Re: vhost-user-blk reconnect issue

[Stefano Garzarella]

Hi Yajun,

On Mon, Mar 25, 2024 at 10:54:13AM +0000, Yajun Wu wrote:
> Hi experts,
>
> With latest QEMU (8.2.90), we find two vhost-user-blk backend reconnect 
> failure scenarios:

Do you know if has it ever worked and so it's a regression, or have we 
always had this problem?

Thanks,
Stefano

> 1. Disconnect vhost-user-blk backend before guest driver probe vblk device, 
> then reconnect backend after guest driver probe device. QEMU won't send out any 
> vhost messages to restore backend.
> This is because vhost->vdev is NULL before guest driver probe vblk device, so 
> vhost_user_blk_disconnect won't be called, s->connected is still true. Next 
> vhost_user_blk_connect will simply return without doing anything.
>
> 2. modprobe -r virtio-blk inside VM, then disconnect backend, then reconnect 
> backend, then modprobe virtio-blk. QEMU won't send messages in vhost_dev_init.
> This is because rmmod will let qemu call vhost_user_blk_stop, vhost->vdev also 
> become NULL(in vhost_dev_stop), vhost_user_blk_disconnect won't be called. Again 
> s->connected is still true, even chr connect is closed.
>
> I think even vhost->vdev is NULL, vhost_user_blk_disconnect should be called 
> when chr connect close?
> Hope we can have a fix soon.
>
>
> Thanks,
> Yajun