Re: [Qemu-devel] [RFC PATCH qemu] qmp: Add qom-list-properties to list QOM object properties

[Markus Armbruster]

Alexey Kardashevskiy <address@hidden> writes:

> There is already 'device-list-properties' which does most of the job,
> however it does not handle everything returned by qom-list-types such
> as machines as they inherit directly from TYPE_OBJECT and not TYPE_DEVICE.
>
> This adds a new qom-list-properties command which prints properties
> of a specific class and its instance. It is pretty much a simplified copy
> of the device-list-properties handler.
>
> Since it creates an object instance, device properties should appear
> in the output as they are copied to QOM properties at the instance_init
> hook.
>
> Signed-off-by: Alexey Kardashevskiy <address@hidden>

Related: qom-list, which lists "any properties of a object given a path
in the object model."  qom-list-properties takes a type name, which
qom-list takes the path to an instance.  In other words,
qom-list-properties is like instantiate with default configuration and
without realizing + qom-list + destroy.

We need to instantiate because QOM properties are dynamic: they aren't
specified by data (which qom-list-properties could simply read), they
are created by (instantiation) code (which qom-list-properties has to
run).

Properties created only after instantiation (by realize, perhaps) aren't
visible in qom-list-properties.  Do such properties exist?

Properties created only in non-default configuration aren't visible
either.  Such properties have to exist, or else dynamic property
creation would be idiotic.

Likewise for properties created differently (say with a different type)
in non-default configuration.  We can hope that no such beasts exist.
Since properties get created by code, and code can do anything, we're
reduced to hope.  Data is so much easier to reason about than code.

Three building blocks: instantiate, qom-list, destroy.  Do we want the
building blocks, or do we want their combination qom-list-properties?

> ---
>
> I am missing the point of make_device_property_info().
> qmp_device_list_properties() creates the instance which copies everything
> to QOM properties hashtable and commenting out the do{}while() in
> make_device_property_info() does not seem to change a thing, what case
> am I missing here?

git-blame points to Stefan.  Stefan, can you help?

> ---
>  qapi-schema.json | 29 +++++++++++++++++++++++++++++
>  qmp.c            | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 81 insertions(+)
>
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 5c06745..9d73501 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1455,6 +1455,35 @@
>    'returns': [ 'DevicePropertyInfo' ] }
>  
>  ##
> +# @QOMPropertyInfo:
> +#
> +# Information about object properties.
> +#
> +# @name: the name of the property
> +# @type: the typename of the property
> +# @description: if specified, the description of the property.
> +#
> +# Since: 2.12
> +##
> +{ 'struct': 'QOMPropertyInfo',
> +  'data': { 'name': 'str', 'type': 'str', '*description': 'str' } }
> +
> +##
> +# @qom-list-properties:
> +#
> +# List properties associated with a QOM object.
> +#
> +# @typename: the type name of an object
> +#
> +# Returns: a list of QOMPropertyInfo describing object properties
> +#
> +# Since: 2.12
> +##
> +{ 'command': 'qom-list-properties',
> +  'data': { 'typename': 'str'},
> +  'returns': [ 'QOMPropertyInfo' ] }
> +
> +##
>  # @xen-set-global-dirty-log:
>  #
>  # Enable or disable the global dirty log mode.
> diff --git a/qmp.c b/qmp.c
> index 52cfd2d..20cb662 100644
> --- a/qmp.c
> +++ b/qmp.c
> @@ -574,6 +574,58 @@ DevicePropertyInfoList *qmp_device_list_properties(const 
> char *typename,
>      return prop_list;
>  }
>  
> +QOMPropertyInfoList *qmp_qom_list_properties(const char *typename,
> +                                             Error **errp)
> +{
> +    ObjectClass *klass;
> +    Object *obj;
> +    ObjectProperty *prop;
> +    ObjectPropertyIterator iter;
> +    QOMPropertyInfoList *prop_list = NULL;
> +
> +    klass = object_class_by_name(typename);
> +    if (klass == NULL) {
> +        error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
> +                  "Class '%s' not found", typename);
> +        return NULL;
> +    }
> +
> +    klass = object_class_dynamic_cast(klass, TYPE_OBJECT);
> +    if (klass == NULL) {
> +        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "typename", 
> TYPE_OBJECT);
> +        return NULL;
> +    }
> +
> +    if (object_class_is_abstract(klass)) {
> +        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "typename",
> +                   "non-abstract class");
> +        return NULL;
> +    }
> +
> +    obj = object_new(typename);
> +
> +    object_property_iter_init(&iter, obj);
> +    while ((prop = object_property_iter_next(&iter))) {
> +        QOMPropertyInfo *info;
> +        QOMPropertyInfoList *entry;
> +
> +        info = g_malloc0(sizeof(*info));
> +        info->name = g_strdup(prop->name);
> +        info->type = g_strdup(prop->type);
> +        info->has_description = !!prop->description;
> +        info->description = g_strdup(prop->description);
> +
> +        entry = g_malloc0(sizeof(*entry));
> +        entry->value = info;
> +        entry->next = prop_list;
> +        prop_list = entry;
> +    }
> +
> +    object_unref(obj);
> +
> +    return prop_list;
> +}
> +
>  CpuDefinitionInfoList *qmp_query_cpu_definitions(Error **errp)
>  {
>      return arch_query_cpu_definitions(errp);