Re: [Qemu-devel] [PATCH 2/7] iohandlers: Introduce a new API

[Anthony Liguori]

On 02/22/2011 10:21 AM, Avi Kivity wrote:
> On 02/22/2011 05:00 PM, Anthony Liguori wrote:
> > > Drop the opaque, instead put the IOHandler in there (or maybe the 
> > > CharDev?) and use container_of().
> >
> >
> > You know, I'm not there that this is automatically better.
>
> Why not?  One less unsafe cast.

It turns out there are a lot of cases in QEMU where there isn't an 
obvious data structure to piggy back on.

> > Why is there an IOHandler and an IOEventHandler argument for init?

So wouldn't you set the IOEventHandler directly in the IOHandler as part 
of initialization?  IOW:

struct MyDevice {
    IOHandler iohandler;
};

iohandler.func = my_io_function;
io_handler_init(&iohandler, fd, event_mask);

That's the paradigm I'm used to at least.

Regards,

Anthony Liguori

> IOHandler is the object, IOEventHandler is the function call.
>
> Basically this is a 1:1 translation of
>
> class IOHandler {
> public:
>     IOHandler(int fd, unsigned mask);
>     ~IOHandler();
>     virtual void io_event_handler() = 0;
>     unsigned event_mask();
>     void set_event_mask(unsigned mask);
> }
>
> class MyClient : private IOHandler {
>     virtual void io_event_handler();
> }
>
> where the compiler automatically generates the container_of() to get 
> to the actual MyClient pointer.