From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:52084)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <imammedo@redhat.com>) id 1VlgFx-00017l-7C
	for qemu-devel@nongnu.org; Wed, 27 Nov 2013 09:38:27 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <imammedo@redhat.com>) id 1VlgFr-0004W4-7r
	for qemu-devel@nongnu.org; Wed, 27 Nov 2013 09:38:21 -0500
Received: from mx1.redhat.com ([209.132.183.28]:49827)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <imammedo@redhat.com>) id 1VlgFr-0004Vz-06
	for qemu-devel@nongnu.org; Wed, 27 Nov 2013 09:38:15 -0500
Date: Wed, 27 Nov 2013 15:37:52 +0100
From: Igor Mammedov <imammedo@redhat.com>
Message-ID: <20131127153752.2d5d7220@nial.usersys.redhat.com>
In-Reply-To: <52937641.30003@redhat.com>
References: <1385001528-12003-1-git-send-email-imammedo@redhat.com>
	<1385001528-12003-8-git-send-email-imammedo@redhat.com>
	<52934872.60904@redhat.com>
	<20131125170158.1258f535@nial.usersys.redhat.com>
	<52937641.30003@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 07/27] add memdev backend infrastructure
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: peter.maydell@linaro.org, mdroth@linux.vnet.ibm.com, mst@redhat.com, mjt@tls.msk.ru, stefanb@linux.vnet.ibm.com, stefanha@redhat.com, armbru@redhat.com, qemu-devel@nongnu.org, vasilis.liaskovitis@profitbricks.com, quintela@redhat.com, chegu_vinod@hp.com, kraxel@redhat.com, aliguori@amazon.com, hutao@cn.fujitsu.com, marcel.a@redhat.com, lcapitulino@redhat.com, afaerber@suse.de

On Mon, 25 Nov 2013 17:09:37 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:

> Il 25/11/2013 17:01, Igor Mammedov ha scritto:
> >> > So this is why you need a new command-line option.
> >> > 
> >> > I think we need a generic mechanism for post-initialization of whatever
> >> > is given on the command line.  Perhaps you can do that with an
> >> > interface, and get rid of -memdev and memdev_add altogether?
> >> > 
> >> > MemoryBackend's implementation of the interface's sole method would call
> >> > get_memory, of course.
> > 
> > What I would use instead of memdev_add in CLI/HMP/QMP?
> 
> We could add a new object_add command.
> 
> > Could you explain it a bit more, please?
> 
> The interface would look like
> 
> struct QOMCommandLineIface {
>     void complete(Object *object, Error **errp);
>     Object *get_base_path(void);
> }
> 
> MemoryBackend could implement it like this:
> 
> void memory_backend_complete(Object *object, Error **errp)
> {
>     MemoryBackend *backend = MEMORY_BACKEND(object);
>     MemoryBackendClass *bc = MEMORY_BACKEND_GET_CLASS(obj);
>     if (bc->get_memory) {
>         bc->get_memory(backend, errp);
>     }
> }
> 
> Object *memory_backend_get_base_path(void);
> {
>     return container_get(qdev_get_backend(), "/memdev"),
> }
> 
> A default implementation can be added to RNGBackend and TPMBackend.
> vl.c can use the interface like this in object_create:
> 
>     obj = object_new(type);
>     QOMCommandLineIface *cmdline_iface;
> 
>     if (IS_QOM_COMMAND_LINE(obj)) {
>         object_unref(obj);
>         error...
>         return -1;
>     }
> 
>     if (qemu_opt_foreach(opts, object_set_property, obj, 1) < 0) {
>         object_unref(obj);
>         return -1;
>     }
> 
>     cmdline_iface = QOM_COMMAND_LINE_GET_IFACE(obj);
>     cmdline_iface->complete(obj, &local_err);
>     if (local_err)) {
>         error_propagate(...)
>         object_unref(obj);
>         return -1;
>     }
> 
>     object_property_add_child(cmdline_iface->get_base_path(),
>                               id, obj, NULL);
> 
> Then you can just use -object instead of -memdev.
It looks like "realize" for -object / object-add implemented via
an interface.

Maybe it should be renamed from QOMCommandLineIface to QOMRealizeIface
and s/complete/realize/ so anyone who knows about Device.realize would
get meaning without digging in complete() implementations.

Alternative would be to behave just like Rng/Tpm do, i.e. use -object
to do late initialization in a backend user (DimmDevice.realize).
Draw back of it would be user won't get error during the first command
"object-add" and only will get error when creating DimmDevice calling
"device_add".