Re: [PATCH V2 6/8] mdev: introduce virtio device and its device ops

[Jason Wang]

On 2019/9/26 äå8:48, Tian, Kevin wrote:
> > > > +};
> > > I'm not sure how stable above ops are.
> > It's the kernel internal API, so there's no strict requirement for this.
> > We will export a version value for userspace for compatibility.
> >
> >
> > > Does it make sense if defining
> > > just two callbacks here, e.g. vq_ctrl and device_ctrl, and then let the
> > > vendor driver to handle specific ops in each category (similar to how
> > > ioctl works)?
> > My understanding is that it introduce another indirection, you still
> > need to differ from different command, and it's less flexible than
> > direct callback.
> >
> > What's the value of doing this?
> I just thought doing so may provide better compatibility to the
> parent driver. Even when new op is introduced, a parent driver
> that was developed against the old set can still be loaded in the
> new kernel. It just returns error when unrecognized ops are
> routed through vq_ctrl and device_ctrl, if the userspace doesn't
> favor the exposed version value. But if above ops set is pretty
> stable, then this comment can be ignored.


This is really good point, we should keep it stable as a real transport. 
And when there's major changes, we should advertise through version then 
we can provide a new set of functions.

Thanks


> Thanks
> Kevin