[libvirt] [Qemu-devel] [PATCH v6 1/3] qdev: DEVICE_DELETED event

[Markus Armbruster]

"Michael S. Tsirkin" <mst at redhat.com> writes:

> libvirt has a long-standing bug: when removing the device,
> it can request removal but does not know when the
> removal completes. Add an event so we can fix this in a robust way.
>
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  QMP/qmp-events.txt        | 16 ++++++++++++++++
>  hw/qdev.c                 | 12 ++++++++++++
>  include/monitor/monitor.h |  1 +
>  monitor.c                 |  1 +
>  qapi-schema.json          |  4 +++-
>  5 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/QMP/qmp-events.txt b/QMP/qmp-events.txt
> index b2698e4..24cf3e8 100644
> --- a/QMP/qmp-events.txt
> +++ b/QMP/qmp-events.txt
> @@ -136,6 +136,22 @@ Example:
>  Note: The "ready to complete" status is always reset by a BLOCK_JOB_ERROR
>  event.
>  
> +DEVICE_DELETED
> +-----------------
> +
> +Emitted whenever the device removal completion is acknowledged
> +by the guest.
> +At this point, it's safe to reuse the specified device ID.
> +Device removal can be initiated by the guest or by HMP/QMP commands.
> +
> +Data:
> +
> +- "device": device name (json-string, optional)

If there are no members present, do we get an event without member
"data", or do we get one with an empty member?

    { "event": "DEVICE_DELETED",
      "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }


    { "event": "DEVICE_DELETED",
      "data": { },
      "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }

There's no precedence, as this is the first event with data where all
data members are optional.

> +
> +{ "event": "DEVICE_DELETED",
> +  "data": { "device": "virtio-net-pci-0" },
> +  "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
> +
>  DEVICE_TRAY_MOVED
>  -----------------
>  
> diff --git a/hw/qdev.c b/hw/qdev.c
> index 689cd54..bebc44d 100644
> --- a/hw/qdev.c
> +++ b/hw/qdev.c
> @@ -29,6 +29,7 @@
>  #include "sysemu/sysemu.h"
>  #include "qapi/error.h"
>  #include "qapi/visitor.h"
> +#include "qapi/qmp/qjson.h"
>  
>  int qdev_hotplug = 0;
>  static bool qdev_hot_added = false;
> @@ -760,6 +761,7 @@ static void device_unparent(Object *obj)
>      DeviceState *dev = DEVICE(obj);
>      DeviceClass *dc = DEVICE_GET_CLASS(dev);
>      BusState *bus;
> +    QObject *event_data;
>  
>      while (dev->num_child_bus) {
>          bus = QLIST_FIRST(&dev->child_bus);
> @@ -778,6 +780,16 @@ static void device_unparent(Object *obj)
>          object_unref(OBJECT(dev->parent_bus));
>          dev->parent_bus = NULL;
>      }
> +
> +    if (dev->id) {
> +        event_data = qobject_from_jsonf("{ 'device': %s }", dev->id);
> +    } else {
> +        event_data = NULL;
> +    }
> +    monitor_protocol_event(QEVENT_DEVICE_DELETED, event_data);
> +    if (event_data) {
> +        qobject_decref(event_data);
> +    }

You make this unconditional in 3/3.  Actually, unconditional should work
just fine even here.  No need to respin just for that.

Answering my doc question: we get an event without member "data".

Is that what we want?

>  }
>  
>  static void device_class_init(ObjectClass *class, void *data)
> diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
> index 87fb49c..b868760 100644
> --- a/include/monitor/monitor.h
> +++ b/include/monitor/monitor.h
> @@ -39,6 +39,7 @@ typedef enum MonitorEvent {
>      QEVENT_BLOCK_JOB_CANCELLED,
>      QEVENT_BLOCK_JOB_ERROR,
>      QEVENT_BLOCK_JOB_READY,
> +    QEVENT_DEVICE_DELETED,
>      QEVENT_DEVICE_TRAY_MOVED,
>      QEVENT_SUSPEND,
>      QEVENT_SUSPEND_DISK,
> diff --git a/monitor.c b/monitor.c
> index 32a6e74..2a5e7b6 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -457,6 +457,7 @@ static const char *monitor_event_names[] = {
>      [QEVENT_BLOCK_JOB_CANCELLED] = "BLOCK_JOB_CANCELLED",
>      [QEVENT_BLOCK_JOB_ERROR] = "BLOCK_JOB_ERROR",
>      [QEVENT_BLOCK_JOB_READY] = "BLOCK_JOB_READY",
> +    [QEVENT_DEVICE_DELETED] = "DEVICE_DELETED",
>      [QEVENT_DEVICE_TRAY_MOVED] = "DEVICE_TRAY_MOVED",
>      [QEVENT_SUSPEND] = "SUSPEND",
>      [QEVENT_SUSPEND_DISK] = "SUSPEND_DISK",
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 28b070f..bb361e1 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -2354,7 +2354,9 @@
>  # Notes: When this command completes, the device may not be removed from the
>  #        guest.  Hot removal is an operation that requires guest cooperation.
>  #        This command merely requests that the guest begin the hot removal
> -#        process.
> +#        process.  Completion of the device removal process is signaled with a
> +#        DEVICE_DELETED event. Guest reset will automatically complete removal
> +#        for all devices.
>  #
>  # Since: 0.14.0
>  ##

What do you mean by "Guest reset will automatically complete removal for
all devices"?