Re: [Qemu-devel] KVM call minutes for Feb 8

[Anthony Liguori]

On 02/15/2011 11:11 AM, Blue Swirl wrote:
> On Mon, Feb 14, 2011 at 11:47 PM, Anthony Liguori<address@hidden>  wrote:
>    
> > Any device we expose to the user through -device needs to maintain a
> > compatible interface forever.  For our own sanity, I think we should try to
> > expose as little as possible.
> >      
> Restricting the users from adding arbitrary devices is a different
> issue. Dropping qdev support to prevent user from adding the device
> seems draconian, what's wrong with no_user flag?
>    

I think you're missing my point.

It should be possible to make a device "qdev" without exposing it via a 
factory interface.  Today it's all or nothing and that's the part I dislike.

no_user is a hack.  We can do better.

> > A good example of a device that we should model through qdev but not expose
> > via -device is actually SerialState.
> >      
> You wouldn't want users to add any serial ports? What should be do
> with serial ports then, always enable a full set of ports? How would
> the user use them?
>    

No, users should be able to create ISASerialDevice, MMIOSerialDevice, 
but not UART16650A.  Here's what I'm talking about:

class ISASerialDevice : public ISADevice
{
    UART16650A uart;
};

class MMIOSerialDevice : public PlatformDevice
{
    UART16650A uart;
};

There should be factory interfaces for ISASeriaDevice and 
MMIOSerialDevice but not UART16650A.

> > Today, we have ISASerialState which embeds SerialState.  We can also create
> > a MMIO version of SerialState although there's no direct structure that
> > wraps that.
> >
> > Ideally, SerialState would be a proper qdev device that is embedded in both
> > ISASerialState and MMIOSerialState (or pick a better name).  info qtree
> > should show a has-a relationship for these devices.
> >      
> I think the devices shown in qtree should always have some
> relationship to real devices. If ICH10 contains all possible onboard
> devices, including for example HPET, e1000 and SATA, that could use a
> has-a relationship to show the composition

Yeah, I'm not disagreeing at all.

Ignoring the fact that modern uarts are implemented in a super i/o chip, 
it's same chip whether it's soldered directly on a board with direct 
connections to a CPU bus or whether it's exposed on the ISA bus.

Regards,

Anthony Liguori

>   but otherwise I fear this
> would only increase complexity with no gain.
>
>