On Mon, Sep 07, 2015 at 06:53:49PM +0800, Yang Hongyang wrote:
On 09/07/2015 05:11 PM, Stefan Hajnoczi wrote:
[...]
Thanks very much for the suggestion, I've already implemented it and tested,
the code looks cleaner now.
The last issue is the QOM thing, do Markus and Andreas have more input
about that?
If you would like to see examples of QOM usage, take a look at
iothread.c and/or backends/hostmem.c.
The key things are:
1. They use include/qom/object.h to register a type based on
TYPE_OBJECT and their properties are registered using
object_property_add_*().
2. They implement the TYPE_USER_CREATABLE interface so the -object
command-line option can be used to instantiate them. See
object_interfaces.h.
As a result, a lot of code becomes unnecessary and iothread.c, in
particular, is quite short.
After looking into this, I have some questions on the implement, could you
please help me on this because I don't know much about the object mechanism:
The netfilter need to be initialized after the net_init_clients, because we
need to attach the filter to the net client. But currently, net client is not
using QOM, and seems that it is initialized after objects been created. So here
comes the problem: how can I initialize a certain object later, is it possiable?
It is currently a bit hacky - most objects are initialized very early,
but we have a similar problem with rng-egd which must be created /after/
chardevs. To deal with this in vl.c main() we have two helper methods
object_create_initial and object_create_delayed. The delayed method though
still happens before the net clients are created. We could probably just
move the objec_create_delayed method invokation to later on, after net
clients are created, but if that doesn't work just add an extra helper
object_create_very_delayed :-)