Re: [Qemu-devel] [RFC 13/29] vhost+postcopy: Transmit 'listen' to client

[Maxime Coquelin]

On 06/28/2017 09:00 PM, Dr. David Alan Gilbert (git) wrote:
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index b98fbe4834..1f70f5760f 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -67,6 +67,7 @@ typedef enum VhostUserRequest {
>       VHOST_USER_SET_SLAVE_REQ_FD = 21,
>       VHOST_USER_IOTLB_MSG = 22,
>       VHOST_USER_POSTCOPY_ADVISE  = 23,
> +    VHOST_USER_POSTCOPY_LISTEN  = 24,
>       VHOST_USER_MAX
>   } VhostUserRequest;
>   
> @@ -771,6 +772,25 @@ static int vhost_user_postcopy_advise(struct vhost_dev *dev, Error **errp)
>       return 0;
>   }
>   
> +/*
> + * Called at the switch to postcopy on reception of the 'listen' command.
> + */
> +static int vhost_user_postcopy_listen(struct vhost_dev *dev, Error **errp)
> +{
> +    VhostUserMsg msg = {
> +        .request = VHOST_USER_POSTCOPY_LISTEN,
> +        .flags = VHOST_USER_VERSION,
> +    };

I think it should use REPLY_ACK feature when available for two reasons:
1. The backend could reply nack if nregions is already set.
2. When leaving vhost_user_postcopy_listen(), the message might likely
   not have been handled yet by the backend.

> +    trace_vhost_user_postcopy_listen();
> +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> +        error_setg(errp, "Failed to send postcopy_listen to vhost");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
>   static int vhost_user_postcopy_notifier(NotifierWithReturn *notifier,
>                                           void *opaque)
>   {
> @@ -793,6 +813,9 @@ static int vhost_user_postcopy_notifier(NotifierWithReturn 
> *notifier,
>       case POSTCOPY_NOTIFY_INBOUND_ADVISE:
>           return vhost_user_postcopy_advise(dev, pnd->errp);
>   
> +    case POSTCOPY_NOTIFY_INBOUND_LISTEN:
> +        return vhost_user_postcopy_listen(dev, pnd->errp);
> +
>       default:
>           /* We ignore notifications we don't know */
>           break;