@smartx.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/system/cpus.c b/system/cpus.c
index 2cc5f887ab..d16b0dff98 100644
--- a/system/cpus.c
+++ b/system/cpus.c
@@ -299,14 +299,18 @@ static int do_vm_stop(RunState state, bool send_stop)
         if (oldstate == RUN_STATE_RUNNING) {
             pause_all_vcpus();
         }
-        vm_state_notify(0, state);
+        ret = vm_state_notify(0, state);
         if (send_stop) {
             qapi_event_send_stop();
         }
     }
 
     bdrv_drain_all();
-    ret = bdrv_flush_all();
+    /*
+     * Even if vm_state_notify() return failure,
+     * it would be better to flush as before.
+     */
+    ret |= bdrv_flush_all();
     trace_vm_stop_flush_all(ret);
 
     return ret;