a quetion about sysbus_realize_and_unref function

[Chan Kim]

Hi, list members,

I see for example in hw/arm/virt.c, when it creates a device to attach to a
system bus, it calls "sysbus_realize_and_unref(SYS_BUS_DEVICE(dev),
&error_fatal);" function

.

static void create_its(VirtMachineState *vms)

{

    const char *itsclass = its_class_name();

    DeviceState *dev;

 

    if (!itsclass) {

        /* Do nothing if not supported */

        return;

    }

 

    dev = qdev_new(itsclass);

 

    object_property_set_link(OBJECT(dev), "parent-gicv3", OBJECT(vms->gic),

                             &error_abort);

    sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);

    sysbus_mmio_map(SYS_BUS_DEVICE(dev), 0, vms->memmap[VIRT_GIC_ITS].base);

 

    fdt_add_its_gic_node(vms);

    vms->msi_controller = VIRT_MSI_CTRL_ITS;

}

 

The document says it decrements the reference counter and when the ref count
is non zero, the object can't be removed.

Then why does it call sysbus_realize_and_unref function to reduce the ref
count of the system bus(=parent object) of the device being create?

Thank you,

Chan Kim