Re: [Qemu-devel] [PATCH qom-next v2 3/5] target-arm: Use parent classes for reset + realize

[Peter Crosthwaite]

Hi Igor,

On Thu, Jul 11, 2013 at 7:47 PM, Igor Mammedov <address@hidden> wrote:
> On Thu, 11 Jul 2013 11:47:16 +1000
> address@hidden wrote:
>
>> From: Peter Crosthwaite <address@hidden>
>>
>> ARMCPUClass is only needed for parent-class abstract function access.
>> Just use parent classes for reset and realize access and remove
>> ARMCPUClass completely.
>>
>> Signed-off-by: Peter Crosthwaite <address@hidden>
>> ---
>>
>>  target-arm/cpu-qom.h | 20 --------------------
>>  target-arm/cpu.c     | 16 +++++++---------
>>  2 files changed, 7 insertions(+), 29 deletions(-)
>>
>> diff --git a/target-arm/cpu-qom.h b/target-arm/cpu-qom.h
>> index ef6261f..bdad93a 100644
>> --- a/target-arm/cpu-qom.h
>> +++ b/target-arm/cpu-qom.h
>> @@ -24,28 +24,8 @@
>>
>>  #define TYPE_ARM_CPU "arm-cpu"
>>
>> -#define ARM_CPU_CLASS(klass) \
>> -    OBJECT_CLASS_CHECK(ARMCPUClass, (klass), TYPE_ARM_CPU)
>>  #define ARM_CPU(obj) \
>>      OBJECT_CHECK(ARMCPU, (obj), TYPE_ARM_CPU)
>> -#define ARM_CPU_GET_CLASS(obj) \
>> -    OBJECT_GET_CLASS(ARMCPUClass, (obj), TYPE_ARM_CPU)
>> -
>> -/**
>> - * ARMCPUClass:
>> - * @parent_realize: The parent class' realize handler.
>> - * @parent_reset: The parent class' reset handler.
>> - *
>> - * An ARM CPU model.
>> - */
>> -typedef struct ARMCPUClass {
>> -    /*< private >*/
>> -    CPUClass parent_class;
>> -    /*< public >*/
>> -
>> -    DeviceRealize parent_realize;
>> -    void (*parent_reset)(CPUState *cpu);
>> -} ARMCPUClass;
>>
>>  /**
>>   * ARMCPU:
>> diff --git a/target-arm/cpu.c b/target-arm/cpu.c
>> index ed53df8..ad5ec7b 100644
>> --- a/target-arm/cpu.c
>> +++ b/target-arm/cpu.c
>> @@ -60,7 +60,8 @@ static void cp_reg_reset(gpointer key, gpointer value, 
>> gpointer opaque)
>>  static void arm_cpu_reset(CPUState *s)
>>  {
>>      ARMCPU *cpu = ARM_CPU(s);
>> -    ARMCPUClass *acc = ARM_CPU_GET_CLASS(cpu);
>> +    CPUClass *cc_parent =
>> +            CPU_CLASS(object_class_get_parent_by_name(TYPE_ARM_CPU));
> Maybe object_class_get_parent_of_type() would be less confusing?
>
> This usage assumes that parent of TYPE_ARM_CPU is TYPE_CPU

It assumes that a parent (could be a grandparent on any level) is
TYPE_CPU not necessarily the direct parent.

> and if
> another TYPE_X added between them, it might break if TYPE_X doesn't
> re-implement this logic in its reset.

That's not really an issue. Assuming your example inheritance heirachy:

TYPE_ARM_CPU -> TYPE_X -> TYPE_CPU

If TYPE_X does not override reset, then TYPE_X inherits
TYPE_CPU::reset as its reset. When TYPE_ARM_CPU does
object_class_get_parent_by_name(TYPE_ARM_CPU), TYPE_X will be
returned, but it will call TYPE_CPU::reset through inheritance anyway.
If TYPE_X does implement a reset, then its TYPE_X's job to call parent
reset as well but that is no different to the status quo anyway.

>
> Could reset be modeled like DEVICE.instance_init() instead? Then
> no explicit access to parent from child would be needed and it
> still leaves possibility to override resets if parent->child
> propagation order is not desirable for a particular device.
>

I don't think thats a good idea. Then reset is inconsistent with other
deviceClass::foo APIs. Leave calling of the parent open coded for the
child to determine. Also the parent should not be allowed to force the
child to call its reset. The child should be able override an API
throwing the original away entirely. The child should also be able to
call the parent version when it wants, rather than us having to worry
about the need for multiple "post or pre" versions.

Regards,
Peter

>>      CPUARMState *env = &cpu->env;
>>
>>      if (qemu_loglevel_mask(CPU_LOG_RESET)) {
>> @@ -68,7 +69,7 @@ static void arm_cpu_reset(CPUState *s)
>>          log_cpu_state(env, 0);
>>      }
>>
>> -    acc->parent_reset(s);
>> +    cc_parent->reset(s);
>>
>>      memset(env, 0, offsetof(CPUARMState, breakpoints));
>>      g_hash_table_foreach(cpu->cp_regs, cp_reg_reset, cpu);
>> @@ -158,7 +159,8 @@ static void arm_cpu_finalizefn(Object *obj)
>>  static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
>>  {
>>      ARMCPU *cpu = ARM_CPU(dev);
>> -    ARMCPUClass *acc = ARM_CPU_GET_CLASS(dev);
>> +    DeviceClass *dc_parent =
>> +            DEVICE_CLASS(object_class_get_parent_by_name(TYPE_ARM_CPU));
>>      CPUARMState *env = &cpu->env;
>>
>>      /* Some features automatically imply others: */
>> @@ -209,7 +211,7 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
>> **errp)
>>
>>      cpu_reset(CPU(cpu));
>>
>> -    acc->parent_realize(dev, errp);
>> +    dc_parent->realize(dev, errp);
>>  }
>>
>>  /* CPU models */
>> @@ -803,14 +805,11 @@ static const ARMCPUInfo arm_cpus[] = {
>>
>>  static void arm_cpu_class_init(ObjectClass *oc, void *data)
>>  {
>> -    ARMCPUClass *acc = ARM_CPU_CLASS(oc);
>> -    CPUClass *cc = CPU_CLASS(acc);
>> +    CPUClass *cc = CPU_CLASS(oc);
>>      DeviceClass *dc = DEVICE_CLASS(oc);
>>
>> -    acc->parent_realize = dc->realize;
>>      dc->realize = arm_cpu_realizefn;
>>
>> -    acc->parent_reset = cc->reset;
>>      cc->reset = arm_cpu_reset;
>>
>>      cc->class_by_name = arm_cpu_class_by_name;
>> @@ -839,7 +838,6 @@ static const TypeInfo arm_cpu_type_info = {
>>      .instance_init = arm_cpu_initfn,
>>      .instance_finalize = arm_cpu_finalizefn,
>>      .abstract = true,
>> -    .class_size = sizeof(ARMCPUClass),
>>      .class_init = arm_cpu_class_init,
>>  };
>>
>
>