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Re: [Qemu-devel] [PATCH v3 00/20] qom: dynamic properties and compositio

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH v3 00/20] qom: dynamic properties and composition tree
Date: Fri, 16 Dec 2011 07:51:13 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110831 Lightning/1.0b2 Thunderbird/3.1.13

On 12/16/2011 06:24 AM, Paolo Bonzini wrote:
On 12/16/2011 11:36 AM, Kevin Wolf wrote:
> I think actually this is not the biggest problem. child properties are
> dynamic, and it's not a problem IMO if they are created like that.

That they are added in an init function is an indicator that they aren't
really dynamic.

That's true. However, another indicator is that anything that does not have a
struct field is also not really static. :)

So right now, child properties are all "dynamic" in this sense. This could
change when Anthony converts buses to QOM. The bus right now is embedded into
the HBA's struct, is not a pointer. This likely would change when buses are
QOM-ized, but then the bus would indeed be a 100% static child.

I think having a child property that can be NULL could be

I think Anthony convinced me this is not the case (unlike links). Even if buses
and similar objects are changed to pointers because the implementation needs
that, those pointers should never be NULL (or if they can, the child property
should not exist when they are NULL).

What I would like to get to eventually is:

struct ISASerial {
   Device parent;

   UART _child uart;
   ISABus _link *bus;

A child should be able to be part of the parent devices memory with its life cycle bound to the parents life cycle. This is why a child property shouldn't be nullable.


Anthony Liguori


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