Re: Purpose of QOM properties registered at realize time?

[Paolo Bonzini]

On 07/10/20 00:06, Eduardo Habkost wrote:
> Hi,
> 
> While trying to understand how QOM properties are used in QEMU, I
> stumbled upon multiple cases where alias properties are added at
> realize time.
> 
> Now, I don't understand why those properties exist.  As the
> properties are added at realize time, I assume they aren't
> supposed to be touched by the user at all.  If they are not
> supposed to be touched by the user, what exactly is the purpose
> of those QOM properties?

In the case of GPIOs, I think they will be used by other devices that
are added afterwards.

The remaining ones are:

> hw/arm/allwinner-h3.c=232=static void allwinner_h3_realize(DeviceState *dev, 
> Error **errp)
> hw/arm/allwinner-h3.c:359:    object_property_add_alias(OBJECT(s), "sd-bus", 
> OBJECT(&s->mmc0),
> --
> hw/arm/bcm2835_peripherals.c=128=static void 
> bcm2835_peripherals_realize(DeviceState *dev, Error **errp)
> hw/arm/bcm2835_peripherals.c:322:    object_property_add_alias(OBJECT(s), 
> "sd-bus", OBJECT(&s->gpio), "sd-bus");
> --
> hw/arm/bcm2836.c=69=static void bcm2836_realize(DeviceState *dev, Error 
> **errp)
> hw/arm/bcm2836.c:87:    object_property_add_alias(OBJECT(s), "sd-bus", 
> OBJECT(&s->peripherals),
> --
> hw/arm/xlnx-zynqmp.c=276=static void xlnx_zynqmp_realize(DeviceState *dev, 
> Error **errp)
> hw/arm/xlnx-zynqmp.c:522:        object_property_add_alias(OBJECT(s), 
> bus_name, sdhci, "sd-bus");

And this are probably usable with "bus=sd-bus" or something like that on
other devices, too.

Paolo