Re: [Qemu-devel] [PATCH] i2c: factor out VMSD to parent class

[Peter Maydell]

On 14 August 2012 09:27, Juan Quintela <address@hidden> wrote:
> "Peter A. G. Crosthwaite" <address@hidden> wrote:
>> Hi All. PMM raised a query on a recent series of mine (the SSI series) about
>> handling VMSD for devices which define state at multiple levels of the QOM
>> heirachy.

> - If you ask me, I would very much preffer something like PCI devices,
>   where the 1st field of any specific device is the i2c part.  This
>   would achieve two things:
>    * all i2c devices would have the common fields at the beggining
>    * we sent the data for one device in one go, so we will never had
>      trouble making sure that both devices arrive at the same time, in
>      the right order, etc.
>
> - I guess there is same reasy why you want to split the device state,
>   it could be on the other series where I haven't read it though.

Really I'm just trying to get clarification on how class hierarchies should
handle vmstate. At the moment any device which is a subclass of i2c
has a VMSTATE_I2C_SLAVE field corresponding to the element in
its struct which is its parent object. This seems a bit odd because
surely the parent class should be responsible for its own save/load?
I'm also not sure we do this consistently through the whole QOM
hierarchy.

So what I'm after is not necessarily a patch so much as a decision about
which way this should be handled. This would probably be good to put
in a section of Anthony's QOM style guide...

-- PMM