Re: [Qemu-devel] [PATCH] qdev: The sequence of devices added to bus

[Paolo Bonzini <pbonzini@redhat.com>]

On 19/01/2015 08:01, Ting Wang wrote:
> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> index 901f289..7d830a6 100644
> --- a/hw/core/qdev.c
> +++ b/hw/core/qdev.c
> @@ -89,7 +89,7 @@ static void bus_add_child(BusState *bus, DeviceState *child)
>      kid->child = child;
>      object_ref(OBJECT(kid->child));
>  
> -    QTAILQ_INSERT_HEAD(&bus->children, kid, sibling);
> +    QTAILQ_INSERT_TAIL(&bus->children, kid, sibling);
>  
>      /* This transfers ownership of kid->child to the property.  */
>      snprintf(name, sizeof(name), "child[%d]", kid->index);
> 

Hi Ting,

I think this patch had already been submitted in the past.

The result of the discussion was that:

1) the behavior you report was not reproduced consistently.  This means
that it is either a race condition, or it depends on the kernel release.
 In fact I think a race condition here is expected, and thus the patch
wouldn't entirely fix the problem.

2) This would be a change in the guest interface, so it is unfortunately
too late to do it unconditionally.  You could do it only for new machine
types, but it would be a very intrusive change with very high
probability of breaking something---much more than anything else we do
for new machine types.  So it is probably not a good idea.

Paolo