Re: [Qemu-devel] [PATCH v4] vhost: Don't abort when vhost-user connection is lost during migration

[Michael S. Tsirkin]

On Fri, Dec 01, 2017 at 01:58:32PM +0800, fangying wrote:
> QEMU will abort when vhost-user process is restarted during migration
> when vhost_log_global_start/stop is called. The reason is clear that
> vhost_dev_set_log returns -1 because network connection is lost.
> 
> To handle this situation, let's cancel migration by setting migrate
> state to failure and report it to user.

In fact I don't see this as the right way to fix it. Backend is dead so why
not just proceed with migration? We just need to make sure we re-send
migration data on re-connect.

> ---
>  hw/virtio/vhost.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index ddc42f0..92725f7 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -26,6 +26,8 @@
>  #include "hw/virtio/virtio-bus.h"
>  #include "hw/virtio/virtio-access.h"
>  #include "migration/blocker.h"
> +#include "migration/migration.h"
> +#include "migration/qemu-file.h"
>  #include "sysemu/dma.h"
>  
>  /* enabled until disconnected backend stabilizes */
> @@ -885,7 +887,10 @@ static void vhost_log_global_start(MemoryListener 
> *listener)
>  
>      r = vhost_migration_log(listener, true);
>      if (r < 0) {
> -        abort();
> +        error_report("Failed to start vhost dirty log");
> +        if (migrate_get_current()->migration_thread_running) {
> +            qemu_file_set_error(migrate_get_current()->to_dst_file, -ECHILD);
> +        }
>      }
>  }
>  
> @@ -895,7 +900,10 @@ static void vhost_log_global_stop(MemoryListener 
> *listener)
>  
>      r = vhost_migration_log(listener, false);
>      if (r < 0) {
> -        abort();
> +        error_report("Failed to stop vhost dirty log");
> +        if (migrate_get_current()->migration_thread_running) {
> +            qemu_file_set_error(migrate_get_current()->to_dst_file, -ECHILD);
> +        }
>      }
>  }
>  
> -- 
> 1.8.3.1
>