Re: [Qemu-devel] [PATCH] qom: helper macro for adding read-only properties

["Andreas Färber" <afaerber@suse.de>]

Am 15.09.2013 19:23, schrieb Michael S. Tsirkin:
> Add a helper macro for adding read-only properties, that works in the
> common case where the value is a constant.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> I'm using this patch in my acpi work - any objections
> to applying it on my tree?

Actually yes: Apart from the clang issues raised and the disturbing
upper-casing of arguments, this is hardcoding "int" type and NULL errp,
so I don't think it deserves to live in object.h as is. I do agree that
we could use more helper functions to deal with dynamic properties.

So what about taking bool/string property helpers as example and putting
intX_t getters into object.c, using a passed-through opaque argument to
obtain the value? We could then have real object_property_add_int32()
etc. functions using the appropriate type name, with field/value pointer
and Error** arguments. A pointer can be assumed to hold up to uint32_t
values or, to keep the API more general, use a local static const
variable for non-field values.

It does touch on the issue I brought up on a KVM call a couple weeks ago
of how dynamic and static properties are supposed to relate. I
personally welcome making dynamic properties more easy to deal with; an
alternative might be to extend qdev-properties.c with
DEFINE_PROP_READONLY_UINT32() etc. CC'ing Igor, who has dealt with
dynamic-vs.-static properties for X86CPU.

Regards,
Andreas

> 
>  include/qom/object.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index 1a7b71a..4787de6 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -17,6 +17,7 @@
>  #include <glib.h>
>  #include <stdint.h>
>  #include <stdbool.h>
> +#include "qemu/typedefs.h"
>  #include "qemu/queue.h"
>  
>  struct Visitor;
> @@ -792,6 +793,26 @@ void object_property_add(Object *obj, const char *name, const char *type,
>                           ObjectPropertyRelease *release,
>                           void *opaque, struct Error **errp);
>  
> +/* Add a property that is an integer constant. */
> +#define OBJECT_ADD_PROP_CONST(obj, name, value)                      \
> +    do {                                                                    \
> +        void OBJECT_ADD_PROP_GET(Object *OBJECT_ADD_PROP_OBJ,               \
> +                                 struct Visitor *OBJECT_ADD_PROP_VISITOR,   \
> +                                 void *OBJECT_ADD_PROP_OPAQUE,              \
> +                                 const char *OBJECT_ADD_PROP_NAME,          \
> +                                 struct Error **OBJECT_ADD_PROP_VALUE_ERR)  \
> +        {                                                                   \
> +            int64_t OBJECT_ADD_PROP_VALUE = value;                          \
> +                                                                            \
> +            visit_type_int64(OBJECT_ADD_PROP_VISITOR,                       \
> +                             &OBJECT_ADD_PROP_VALUE,                        \
> +                             OBJECT_ADD_PROP_NAME,                          \
> +                             OBJECT_ADD_PROP_VALUE_ERR);                    \
> +        }                                                                   \
> +        object_property_add(obj, name, "int", OBJECT_ADD_PROP_GET,          \
> +                            NULL, NULL, NULL, NULL);                        \
> +    } while (0)
> +
>  void object_property_del(Object *obj, const char *name, struct Error **errp);
>  
>  /**
> 


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