Re: [Qemu-devel] [PATCH for-3.2 v3 02/14] qom: make interface types abstract

[Igor Mammedov <imammedo@redhat.com>]

On Wed,  7 Nov 2018 16:36:40 +0400
Marc-André Lureau <marcandre.lureau@redhat.com> wrote:

> Interfaces don't have instance, let's make the interface type really
> abstract to avoid confusion.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  include/hw/acpi/acpi_dev_interface.h | 6 +-----
>  include/hw/arm/linux-boot-if.h       | 5 +----
>  include/hw/fw-path-provider.h        | 4 +---
>  include/hw/hotplug.h                 | 6 +-----
>  include/hw/intc/intc.h               | 4 +---
>  include/hw/ipmi/ipmi.h               | 4 +---
>  include/hw/isa/isa.h                 | 4 ----
>  include/hw/mem/memory-device.h       | 4 +---
>  include/hw/nmi.h                     | 4 +---
>  include/hw/stream.h                  | 4 +---
>  include/hw/timer/m48t59.h            | 4 +---
>  include/qom/object_interfaces.h      | 6 +-----
>  include/sysemu/tpm.h                 | 4 +---
>  target/arm/idau.h                    | 4 +---
>  tests/check-qom-interface.c          | 4 +---
>  15 files changed, 14 insertions(+), 53 deletions(-)
> 
> diff --git a/include/hw/acpi/acpi_dev_interface.h b/include/hw/acpi/acpi_dev_interface.h
> index dabf4c4fc9..43ff119179 100644
> --- a/include/hw/acpi/acpi_dev_interface.h
> +++ b/include/hw/acpi/acpi_dev_interface.h
> @@ -25,11 +25,7 @@ typedef enum {
>       INTERFACE_CHECK(AcpiDeviceIf, (obj), \
>                       TYPE_ACPI_DEVICE_IF)
>  
> -
> -typedef struct AcpiDeviceIf {
> -    /* <private> */
> -    Object Parent;
> -} AcpiDeviceIf;
> +typedef struct AcpiDeviceIf AcpiDeviceIf;
>  
>  void acpi_send_event(DeviceState *dev, AcpiEventStatusBits event);
>  
> diff --git a/include/hw/arm/linux-boot-if.h b/include/hw/arm/linux-boot-if.h
> index aba4479a14..7bbdfd1cc6 100644
> --- a/include/hw/arm/linux-boot-if.h
> +++ b/include/hw/arm/linux-boot-if.h
> @@ -16,10 +16,7 @@
>  #define ARM_LINUX_BOOT_IF(obj) \
>      INTERFACE_CHECK(ARMLinuxBootIf, (obj), TYPE_ARM_LINUX_BOOT_IF)
>  
> -typedef struct ARMLinuxBootIf {
> -    /*< private >*/
> -    Object parent_obj;
> -} ARMLinuxBootIf;
> +typedef struct ARMLinuxBootIf ARMLinuxBootIf;
I like how it makes interface truly opaque and removes the need for
structure declaration but:

 1: I'm not sure if it's acceptable thing to do from language point of view

 2: For a reader not aware of a trick, it's sort of confusing to have forward declaration but without structure itself. So if #1 is acceptable we probably should document interface trick in object.h

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