Re: [Qemu-devel] [PATCH v2] hw/core/bus.c: Only the main system bus can have no parent

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 5/23/19 5:05 PM, Peter Maydell wrote:
> In commit 80376c3fc2c38fdd453 in 2010 we added a workaround for
> some qbus buses not being connected to qdev devices -- if the
> bus has no parent object then we register a reset function which
> resets the bus on system reset (and unregister it when the
> bus is unparented).
> 
> Nearly a decade later, we have now no buses in the tree which
> are created with non-NULL parents, so we can remove the
> workaround and instead just assert that if the bus has a NULL
> parent then it is the main system bus.
> 
> (The absence of other parentless buses was confirmed by
> code inspection of all the callsites of qbus_create() and
> qbus_create_inplace() and cross-checked by 'make check'.)
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> ---
> v1->v2: clean up also the bus_unparent() code
> ---
>  hw/core/bus.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/hw/core/bus.c b/hw/core/bus.c
> index e09843f6abe..b8839c7268d 100644
> --- a/hw/core/bus.c
> +++ b/hw/core/bus.c
> @@ -96,10 +96,9 @@ static void qbus_realize(BusState *bus, DeviceState *parent, const char *name)
>          bus->parent->num_child_bus++;
>          object_property_add_child(OBJECT(bus->parent), bus->name, OBJECT(bus), NULL);
>          object_unref(OBJECT(bus));
> -    } else if (bus != sysbus_get_default()) {
> -        /* TODO: once all bus devices are qdevified,
> -           only reset handler for main_system_bus should be registered here. */
> -        qemu_register_reset(qbus_reset_all_fn, bus);
> +    } else {
> +        /* The only bus without a parent is the main system bus */
> +        assert(bus == sysbus_get_default());
>      }
>  }
>  
> @@ -108,18 +107,16 @@ static void bus_unparent(Object *obj)
>      BusState *bus = BUS(obj);
>      BusChild *kid;
>  
> +    /* Only the main system bus has no parent, and that bus is never freed */
> +    assert(bus->parent);
> +
>      while ((kid = QTAILQ_FIRST(&bus->children)) != NULL) {
>          DeviceState *dev = kid->child;
>          object_unparent(OBJECT(dev));
>      }
> -    if (bus->parent) {
> -        QLIST_REMOVE(bus, sibling);
> -        bus->parent->num_child_bus--;
> -        bus->parent = NULL;
> -    } else {
> -        assert(bus != sysbus_get_default()); /* main_system_bus is never freed */
> -        qemu_unregister_reset(qbus_reset_all_fn, bus);
> -    }
> +    QLIST_REMOVE(bus, sibling);
> +    bus->parent->num_child_bus--;
> +    bus->parent = NULL;
>  }
>  
>  void qbus_create_inplace(void *bus, size_t size, const char *typename,
> 

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>