Re: [Qemu-devel] [PATCH v1 RFC 04/34] qom: add object_new_propv / object_new_proplist constructors

[Eric Blake]

On 04/17/2015 08:22 AM, Daniel P. Berrange wrote:
> It is reasonably common to want to create an object, set a
> number of properties, register it in the hierarchy and then
> mark it as complete (if a user creatable type). This requires
> quite alot of error prone, verbose, boilerplate code to achieve.

s/alot/a lot/

> 
> The object_new_propv / object_new_proplist constructors will
> simplify this task by performing all required steps in one go,
> accepting the property names/values as variadic args.
> 
> Usage would be:
> 
>    Error *err = NULL;
>    Object *obj;
>    obj = object_new_propv(TYPE_MEMORY_BACKEND_FILE,
>                           "hostmem0",
>                           &err,
>                           "share", "yes",
>                           "mem-path", "/dev/shm/somefile",
>                           "prealloc", "yes",
>                           "size": "1048576",

s/:/,/

>                           NULL);
> 
> Note all property values are passed in string form and will
> be parsed into their required data types.
> 
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
>  include/qom/object.h | 58 +++++++++++++++++++++++++++++++++++++++++++++++
>  qom/object.c         | 64 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/Makefile       |  2 +-
>  3 files changed, 123 insertions(+), 1 deletion(-)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index d2d7748..223b577 100644
> --- a/include/qom/object.h

> + *
> + *   obj = object_new_propv(TYPE_MEMORY_BACKEND_FILE,
> + *                          "hostmem0",
> + *                          &err,
> + *                          "share", "yes",
> + *                          "mem-path", "/dev/shm/somefile",
> + *                          "prealloc", "yes",
> + *                          "size": "1048576",

and again

> + *                          NULL);
> + *
> + *   if (!obj) {
> + *     g_printerr("Cannot create memory backend: %s\n",
> + *                error_get_pretty(err));
> + *   }
> + *
> + * Returns: The newly allocated, instantiated & initialized object.
> + */
> +Object *object_new_propv(const char *typename,
> +                         const char *id,
> +                         Error **errp,
> +                         ...);

You probably want to use the gcc __attribute__((__sentinel__)), so that
the compiler can ensure that the caller NULL-terminates their list.


> +Object *object_new_proplist(const char *typename,
> +                            const char *id,
> +                            Error **errp,
> +                            va_list vargs)
> +{
> +    Object *obj;
> +    const char *propname;
> +
> +    obj = object_new(typename);
> +
> +    if (object_class_is_abstract(object_get_class(obj))) {
> +        error_setg(errp, "object type '%s' is abstract", typename);
> +        goto error;
> +    }
> +
> +    propname = va_arg(vargs, char *);
> +    while (propname != NULL) {
> +        const char *value = va_arg(vargs, char *);
> +
> +        object_property_parse(obj, value, propname, errp);

Is it worth a sanity check of assert(value) prior to calling
object_property_parse(), as I have the suspicion that it doesn't handle
NULL very well?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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