Re: [PATCH 7/7] vhost-user-blk: Implement reconnection during realize

[Raphael Norwitz <raphael.norwitz@nutanix.com>]

On Wed, Jun 09, 2021 at 05:46:58PM +0200, Kevin Wolf wrote:
> Commit dabefdd6 removed code that was supposed to try reconnecting
> during .realize(), but actually just crashed and had several design
> problems.
> 
> This adds the feature back without the crash in simple cases while also
> fixing some design problems: Reconnection is now only tried if there was
> a problem with the connection and not an error related to the content
> (which would fail again the same way in the next attempt). Reconnection
> is limited to three attempts (four with the initial attempt) so that we
> won't end up in an infinite loop if a problem is permanent. If the
> backend restarts three times in the very short time window of device
> initialisation, we have bigger problems and erroring out is the right
> course of action.
> 
> In the case that a connection error occurs and we reconnect, the error
> message is printed using error_report_err(), but otherwise ignored.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>

> ---
>  hw/block/vhost-user-blk.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index e49d2e4c83..f75a42bc62 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -455,8 +455,10 @@ static int vhost_user_blk_realize_connect(VHostUserBlk *s, Error **errp)
>  
>  static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
>  {
> +    ERRP_GUARD();
>      VirtIODevice *vdev = VIRTIO_DEVICE(dev);
>      VHostUserBlk *s = VHOST_USER_BLK(vdev);
> +    int retries;
>      int i, ret;
>  
>      if (!s->chardev.chr) {
> @@ -498,7 +500,17 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
>      s->inflight = g_new0(struct vhost_inflight, 1);
>      s->vhost_vqs = g_new0(struct vhost_virtqueue, s->num_queues);
>  
> -    ret = vhost_user_blk_realize_connect(s, errp);
> +    retries = 3;
> +    assert(!*errp);
> +    do {
> +        if (*errp) {
> +            error_prepend(errp, "Reconnecting after error: ");
> +            error_report_err(*errp);
> +            *errp = NULL;
> +        }
> +        ret = vhost_user_blk_realize_connect(s, errp);
> +    } while (ret == -EPROTO && retries--);
> +
>      if (ret < 0) {
>          goto virtio_err;
>      }
> -- 
> 2.30.2
>