Re: [Qemu-devel] [PATCH 14/18] rtc: add a dynamic property for retrieving the date

[Anthony Liguori]

On 12/01/2011 09:46 AM, Gerd Hoffmann wrote:
>    Hi,
>
> > +static void rtc_get_date(DeviceState *dev, Visitor *v, void *opaque,
> > +                         const char *name, Error **errp)
> > +{
> > +    ISADevice *isa = DO_UPCAST(ISADevice, qdev, dev);
> > +    RTCState *s = DO_UPCAST(RTCState, dev, isa);
> > +
> > +    visit_start_struct(v, NULL, "struct tm", name, 0, errp);
> > +    visit_type_int32(v,&s->current_tm.tm_year, "tm_year", errp);
> > +    visit_type_int32(v,&s->current_tm.tm_mon, "tm_mon", errp);
> > +    visit_type_int32(v,&s->current_tm.tm_mday, "tm_mday", errp);
> > +    visit_type_int32(v,&s->current_tm.tm_hour, "tm_hour", errp);
> > +    visit_type_int32(v,&s->current_tm.tm_min, "tm_min", errp);
> > +    visit_type_int32(v,&s->current_tm.tm_sec, "tm_sec", errp);
> > +    visit_end_struct(v, errp);
> > +}
>
> Ok, what is the long term plan here?  I don't think we want open-code
> everything here, do we?  Especially once visitors become more widespread
> used.  And I can see that they are useful for a bunch of stuff beside
> device properties and relationships.  vmstate for example.  Or to list
> device state (say a register dump) for debugging purposes.
>
> Today we have code to generate structs and visitors from scratch.
> I think it would be useful to also generate visitors for existing
> structs, with some kind of annotation, like this ...
>
> struct SomeDev {
>        DeviceState dev;
>        Chardev     *chr;
>        uint32_t    reg1   __v(vmstate);
>        uint32_t    reg2   __v(vmstate);
>        [ ... ]
> );

https://github.com/aliguori/qidl/

In your example:

struct SomeDev {
       DeviceState _immutable dev;
       Chardev _immutable     *chr;
       uint32_t               reg1;
       uint32_t               reg2;
       [ ... ]
};

> ... instead of the vmstate structs we create manually today.  Likewise
> for properties.  And probably we can even generate different visitors
> for different "views" at the same struct.

qc generates a json description of the struct.  You can then use a generate to 
take that json and generate code for VMState, QAPI, etc.

The readme has quite a lot of detail about the syntax.  The parser is pretty 
complete already.

https://github.com/aliguori/qidl/blob/master/qc.md

But I want to get us moving on QOM first before I go any further with this.  We 
can always go back and remove the manually written visit functions.

Regards,

Anthony Liguori

> cheers,
>    Gerd