Re: [PATCH v5 05/18] qdev: unplug blocker for devices

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Wed, Jan 19, 2022 at 04:41:54PM -0500, Jagannathan Raman wrote:
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> ---
>  include/hw/qdev-core.h |  5 +++++
>  softmmu/qdev-monitor.c | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+)
> 
> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> index eed2983072..67df5e0081 100644
> --- a/include/hw/qdev-core.h
> +++ b/include/hw/qdev-core.h
> @@ -193,6 +193,7 @@ struct DeviceState {
>      int instance_id_alias;
>      int alias_required_for_version;
>      ResettableState reset;
> +    GSList *unplug_blockers;
>  };
>  
>  struct DeviceListener {
> @@ -433,6 +434,10 @@ typedef bool (QDevPutBusFunc)(BusState *bus, Error **errp);
>  bool qdev_set_bus_cbs(QDevGetBusFunc *get_bus, QDevPutBusFunc *put_bus,
>                        Error **errp);
>  
> +int qdev_add_unplug_blocker(DeviceState *dev, Error *reason, Error **errp);
> +void qdev_del_unplug_blocker(DeviceState *dev, Error *reason);
> +bool qdev_unplug_blocked(DeviceState *dev, Error **errp);
> +
>  /**
>   * GpioPolarity: Polarity of a GPIO line
>   *
> diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
> index 7306074019..1a169f89a2 100644
> --- a/softmmu/qdev-monitor.c
> +++ b/softmmu/qdev-monitor.c
> @@ -978,10 +978,45 @@ void qmp_device_del(const char *id, Error **errp)
>              return;
>          }
>  
> +        if (qdev_unplug_blocked(dev, errp)) {
> +            return;
> +        }
> +
>          qdev_unplug(dev, errp);
>      }
>  }
>  
> +int qdev_add_unplug_blocker(DeviceState *dev, Error *reason, Error **errp)
> +{
> +    ERRP_GUARD();
> +
> +    if (!migration_is_idle()) {
> +        error_setg(errp, "migration is in progress");
> +        return -EBUSY;
> +    }

Why can this function not be called during migration?

> +
> +    dev->unplug_blockers = g_slist_prepend(dev->unplug_blockers, reason);
> +
> +    return 0;
> +}
> +
> +void qdev_del_unplug_blocker(DeviceState *dev, Error *reason)
> +{
> +    dev->unplug_blockers = g_slist_remove(dev->unplug_blockers, reason);
> +}
> +
> +bool qdev_unplug_blocked(DeviceState *dev, Error **errp)
> +{
> +    ERRP_GUARD();
> +
> +    if (dev->unplug_blockers) {
> +        error_propagate(errp, error_copy(dev->unplug_blockers->data));
> +        return true;
> +    }
> +
> +    return false;
> +}
> +
>  void hmp_device_add(Monitor *mon, const QDict *qdict)
>  {
>      Error *err = NULL;
> -- 
> 2.20.1
> 

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