Re: [PATCH v2 4/6] qapi: introduce device-sync-config

[Markus Armbruster <armbru@redhat.com>]

Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:

> Add command to sync config from vhost-user backend to the device. It
> may be helpful when VHOST_USER_SLAVE_CONFIG_CHANGE_MSG failed or not
> triggered interrupt to the guest or just not available (not supported
> by vhost-user server).
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>  hw/block/vhost-user-blk.c | 27 ++++++++++++++++++++-------
>  hw/virtio/virtio-pci.c    |  9 +++++++++
>  include/hw/qdev-core.h    |  3 +++
>  qapi/qdev.json            | 17 +++++++++++++++++
>  system/qdev-monitor.c     | 23 +++++++++++++++++++++++
>  5 files changed, 72 insertions(+), 7 deletions(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 9e6bbc6950..2f301f380c 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -88,27 +88,39 @@ static void vhost_user_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
>      s->blkcfg.wce = blkcfg->wce;
>  }
>  
> +static int vhost_user_blk_sync_config(DeviceState *dev, Error **errp)
> +{
> +    int ret;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> +    VHostUserBlk *s = VHOST_USER_BLK(vdev);
> +
> +    ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
> +                               vdev->config_len, errp);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    memcpy(vdev->config, &s->blkcfg, vdev->config_len);
> +    virtio_notify_config(vdev);
> +
> +    return 0;
> +}
> +
>  static int vhost_user_blk_handle_config_change(struct vhost_dev *dev)
>  {
>      int ret;
> -    VirtIODevice *vdev = dev->vdev;
> -    VHostUserBlk *s = VHOST_USER_BLK(dev->vdev);
>      Error *local_err = NULL;
>  
>      if (!dev->started) {
>          return 0;
>      }
>  
> -    ret = vhost_dev_get_config(dev, (uint8_t *)&s->blkcfg,
> -                               vdev->config_len, &local_err);
> +    ret = vhost_user_blk_sync_config(DEVICE(dev->vdev), &local_err);
>      if (ret < 0) {
>          error_report_err(local_err);
>          return ret;
>      }
>  
> -    memcpy(dev->vdev->config, &s->blkcfg, vdev->config_len);
> -    virtio_notify_config(dev->vdev);
> -
>      return 0;
>  }
>  
> @@ -576,6 +588,7 @@ static void vhost_user_blk_class_init(ObjectClass *klass, void *data)
>  
>      device_class_set_props(dc, vhost_user_blk_properties);
>      dc->vmsd = &vmstate_vhost_user_blk;
> +    dc->sync_config = vhost_user_blk_sync_config;
>      set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
>      vdc->realize = vhost_user_blk_device_realize;
>      vdc->unrealize = vhost_user_blk_device_unrealize;
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 1a7039fb0c..1197341a3c 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -2318,6 +2318,14 @@ static void virtio_pci_dc_realize(DeviceState *qdev, Error **errp)
>      vpciklass->parent_dc_realize(qdev, errp);
>  }
>  
> +static int virtio_pci_sync_config(DeviceState *dev, Error **errp)
> +{
> +    VirtIOPCIProxy *proxy = VIRTIO_PCI(dev);
> +    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
> +
> +    return qdev_sync_config(DEVICE(vdev), errp);
> +}
> +
>  static void virtio_pci_class_init(ObjectClass *klass, void *data)
>  {
>      DeviceClass *dc = DEVICE_CLASS(klass);
> @@ -2334,6 +2342,7 @@ static void virtio_pci_class_init(ObjectClass *klass, void *data)
>      device_class_set_parent_realize(dc, virtio_pci_dc_realize,
>                                      &vpciklass->parent_dc_realize);
>      rc->phases.hold = virtio_pci_bus_reset_hold;
> +    dc->sync_config = virtio_pci_sync_config;
>  }
>  
>  static const TypeInfo virtio_pci_info = {
> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> index 9228e96c87..87135bdcdf 100644
> --- a/include/hw/qdev-core.h
> +++ b/include/hw/qdev-core.h
> @@ -95,6 +95,7 @@ typedef void (*DeviceUnrealize)(DeviceState *dev);
>  typedef void (*DeviceReset)(DeviceState *dev);
>  typedef void (*BusRealize)(BusState *bus, Error **errp);
>  typedef void (*BusUnrealize)(BusState *bus);
> +typedef int (*DeviceSyncConfig)(DeviceState *dev, Error **errp);
>  
>  /**
>   * struct DeviceClass - The base class for all devices.
> @@ -162,6 +163,7 @@ struct DeviceClass {
>      DeviceReset reset;
>      DeviceRealize realize;
>      DeviceUnrealize unrealize;
> +    DeviceSyncConfig sync_config;
>  
>      /**
>       * @vmsd: device state serialisation description for
> @@ -546,6 +548,7 @@ bool qdev_hotplug_allowed(DeviceState *dev, Error **errp);
>   */
>  HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev);
>  void qdev_unplug(DeviceState *dev, Error **errp);
> +int qdev_sync_config(DeviceState *dev, Error **errp);
>  void qdev_simple_device_unplug_cb(HotplugHandler *hotplug_dev,
>                                    DeviceState *dev, Error **errp);
>  void qdev_machine_creation_done(void);
> diff --git a/qapi/qdev.json b/qapi/qdev.json
> index 32ffaee644..6ece164172 100644
> --- a/qapi/qdev.json
> +++ b/qapi/qdev.json
> @@ -162,3 +162,20 @@
>  ##
>  { 'event': 'DEVICE_UNPLUG_GUEST_ERROR',
>    'data': { '*device': 'str', 'path': 'str' } }
> +
> +##
> +# @device-sync-config:
> +#
> +# Synchronize config from backend to the guest.
> +#
> +# @id: the device's ID or QOM path
> +#
> +# Features:
> +#
> +# @unstable: The command is experimental.
> +#
> +# Since: 9.0
> +##

Even for an experimental command a bit more guidance on intended would
be good.

The commit message describes this as a "command to sync config from
vhost-user backend to the device".  Here, there's no mention of
vhost-user.

Could the command make sense for devices other than vhost-user?

> +{ 'command': 'device-sync-config',
> +  'features': [ 'unstable' ],
> +  'data': {'id': 'str'} }
> diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
> index cf7481e416..e3107a12d7 100644
> --- a/system/qdev-monitor.c
> +++ b/system/qdev-monitor.c
> @@ -968,6 +968,29 @@ void qmp_device_del(const char *id, Error **errp)
>      }
>  }
>  
> +int qdev_sync_config(DeviceState *dev, Error **errp)
> +{
> +    DeviceClass *dc = DEVICE_GET_CLASS(dev);
> +
> +    if (!dc->sync_config) {
> +        error_setg(errp, "device-sync-config is not supported for '%s'",
> +                   object_get_typename(OBJECT(dev)));
> +        return -ENOTSUP;
> +    }
> +
> +    return dc->sync_config(dev, errp);
> +}
> +
> +void qmp_device_sync_config(const char *id, Error **errp)
> +{
> +    DeviceState *dev = find_device_state(id, true, errp);
> +    if (!dev) {
> +        return;
> +    }
> +
> +    qdev_sync_config(dev, errp);
> +}
> +
>  void hmp_device_add(Monitor *mon, const QDict *qdict)
>  {
>      Error *err = NULL;