Re: [PATCH v4 1/2] vhost: dirty log should be per backend type

[Jason Wang <jasowang@redhat.com>]

On Fri, Mar 15, 2024 at 5:39 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
> There could be a mix of both vhost-user and vhost-kernel clients
> in the same QEMU process, where separate vhost loggers for the
> specific vhost type have to be used. Make the vhost logger per
> backend type, and have them properly reference counted.

It's better to describe what's the advantage of doing this.

>
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
>
> ---
> v3->v4:
>   - remove checking NULL return value from vhost_log_get
>
> v2->v3:
>   - remove non-effective assertion that never be reached
>   - do not return NULL from vhost_log_get()
>   - add neccessary assertions to vhost_log_get()
> ---
>  hw/virtio/vhost.c | 45 +++++++++++++++++++++++++++++++++------------
>  1 file changed, 33 insertions(+), 12 deletions(-)
>
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 2c9ac79..612f4db 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -43,8 +43,8 @@
>      do { } while (0)
>  #endif
>
> -static struct vhost_log *vhost_log;
> -static struct vhost_log *vhost_log_shm;
> +static struct vhost_log *vhost_log[VHOST_BACKEND_TYPE_MAX];
> +static struct vhost_log *vhost_log_shm[VHOST_BACKEND_TYPE_MAX];
>
>  /* Memslots used by backends that support private memslots (without an fd). */
>  static unsigned int used_memslots;
> @@ -287,6 +287,10 @@ static int vhost_set_backend_type(struct vhost_dev *dev,
>          r = -1;
>      }
>
> +    if (r == 0) {
> +        assert(dev->vhost_ops->backend_type == backend_type);
> +    }
> +

Under which condition could we hit this? It seems not good to assert a
local logic.

Thanks