Re: [Qemu-devel] [PATCH] qdev: Reset hotplugged devices

[Markus Armbruster]

Anthony Liguori <address@hidden> writes:

> On 08/20/2010 10:47 AM, Markus Armbruster wrote:
>> Alex Williamson<address@hidden>  writes:
>>
>>    
>>> On Fri, 2010-08-20 at 11:00 +0200, Markus Armbruster wrote:
>>>      
>>>> Alex Williamson<address@hidden>  writes:
>>>>
>>>>        
>>>>> Several devices rely on their reset() function being called to
>>>>> initialize device state, e1000 and rtl8139 in particular.  When
>>>>> the device is hot added, the reset doesn't occur, often leaving
>>>>> the device in an unusable state.  Adding a call to reset() after
>>>>> init() for hotplugged devices puts the device in the expected
>>>>> state for the guest.
>>>>>
>>>>> Signed-off-by: Alex Williamson<address@hidden>
>>>>> ---
>>>>>
>>>>>   0.13 candidate?
>>>>>
>>>>>   hw/qdev.c |    3 +++
>>>>>   1 files changed, 3 insertions(+), 0 deletions(-)
>>>>>
>>>>> diff --git a/hw/qdev.c b/hw/qdev.c
>>>>> index e99c73f..b156272 100644
>>>>> --- a/hw/qdev.c
>>>>> +++ b/hw/qdev.c
>>>>> @@ -278,6 +278,9 @@ int qdev_init(DeviceState *dev)
>>>>>           qdev_free(dev);
>>>>>           return rc;
>>>>>       }
>>>>> +    if (dev->hotplugged) {
>>>>> +        qdev_reset(dev);
>>>>> +    }
>>>>>       qemu_register_reset(qdev_reset, dev);
>>>>>       if (dev->info->vmsd) {
>>>>>           vmstate_register_with_alias_id(dev, -1, dev->info->vmsd, dev,
>>>>>          
>>>> qdev_reset() isn't necessary when !dev->hotplugged, because then
>>>> qemu_system_reset() will run shortly, which will call qdev_reset().
>>>> Correct?
>>>>        
>>> Yes, exactly.
>>>      
>> Hmm.  "qdev_init() automatically calls qdev_reset() if hotplug" feels
>> needlessly complicated.  I'd prefer qdev_init() to call it always or
>> never.
>>
>> If "always", we reset twice for cold-plug.  Is that bad?
>>
>> If "never", we need to reset somewhere else for hot-plug.  What about
>> do_device_add()?
>>    
>
> The real problem is how we do reset.  We shouldn't register a reset
> handler for every qdev device but rather register a single reset
> handler that walks the device tree and calls reset on every reachable
> device.
>
> Then we can always call reset in init() and there's no need to have a
> dev->hotplugged check.  The qdev device tree reset handler should not
> be registered until *after* we call qemu_system_reset() after creating
> the device model which will ensure that we don't do a double reset.

Fine with me.

But we need to merge something short term (pre 0.13) to fix hot plug of
e1000 et al.  Use Alex's patch as such a stop-gap?