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

[Anthony Liguori <anthony@codemonkey.ws>]

On 08/20/2010 10:47 AM, Markus Armbruster wrote:
> Alex Williamson<alex.williamson@redhat.com>  writes:
>
>    
>> On Fri, 2010-08-20 at 11:00 +0200, Markus Armbruster wrote:
>>      
>>> Alex Williamson<alex.williamson@redhat.com>  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<alex.williamson@redhat.com>
>>>> ---
>>>>
>>>>   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.

Regards,

Anthony Liguori