Re: [Qemu-devel] [PATCH v2 4/7] qdev: Introduce DEFINE_PROP_LINK

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 29 Jun 2017 16:04:49 +0800
Fam Zheng <famz@redhat.com> wrote:

> This property can be used to replace the object_property_add_link in
> device code, to add a link to other objects, which is a common pattern.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  hw/core/qdev-properties.c    | 16 ++++++++++++++++
>  include/hw/qdev-core.h       |  5 +++++
>  include/hw/qdev-properties.h | 11 +++++++++++
>  3 files changed, 32 insertions(+)
> 
> diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
> index 68cd653..7c11eb8 100644
> --- a/hw/core/qdev-properties.c
> +++ b/hw/core/qdev-properties.c
> @@ -1192,3 +1192,19 @@ PropertyInfo qdev_prop_size = {
>      .set = set_size,
>      .set_default_value = set_default_value_uint,
>  };
> +
> +/* --- object link property --- */
> +
> +static void create_link_property(Object *obj, Property *prop, Error **errp)
> +{
> +    Object **child = qdev_get_prop_ptr(DEVICE(obj), prop);
> +
> +    object_property_add_link(obj, prop->name, prop->link_type,
> +                             child, prop->link.check,
> +                             prop->link.flags, errp);
> +}
> +
> +PropertyInfo qdev_prop_link = {
> +    .name = "link",
> +    .create = create_link_property,
> +};
> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> index 33518ee..40afb3d 100644
> --- a/include/hw/qdev-core.h
> +++ b/include/hw/qdev-core.h
> @@ -5,6 +5,7 @@
>  #include "qemu/option.h"
>  #include "qemu/bitmap.h"
>  #include "qom/object.h"
> +#include "qom/link-property.h"
>  #include "hw/irq.h"
>  #include "hw/hotplug.h"
>  
> @@ -233,6 +234,10 @@ struct Property {
>      int          arrayoffset;
>      PropertyInfo *arrayinfo;
>      int          arrayfieldsize;
> +    /* Only @check and @flags are used; @child is unuseful because we need a
> +     * dynamic pointer in @obj as derived from @offset. */
 @check, @flags, @child, @obj are not fields of struct Property so it's
not clear what doc comments talks about. Maybe adding prefixes would help,
for example:
  @link.child

> +    LinkProperty link;
> +    const char   *link_type;
>  };
>  
>  struct PropertyInfo {
> diff --git a/include/hw/qdev-properties.h b/include/hw/qdev-properties.h
> index 39bf4b2..767c10b 100644
> --- a/include/hw/qdev-properties.h
> +++ b/include/hw/qdev-properties.h
> @@ -30,6 +30,7 @@ extern PropertyInfo qdev_prop_pci_devfn;
>  extern PropertyInfo qdev_prop_blocksize;
>  extern PropertyInfo qdev_prop_pci_host_devaddr;
>  extern PropertyInfo qdev_prop_arraylen;
> +extern PropertyInfo qdev_prop_link;
>  
>  #define DEFINE_PROP(_name, _state, _field, _prop, _type) { \
>          .name      = (_name),                                    \
> @@ -117,6 +118,16 @@ extern PropertyInfo qdev_prop_arraylen;
>          .arrayoffset = offsetof(_state, _arrayfield),                   \
>          }
>  
> +#define DEFINE_PROP_LINK(_name, _state, _field, _type, _check, _flags) {\
> +        .name = (_name),                                                \
> +        .info = &(qdev_prop_link),                                      \
> +        .offset = offsetof(_state, _field)                              \
> +            + type_check(Object *, typeof_field(_state, _field)),       \
> +        .link.check = _check,                                           \
> +        .link.flags = _flags,                                           \
maybe we shouldn't have custom _check and _flags fields as majority of devices
use qdev_prop_allow_set_link_before_realize + OBJ_PROP_LINK_UNREF_ON_RELEASE
policies. That will save us ~2LOC per property of boiler plate code.

I've looked at current device link usage and there is only few that actually
use or need custom check/flags and several are misusing object_property_allow_set_link()
where they should use qdev_prop_allow_set_link_before_realize().

We could leave alone exceptions that require custom check/flags as is
or provide DEFINE_PROP_LINK_CUSTOM() for a few that actually need it and fix
ones that misuse it.

There is a bunch of board code that uses links but that's not for Device
so it's not related to this macro anyways.

> +        .link_type  = _type,                                            \
> +        }
> +
>  #define DEFINE_PROP_UINT8(_n, _s, _f, _d)                       \
>      DEFINE_PROP_UNSIGNED(_n, _s, _f, _d, qdev_prop_uint8, uint8_t)
>  #define DEFINE_PROP_UINT16(_n, _s, _f, _d)                      \