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Date: Mon, 25 Nov 2013 17:09:37 +0100
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Subject: Re: [Qemu-devel] [PATCH 07/27] add memdev backend infrastructure
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To: Igor Mammedov <imammedo@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

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.