Re: [PATCH 01/33] vhost: introduce vhost_ops->vhost_set_vring_enable_supported method

[Raphael Norwitz <raphael.s.norwitz@gmail.com>]

On Wed, Aug 13, 2025 at 12:53 PM Vladimir Sementsov-Ogievskiy
<vsementsov@yandex-team.ru> wrote:
>
> Remove vhost-user specific hack from generic code.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>  hw/virtio/vhost-user.c            |  8 ++++++++
>  hw/virtio/vhost.c                 | 15 ++++++---------
>  include/hw/virtio/vhost-backend.h |  2 ++
>  3 files changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 1e1d6b0d6e..1b2879a90c 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -1230,6 +1230,12 @@ static int vhost_user_set_vring_base(struct vhost_dev *dev,
>      return vhost_set_vring(dev, VHOST_USER_SET_VRING_BASE, ring, false);
>  }
>
> +static bool vhost_user_set_vring_enable_supported(struct vhost_dev *dev)
> +{
> +    return virtio_has_feature(dev->backend_features,
> +                              VHOST_USER_F_PROTOCOL_FEATURES);
> +}
> +
>  static int vhost_user_set_vring_enable(struct vhost_dev *dev, int enable)
>  {
>      int i;
> @@ -3032,6 +3038,8 @@ const VhostOps user_ops = {
>          .vhost_reset_device = vhost_user_reset_device,
>          .vhost_get_vq_index = vhost_user_get_vq_index,
>          .vhost_set_vring_enable = vhost_user_set_vring_enable,
> +        .vhost_set_vring_enable_supported =
> +            vhost_user_set_vring_enable_supported,

Why not make this a callback like vhost_user_gpu_{set|shared}_socket()
in vhost_backend.h instead?


>          .vhost_requires_shm_log = vhost_user_requires_shm_log,
>          .vhost_migration_done = vhost_user_migration_done,
>          .vhost_net_set_mtu = vhost_user_net_set_mtu,
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 6557c58d12..c33dad4acd 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1986,15 +1986,12 @@ static int vhost_dev_set_vring_enable(struct vhost_dev *hdev, int enable)
>          return 0;
>      }
>
> -    /*
> -     * For vhost-user devices, if VHOST_USER_F_PROTOCOL_FEATURES has not
> -     * been negotiated, the rings start directly in the enabled state, and
> -     * .vhost_set_vring_enable callback will fail since
> -     * VHOST_USER_SET_VRING_ENABLE is not supported.
> -     */
> -    if (hdev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER &&
> -        !virtio_has_feature(hdev->backend_features,
> -                            VHOST_USER_F_PROTOCOL_FEATURES)) {
> +    if (hdev->vhost_ops->vhost_set_vring_enable_supported &&
> +        !hdev->vhost_ops->vhost_set_vring_enable_supported(hdev)) {
> +        /*
> +         * This means, that rings are always enabled, and disable/enable
> +         * API is not supported.
> +         */
>          return 0;
>      }
>
> diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
> index d6df209a2f..f65fa26298 100644
> --- a/include/hw/virtio/vhost-backend.h
> +++ b/include/hw/virtio/vhost-backend.h
> @@ -105,6 +105,7 @@ typedef int (*vhost_reset_device_op)(struct vhost_dev *dev);
>  typedef int (*vhost_get_vq_index_op)(struct vhost_dev *dev, int idx);
>  typedef int (*vhost_set_vring_enable_op)(struct vhost_dev *dev,
>                                           int enable);
> +typedef bool (*vhost_set_vring_enable_supported_op)(struct vhost_dev *dev);
>  typedef bool (*vhost_requires_shm_log_op)(struct vhost_dev *dev);
>  typedef int (*vhost_migration_done_op)(struct vhost_dev *dev,
>                                         char *mac_addr);
> @@ -193,6 +194,7 @@ typedef struct VhostOps {
>      vhost_reset_device_op vhost_reset_device;
>      vhost_get_vq_index_op vhost_get_vq_index;
>      vhost_set_vring_enable_op vhost_set_vring_enable;
> +    vhost_set_vring_enable_supported_op vhost_set_vring_enable_supported;
>      vhost_requires_shm_log_op vhost_requires_shm_log;
>      vhost_migration_done_op vhost_migration_done;
>      vhost_vsock_set_guest_cid_op vhost_vsock_set_guest_cid;
> --
> 2.48.1
>
>