Re: [PATCH v3 22/30] qom: Factor out user_creatable_process_cmdline()

[Markus Armbruster <armbru@redhat.com>]

Kevin Wolf <kwolf@redhat.com> writes:

> The implementation for --object can be shared between
> qemu-storage-daemon and other binaries, so move it into a function in
> qom/object_interfaces.c that is accessible from everywhere.
>
> This also requires moving the implementation of qmp_object_add() into a
> new user_creatable_add_qapi(), because qom/qom-qmp-cmds.c is not linked
> for tools.
>
> user_creatable_print_help_from_qdict() can become static now.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Acked-by: Peter Krempa <pkrempa@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>  include/qom/object_interfaces.h      | 41 +++++++++++++++--------
>  qom/object_interfaces.c              | 50 +++++++++++++++++++++++++++-
>  qom/qom-qmp-cmds.c                   | 20 +----------
>  storage-daemon/qemu-storage-daemon.c | 24 ++-----------
>  4 files changed, 80 insertions(+), 55 deletions(-)
>
> diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> index 5299603f50..1e6c51b541 100644
> --- a/include/qom/object_interfaces.h
> +++ b/include/qom/object_interfaces.h
> @@ -2,6 +2,7 @@
>  #define OBJECT_INTERFACES_H
>  
>  #include "qom/object.h"
> +#include "qapi/qapi-types-qom.h"
>  #include "qapi/visitor.h"
>  
>  #define TYPE_USER_CREATABLE "user-creatable"
> @@ -86,6 +87,18 @@ Object *user_creatable_add_type(const char *type, const char *id,
>                                  const QDict *qdict,
>                                  Visitor *v, Error **errp);
>  
> +/**
> + * user_creatable_add_qapi:
> + * @options: the object definition
> + * @errp: if an error occurs, a pointer to an area to store the error
> + *
> + * Create an instance of the user creatable object according to the
> + * options passed in @opts as described in the QAPI schema documentation.
> + *
> + * Returns: the newly created object or NULL on error
> + */
> +void user_creatable_add_qapi(ObjectOptions *options, Error **errp);
> +
>  /**
>   * user_creatable_add_opts:
>   * @opts: the object definition
> @@ -131,6 +144,21 @@ typedef bool (*user_creatable_add_opts_predicate)(const char *type);
>  int user_creatable_add_opts_foreach(void *opaque,
>                                      QemuOpts *opts, Error **errp);
>  
> +/**
> + * user_creatable_process_cmdline:
> + * @optarg: the object definition string as passed on the command line
> + *
> + * Create an instance of the user creatable object by parsing optarg
> + * with a keyval parser and implicit key 'qom-type', converting the
> + * result to ObjectOptions and calling into qmp_object_add().
> + *
> + * If a help option is given, print help instead and exit.
> + *
> + * This function is only meant to be called during command line parsing.
> + * It exits the process on failure or after printing help.
> + */
> +void user_creatable_process_cmdline(const char *optarg);
> +
>  /**
>   * user_creatable_print_help:
>   * @type: the QOM type to be added
> @@ -145,19 +173,6 @@ int user_creatable_add_opts_foreach(void *opaque,
>   */
>  bool user_creatable_print_help(const char *type, QemuOpts *opts);
>  
> -/**
> - * user_creatable_print_help_from_qdict:
> - * @args: options to create
> - *
> - * Prints help considering the other options given in @args (if "qom-type" is
> - * given and valid, print properties for the type, otherwise print valid types)
> - *
> - * In contrast to user_creatable_print_help(), this function can't return that
> - * no help was requested. It should only be called if we know that help is
> - * requested and it will always print some help.
> - */
> -void user_creatable_print_help_from_qdict(QDict *args);
> -
>  /**
>   * user_creatable_del:
>   * @id: the unique ID for the object
> diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> index 02c3934329..2eaf9971f5 100644
> --- a/qom/object_interfaces.c
> +++ b/qom/object_interfaces.c
> @@ -2,10 +2,13 @@
>  
>  #include "qemu/cutils.h"
>  #include "qapi/error.h"
> +#include "qapi/qapi-commands-qom.h"
> +#include "qapi/qapi-visit-qom.h"
>  #include "qapi/qmp/qdict.h"
>  #include "qapi/qmp/qerror.h"
>  #include "qapi/qmp/qjson.h"
>  #include "qapi/qobject-input-visitor.h"
> +#include "qapi/qobject-output-visitor.h"
>  #include "qom/object_interfaces.h"
>  #include "qemu/help_option.h"
>  #include "qemu/id.h"
> @@ -113,6 +116,29 @@ out:
>      return obj;
>  }
>  
> +void user_creatable_add_qapi(ObjectOptions *options, Error **errp)
> +{
> +    Visitor *v;
> +    QObject *qobj;
> +    QDict *props;
> +    Object *obj;
> +
> +    v = qobject_output_visitor_new(&qobj);
> +    visit_type_ObjectOptions(v, NULL, &options, &error_abort);
> +    visit_complete(v, &qobj);
> +    visit_free(v);
> +
> +    props = qobject_to(QDict, qobj);
> +    qdict_del(props, "qom-type");
> +    qdict_del(props, "id");
> +
> +    v = qobject_input_visitor_new(QOBJECT(props));
> +    obj = user_creatable_add_type(ObjectType_str(options->qom_type),
> +                                  options->id, props, v, errp);
> +    object_unref(obj);
> +    visit_free(v);
> +}
> +

Observation, not objection:

1. QMP core parses JSON text into QObject, passes to generated
   marshaller.

2. Marshaller converts QObject to ObjectOptions with the QObject input
   visitor, passes to qmp_object_add().

3. qmp_object_add() wraps around user_creatable_add_qapi().

4. user_creatable_add_qapi() converts right back to QObject with the
   QObject output visitor.  It splits the result into qom_type, id and
   the rest, and passes all three to user_creatable_add_type().

5. user_creatable_add_type() performs a virtual visit with the QObject
   input visitor.  The outermost object it visits itself, its children
   it visits by calling object_property_set().

I sure hope we wouldn't write it this way from scratch :)

I think your patch is a reasonable step towards a QOM that is at peace
with QAPI.  But there's plenty of work left.

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