Re: [Qemu-devel] [PATCH v4 1/5] virtio: add "use-started" property

[Greg Kurz <groug@kaod.org>]

On Wed, 26 Jun 2019 10:31:26 +0800
elohimes@gmail.com wrote:

> From: Xie Yongji <xieyongji@baidu.com>
> 
> In order to avoid migration issues, we introduce a "use-started"
> property to the base virtio device to indicate whether use
> "started" flag or not. This property will be true by default and
> set to false when machine type <= 4.0.
> 
> Suggested-by: Greg Kurz <groug@kaod.org>
> Signed-off-by: Xie Yongji <xieyongji@baidu.com>
> ---

LGTM,

Reviewed-by: Greg Kurz <groug@kaod.org>

This fixes the backward migration breakage I was observing.

Tested-by: Greg Kurz <groug@kaod.org>

>  hw/block/vhost-user-blk.c  |  4 ++--
>  hw/core/machine.c          |  1 +
>  hw/virtio/virtio.c         | 18 +++++++-----------
>  include/hw/virtio/virtio.h | 21 +++++++++++++++++++++
>  4 files changed, 31 insertions(+), 13 deletions(-)
> 
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 9cb61336a6..85bc4017e7 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -191,7 +191,7 @@ static void vhost_user_blk_stop(VirtIODevice *vdev)
>  static void vhost_user_blk_set_status(VirtIODevice *vdev, uint8_t status)
>  {
>      VHostUserBlk *s = VHOST_USER_BLK(vdev);
> -    bool should_start = vdev->started;
> +    bool should_start = virtio_device_started(vdev, status);
>      int ret;
>  
>      if (!vdev->vm_running) {
> @@ -317,7 +317,7 @@ static int vhost_user_blk_connect(DeviceState *dev)
>      }
>  
>      /* restore vhost state */
> -    if (vdev->started) {
> +    if (virtio_device_started(vdev, vdev->status)) {
>          ret = vhost_user_blk_start(vdev);
>          if (ret < 0) {
>              error_report("vhost-user-blk: vhost start failed: %s",
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index ea5a01aa49..ea84bd6788 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -30,6 +30,7 @@ GlobalProperty hw_compat_4_0[] = {
>      { "bochs-display",  "edid", "false" },
>      { "virtio-vga",     "edid", "false" },
>      { "virtio-gpu-pci", "edid", "false" },
> +    { "virtio-device", "use-started", "false" },
>  };
>  const size_t hw_compat_4_0_len = G_N_ELEMENTS(hw_compat_4_0);
>  
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index e1e90fcfd6..c9a6ca04b8 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1162,10 +1162,8 @@ int virtio_set_status(VirtIODevice *vdev, uint8_t val)
>              }
>          }
>      }
> -    vdev->started = val & VIRTIO_CONFIG_S_DRIVER_OK;
> -    if (unlikely(vdev->start_on_kick && vdev->started)) {
> -        vdev->start_on_kick = false;
> -    }
> +
> +    virtio_set_started(vdev, val & VIRTIO_CONFIG_S_DRIVER_OK);
>  
>      if (k->set_status) {
>          k->set_status(vdev, val);
> @@ -1536,8 +1534,7 @@ static bool virtio_queue_notify_aio_vq(VirtQueue *vq)
>          ret = vq->handle_aio_output(vdev, vq);
>  
>          if (unlikely(vdev->start_on_kick)) {
> -            vdev->started = true;
> -            vdev->start_on_kick = false;
> +            virtio_set_started(vdev, true);
>          }
>      }
>  
> @@ -1557,8 +1554,7 @@ static void virtio_queue_notify_vq(VirtQueue *vq)
>          vq->handle_output(vdev, vq);
>  
>          if (unlikely(vdev->start_on_kick)) {
> -            vdev->started = true;
> -            vdev->start_on_kick = false;
> +            virtio_set_started(vdev, true);
>          }
>      }
>  }
> @@ -1579,8 +1575,7 @@ void virtio_queue_notify(VirtIODevice *vdev, int n)
>      }
>  
>      if (unlikely(vdev->start_on_kick)) {
> -        vdev->started = true;
> -        vdev->start_on_kick = false;
> +        virtio_set_started(vdev, true);
>      }
>  }
>  
> @@ -2291,7 +2286,7 @@ static void virtio_vmstate_change(void *opaque, int running, RunState state)
>      VirtIODevice *vdev = opaque;
>      BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
>      VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
> -    bool backend_run = running && vdev->started;
> +    bool backend_run = running && virtio_device_started(vdev, vdev->status);
>      vdev->vm_running = running;
>  
>      if (backend_run) {
> @@ -2669,6 +2664,7 @@ static void virtio_device_instance_finalize(Object *obj)
>  
>  static Property virtio_properties[] = {
>      DEFINE_VIRTIO_COMMON_FEATURES(VirtIODevice, host_features),
> +    DEFINE_PROP_BOOL("use-started", VirtIODevice, use_started, true),
>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 27c0efc3d0..15d5366939 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -105,6 +105,7 @@ struct VirtIODevice
>      uint16_t device_id;
>      bool vm_running;
>      bool broken; /* device in invalid state, needs reset */
> +    bool use_started;
>      bool started;
>      bool start_on_kick; /* virtio 1.0 transitional devices support that */
>      VMChangeStateEntry *vmstate;
> @@ -351,4 +352,24 @@ static inline bool virtio_is_big_endian(VirtIODevice *vdev)
>      /* Devices conforming to VIRTIO 1.0 or later are always LE. */
>      return false;
>  }
> +
> +static inline bool virtio_device_started(VirtIODevice *vdev, uint8_t status)
> +{
> +    if (vdev->use_started) {
> +        return vdev->started;
> +    }
> +
> +    return status & VIRTIO_CONFIG_S_DRIVER_OK;
> +}
> +
> +static inline void virtio_set_started(VirtIODevice *vdev, bool started)
> +{
> +    if (started) {
> +        vdev->start_on_kick = false;
> +    }
> +
> +    if (vdev->use_started) {
> +        vdev->started = started;
> +    }
> +}
>  #endif