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

Anthony Liguori
2011-02-15T23:07:25Z

On 02/15/2011 11:11 AM, Blue Swirl wrote:
> On Mon, Feb 14, 2011 at 11:47 PM, Anthony Liguori<anthony@codemonkey.ws> 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.
>
>