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

[Gerd Hoffmann <kraxel@redhat.com>]

   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?

>      PIIX3IrqState *irq_state = qemu_malloc(sizeof(*irq_state));
>
>      irq_state->pic = pic;
>      dev = qdev_create(NULL, "i440FX-pcihost");
>      s = FROM_SYSBUS(I440FXState, sysbus_from_qdev(dev));
>      b = pci_register_bus(&s->busdev.qdev, "pci.0",
>                           piix3_set_irq, pci_slot_get_pirq, irq_state, 0, 4);
>      s->bus = b;
>      qdev_init(dev);
>
>      d = pci_create_simple(b, 0, "i440FX");
>      *pi440fx_state = DO_UPCAST(PCII440FXState, dev, d);
>      (*pi440fx_state)->irq_state = irq_state;

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

> 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.

cheers,
   Gerd