Re: [Qemu-devel] [PATCH 01/15] qdev: do not reset a device until the parent has been initialized

[Paolo Bonzini <pbonzini@redhat.com>]

Il 17/12/2012 17:53, Michael S. Tsirkin ha scritto:
>>> This happens when hotplugging a usb-storage device.  Without this patch,
>>> initialization of a hotplugged usb-storage device would run in pre-order.
>>> Initialization of a coldplugged usb-storage device would run according to
>>> qdev_reset_all semantics (pre-order right now, post-order later in the
>>> series).
>>
>> Is this a problem or just not pretty?

Not pretty.  The child device doesn't exist until the parent has been
initialized, it doesn't make sense to reset it.

I can add an assertion to make it a problem, of course. :)

>>>  This patch makes things consistent.
>>>
>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>> ---
>>>  hw/qdev.c | 5 +++--
>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/hw/qdev.c b/hw/qdev.c
>>> index 599382c..2fdf4ac 100644
>>> --- a/hw/qdev.c
>>> +++ b/hw/qdev.c
>>> @@ -176,8 +176,9 @@ int qdev_init(DeviceState *dev)
>>>                                         dev->alias_required_for_version);
>>>      }
>>>      dev->state = DEV_STATE_INITIALIZED;
>>> -    if (dev->hotplugged) {
>>> -        device_reset(dev);
>>> +    if (dev->hotplugged &&
>>> +        dev->parent_bus->parent->state == DEV_STATE_INITIALIZED) {
>>> +        qdev_reset_all(dev);
>>
>> Let's add a comment explaining the why of this test, and when
>> will reset happen if it does not trigger here.
> 
> Also - shouldn't device init be delayed as well?
> What do you think?

Initialization should run in pre-order (unlike reset): the parent needs
to be ready in order to start the child.  What you typically have, is
that the parent device initializes itself, and then calls
qdev_create/qdev_init on the child before returning.  So it is already
being delayed.  The delay is explicit in program flow, not hidden in
qdev semantics.

Paolo


>>>      }
>>>      return 0;
>>>  }
>>> -- 
>>> 1.8.0.2
>>>