Re: [PATCH 03/40] vdpa: probe descriptor group index for data vqs

[Jason Wang]

On Fri, Dec 8, 2023 at 2:53 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
> Getting it ahead at initialization time instead of start time allows
> decision making independent of device status, while reducing failure
> possibility in starting device or during migration.
>
> Adding function vhost_vdpa_probe_desc_group() for that end. This
> function will be used to probe the descriptor group for data vqs.
>
> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
> ---
>  net/vhost-vdpa.c | 89 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 89 insertions(+)
>
> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> index 887c329..0cf3147 100644
> --- a/net/vhost-vdpa.c
> +++ b/net/vhost-vdpa.c
> @@ -1688,6 +1688,95 @@ out:
>      return r;
>  }
>
> +static int vhost_vdpa_probe_desc_group(int device_fd, uint64_t features,
> +                                       int vq_index, int64_t *desc_grpidx,
> +                                       Error **errp)
> +{
> +    uint64_t backend_features;
> +    int64_t vq_group, desc_group;
> +    uint8_t saved_status = 0;
> +    uint8_t status = 0;
> +    int r;
> +
> +    ERRP_GUARD();
> +
> +    r = ioctl(device_fd, VHOST_GET_BACKEND_FEATURES, &backend_features);
> +    if (unlikely(r < 0)) {
> +        error_setg_errno(errp, errno, "Cannot get vdpa backend_features");
> +        return r;
> +    }
> +
> +    if (!(backend_features & BIT_ULL(VHOST_BACKEND_F_IOTLB_ASID))) {
> +        return 0;
> +    }
> +
> +    if (!(backend_features & BIT_ULL(VHOST_BACKEND_F_DESC_ASID))) {
> +        return 0;
> +    }
> +
> +    r = ioctl(device_fd, VHOST_VDPA_GET_STATUS, &saved_status);
> +    if (unlikely(r)) {
> +        error_setg_errno(errp, -r, "Cannot get device status");
> +        goto out;
> +    }

I wonder what's the reason for the status being saved and restored?

We don't do this in vhost_vdpa_probe_cvq_isolation().

Thanks