Re: [Qemu-devel] [PATCH v2 0/7] APIC/IOAPIC cleanup

[Anthony Liguori <anthony@codemonkey.ws>]

On 08/23/2010 09:00 AM, Avi Kivity wrote:
>  On 08/23/2010 04:48 PM, Anthony Liguori wrote:
>>>> The fundamental issue is: every function (minus trivial ones) in 
>>>> the device models code should have a state reference.  That state 
>>>> reference should inherit from a DeviceState.  If this statement 
>>>> isn't true, then the device has been modelled in qdev incorrectly.
>>>>
>>>> Using this test, quite a lot of the "converted" devices are being 
>>>> modelled incorrectly.
>>>
>>> Is a "state reference" allowed to have a pointer to the state, or 
>>> reach it in some other way (for example, static storage for 
>>> singleton devices)?
>>
>>
>> No.  If this was C++, then the statement would be: device have to be 
>> implemented in terms of objects that inherit from Device.  Device is 
>> our common base object.
>
> so,
>
>     struct MyDevicestate {
>         struct DeviceState device_state;
>         bool *some_bit;
>     };
>
> bad, while
>
>     struct MyDevicestate {
>         struct DeviceState device_state;
>         bool some_bit;
>     };
>
> good?

And the next logical question is whether:

struct MyDeviceState {
    DeviceState qdev;
    OtherState *s;
};

Is bad?  The answer would depend on whether OtherState implemented 
methods or not.  If OtherState has no methods, it's fine.  If it has 
methods, it's bad.

>
>
>>
>>> Isn't "save/restore works" an equivalent statement to "device state 
>>> is reachable from the DeviceState"?
>>
>> I'm not sure I can connect the dots here as I'm not sure what follows 
>> if your assertion is true.
>
> If save/restore works then all state is reachable from one point?  
> Presumable DeviceState?
>
> I really don't see why the state has to be in the DeviceState 
> subclass.  We're probably talking past each other here due to some 
> confusion in terms.

Probably.  Let's say that 'structs' are containers of primatives that 
have no methods associated with them.  'objects' are structs that have 
methods and potentially constructors/destructors.

Devices can contain references to structs and objects.  If a Device 
contains a reference to an object, the object should be stored in a 
BusState which is a container of Devices.  Therefore, the object should 
inherit from Device.

Regards,

Anthony Liguori