Re: [Qemu-devel] [PATCH v9 05/10] move out net queue structs define

[Stefan Hajnoczi <stefanha@redhat.com>]

On Mon, Sep 07, 2015 at 03:37:20PM +0800, Yang Hongyang wrote:
> Hi Stefan,
> 
> On 09/04/2015 06:32 PM, Stefan Hajnoczi wrote:
> [...]
> >
> >net/queue.c has logic to send/queue/flush packets but a
> >qemu_deliver_packet() call is hardcoded.
> >
> >Maybe you can extend qemu_new_net_queue() like this:
> >
> >/* Returns:
> >  *   >0 - success
> >  *    0 - queue packet for future redelivery
> >  *   <0 - failure (discard packet)
> >  */
> >typedef ssize_t NetQueueDeliverFunc(NetClientState *sender,
> >                                     unsigned flags,
> >				    const struct iovec *iov,
> >				    int iovcnt,
> >				    void *opaque);
> >
> >NetQueue *qemu_new_net_queue(NetQueueDeliverFunc deliver,
> >                              void *opaque);
> >
> >Now net/net.c:qemu_net_client_setup() needs to call:
> >
> >   nc->incoming_queue = qemu_new_net_queue(qemu_deliver_packet_iov, nc);
> >
> >And the filter code can use qemu_net_queue_send_iov() and
> >qemu_net_queue_flush().  The filter just needs to provide its own
> >NetQueueDeliveryFunc.
> >
> >I haven't checked the details (e.g. non-iov delivery, etc) but the idea
> >is to use the net/queue.c API instead of duplicating similar logic in
> >the filter code.
> 
> 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.

Stefan