Re: [Qemu-devel] Re: [PATCH 5/5] RFC: distinguish warm reset from cold reset.

[Anthony Liguori <anthony@codemonkey.ws>]

On 08/31/2010 08:46 AM, Avi Kivity wrote:
>  On 08/31/2010 04:34 PM, Anthony Liguori wrote:
>> On 08/31/2010 08:29 AM, Avi Kivity wrote:
>>> Note, for most devices there's no difference.  x86 has INIT and 
>>> RESET, with the keyboard controller RESET signal sometimes wired to 
>>> INIT, and RAM doesn't have RESET.  Otherwise most devices don't see 
>>> a difference.
>>
>> Yes, that's why I'm wondering if we can just get away with using a 
>> simple reset() callback and for the handful of devices that don't do 
>> a full reset, they can just move the state unaffected by warm reset 
>> to ->init().
>>
>
> This seems reasonable.

But I'm still not sure whether the reset signal can be deliver based on 
a pre-order transversal or whether a custom transversal was required 
that each bus participates in.

>> For cold reset, I'd rather approach it as a device destroy + create.  
>> This means that given a DeviceState, we need to collect enough 
>> information to recreate the device.  I'm not 100% sure we have that 
>> today but if we solve that problem, it means we can migrate the 
>> device tree during migration which is a feature I'd really like to see.
>
> Why do we need a cold reset at all?  it doesn't map to anything.

That's why I'm suggesting a second-class approach to implementing it if 
someone really wants it.

Regards,

Anthony Liguori