Re: [Qemu-devel] [PATCHv2] qdev: DEVICE_DELETED event

[Paolo Bonzini]

Il 06/03/2013 17:55, Michael S. Tsirkin ha scritto:
> On Wed, Mar 06, 2013 at 05:52:05PM +0100, Paolo Bonzini wrote:
>> Il 06/03/2013 17:49, Michael S. Tsirkin ha scritto:
>>> 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 <address@hidden>
>>> ---
>>>
>>> Changes from v1:
>>>     - move to device_unparent
>>>     - address comments by Andreas and Eric
>>>
>>> Andreas also suggested a more generic object-deleted event,
>>> I'm not sure how useful that is so let's add what we already need, for
>>> devices with an id and wait and see what's necessary for non-device
>>> objects?
>>>
>>>  QMP/qmp-events.txt        | 15 +++++++++++++++
>>>  hw/qdev.c                 |  7 +++++++
>>>  include/monitor/monitor.h |  1 +
>>>  monitor.c                 |  1 +
>>>  qapi-schema.json          |  4 +++-
>>>  5 files changed, 27 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/QMP/qmp-events.txt b/QMP/qmp-events.txt
>>> index b2698e4..f2f115a 100644
>>> --- a/QMP/qmp-events.txt
>>> +++ b/QMP/qmp-events.txt
>>> @@ -136,6 +136,21 @@ 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)
>>> +
>>> +{ "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..d603f4f 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;
>>> @@ -761,6 +762,12 @@ static void device_unparent(Object *obj)
>>>      DeviceClass *dc = DEVICE_GET_CLASS(dev);
>>>      BusState *bus;
>>>  
>>> +    if (dev->id) {
>>> +        QObject *data = qobject_from_jsonf("{ 'device': %s }", dev->id);
>>> +        monitor_protocol_event(QEVENT_DEVICE_DELETED, data);
>>> +        qobject_decref(data);
>>> +    }
>>
>> Do this at the end of device_unparent, so that parents are reported
>> after their children.
>>
>> Paolo
> 
> Hmm yes it seems cleaner, though we'd need to copy the
> id as the device can go away.
> 
> Doing this after
>     while (dev->num_child_bus) {
>         bus = QLIST_FIRST(&dev->child_bus);
>         qbus_free(bus); 
>     }
> would be enough, isn't it?

Yes, but don't worry - the device cannot go away, it is protected while
device_unparent is called (see object_unparent in qom/object.c).  So put
it wherever you prefer.

Paolo

>>>      while (dev->num_child_bus) {
>>>          bus = QLIST_FIRST(&dev->child_bus);
>>>          qbus_free(bus);
>>> 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
>>>  ##
>>>