[Qemu-devel] Re: make qdev to use already assigned memory

[Juan Quintela <quintela@redhat.com>]

Gerd Hoffmann <kraxel@redhat.com> wrote:
>   Hi,
>
>> DeviceState *qdev_create_here(DeviceState *dev, BusState *bus, const char *name)
>>
>> The only change is that it don't want qemu_malloc(), it just initialize
>> the device in the memory that I bring there.  Why do I want this?
>
> I'd prefer to not have such a function.
>
> At the end of the qdev conversion we want to have all drivers in a
> state where you can create the devices using the basic sequence ...
>
>   (1) qdev_create()
>   (2) setting properties
>   (2) qdev_init()
>
> ... from generic code.  qdev_create_here() simply doesn't fit in
> here. It can by definition not be called by generic code.  Only a very
> few special cases could actually make use of it.
>
> It would make alot of sense to allow *bus* data structures being
> embedded though.  A bus is never ever created on its own, it is
> allways created by the parent device (lsi creates a scsi bus, ...).
> Would that solve your problems?

At least it is a big step in the right direction :)
I think we would have to set with this one for now.  If I found any
other pattern, would let you know.

> I think that one can also be solved by splitting pci bus registration
> and pci bus irq setup into two functions.

It will fix this one.

>> hw/fdc.c
>
>> struct fdctrl_t {
>>      /* Command FIFO */ /* 1st field */
>>      uint8_t fifo[512];
>>      ....
>> };
>
>> And now I will call qemu_memalign() for the whole structure.
>
> Doesn't fly.  isa-fdc is pretty close to the state where it can be
> created via -device, we just need the drive windup.  When creating the
> floppy controller via '-device isa-fdc,driveA=foo,driveB=bar' or
> simliar, who will call qemu_memalign then?  Also note that DeviceState
> must be at offset zero of the device state struct.

I know this one in borderline (to say the less), but I was just putting
the examples where i needed them in the last two days.  I.e. that they
weren't "theoretical" problems.

Thanks, Juan.