Re: [Qemu-devel] [PATCH RFC qom-cpu-next 1/6] cpu: Register VMStateDescription through CPUState

[Andreas Färber]

Am 07.02.2013 19:22, schrieb Eduardo Habkost:
> On Thu, Feb 07, 2013 at 07:02:32PM +0100, Andreas Färber wrote:
>> Am 07.02.2013 18:46, schrieb Eduardo Habkost:
>>> On Thu, Feb 07, 2013 at 06:20:52PM +0100, Andreas Färber wrote:
>>>> Am 07.02.2013 17:40, schrieb Eduardo Habkost:
>>>>> On Sat, Feb 02, 2013 at 04:04:11PM +0100, Andreas Färber wrote:
>>>>>> In comparison to DeviceClass::vmsd, CPU VMState is split in two,
>>>>>> "cpu_common" and "cpu", and uses cpu_index as instance_id instead of -1.
>>>>>> Therefore add a CPU-specific CPUClass::vmsd field.
>>>>>>
>>>>>> Unlike the legacy CPUArchState registration, rather register CPUState.
>>>>>>
>>>>>> Signed-off-by: Juan Quintela <address@hidden>
>>>>>> Signed-off-by: Andreas Färber <address@hidden>
>>>>>> ---
>>>>>>  exec.c            |   13 +++++++++++--
>>>>>>  include/qom/cpu.h |    3 +++
>>>>>>  2 Dateien geändert, 14 Zeilen hinzugefügt(+), 2 Zeilen entfernt(-)
>>>>>>
>>>>>> diff --git a/exec.c b/exec.c
>>>>>> index b85508b..5eee174 100644
>>>>>> --- a/exec.c
>>>>>> +++ b/exec.c
>>>>>> @@ -219,7 +219,7 @@ void cpu_exec_init_all(void)
>>>>>>  #endif
>>>>>>  }
>>>>>>  
>>>>>> -#if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
>>>>>> +#if !defined(CONFIG_USER_ONLY)
>>>>>>  
>>>>>>  static int cpu_common_post_load(void *opaque, int version_id)
>>>>>>  {
>>>>>> @@ -266,6 +266,9 @@ CPUState *qemu_get_cpu(int index)
>>>>>>  void cpu_exec_init(CPUArchState *env)
>>>>>>  {
>>>>>>      CPUState *cpu = ENV_GET_CPU(env);
>>>>>> +#if !defined(CONFIG_USER_ONLY) && !defined(CPU_SAVE_VERSION)
>>>>>> +    CPUClass *cc = CPU_GET_CLASS(cpu);
>>>>>> +#endif
>>>>>>      CPUArchState **penv;
>>>>>>      int cpu_index;
>>>>>>  
>>>>>> @@ -290,10 +293,16 @@ void cpu_exec_init(CPUArchState *env)
>>>>>>  #if defined(CONFIG_USER_ONLY)
>>>>>>      cpu_list_unlock();
>>>>>>  #endif
>>>>>> -#if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
>>>>>> +#if !defined(CONFIG_USER_ONLY)
>>>>>>      vmstate_register(NULL, cpu_index, &vmstate_cpu_common, env);
>>>>>> +#if defined(CPU_SAVE_VERSION)
>>>>>>      register_savevm(NULL, "cpu", cpu_index, CPU_SAVE_VERSION,
>>>>>>                      cpu_save, cpu_load, env);
>>>>>
>>>>> What about introducing stub register_savevm() function in libqemustub.a,
>>>>> so we can eliminate the CONFIG_USER_ONLY ifdefs?
>>>>>
>>>>> (we already have vmstate_register()/vmstate_unregister() stubs).
>>>>
>>>> register_savevm() itself is not the issue, it's the VMStateDescription
>>>> itself with all its external references that would be quite some (IMO
>>>> useless) work to make available to *-user...
>>>
>>> Are you talking about the VMStateDescription struct declaration, or
>>> about actually setting the vmsd field?
>>
>> I'm talking about, e.g., #include "machine.c", i.e. VMStateDescription
>> vmstate_something = { ... }; something_else = &vmstate_something;.
>>
>> This broke horribly.
>>
>>> The struct declaration is available even if CONFIG_USER_ONLY is set. See
>>> qdev.c. It doesn't have any #ifdefs around
>>> vmstate_register()/vmstate_unregister() calls.
>>>
>>> I don't suggest we set the field to non-NULL if CONFIG_USER_ONLY is set
>>> (that would be difficult and unnecessary).
>>
>> That's what I was saying, yes.
>>
>>>>>> +#else
>>>>>
>>>>> Do we have any architecture that sets CPU_SAVE_VERSION _and_ sets
>>>>> cc->vmsd at the same time? If not, we could put the "if (cc->vmsd)
>>>>> vmstate_register()" part outside any #ifdef/#else block.
>>>>
>>>> They shouldn't. When this series and any follow-up by Juan himself were
>>>> applied, there would be no more CPU_SAVE_VERSION and all CPUs would
>>>> register a vmsd one way or another. Targets to be converted include ppc,
>>>> arm and sparc.
>>>>
>>>> Together with the final RFC patch in this series, doing it inside an
>>>> #else block avoids repeating the lax checks that have led alpha,
>>>> openrisc and a few others to not register things correctly.
>>>
>>> What exactly were the lax checks that have led them to not register
>>> things correctly?
>>
>> In short: Lack of patch 6.
>>
>> !defined(CPU_SAVE_VERSION) but implementing cpu_save/load when they
>> should've #define'd CPU_SAVE_VERSION.
>>
>> In turn I want to assure that when !defined(CPU_SAVE_VERSION)
>> implementing cpu_save/load leads to build error.
>>
>>> Would my suggestion below cause the same problems?
>>>
>>>> This is the
>>>> part of the patch that I adopted from Juan. I don't insist though.
>>>
>>> I am OK with "#ifdef CPU_SAVE_VERSION" #ifdef because it is for legacy
>>> code (and should be temporary, right?), but I think we can easily drop
>>> the #ifdefs around all the other lines. I mean, we can easily make the
>>> code look like this:
>>>
>>> void cpu_exec_init(CPUArchState *env)
>>> {
>>>     CPUState *cpu = ENV_GET_CPU(env);
>>>     CPUClass *cc = CPU_GET_CLASS(cpu);
>>>     [...]
>>>
>>>     vmstate_register(NULL, cpu_index, &vmstate_cpu_common, env);
>>
>> &vmstate_cpu_common will break for linux-user.
> 
> Oops. Then what about:
> 
> #if !defined(CONFIG_USER_ONLY)
> static const VMStateDescription vmstate_cpu_common { ... };
> #define cpu_common_vmsd (&vmstate_cpu_common)
> #else
> #define cpu_common_vmsd NULL
> #endif
> [...]
>      vmstate_register(NULL, cpu_index, cpu_common_vmsd, env);
> [...]
> 
> This pattern is similar to what I suggested for the code that
> initializes cc->vmsd on the target-specific class_init functions. I
> don't really love the way it looks, but I prefer #ifdefs on declarative
> parts of the code than inside functions. I wonder if we could simplify
> it further.

As commented on the x86 part I'm not quite happy with that pattern...

Is there a way we could keep the referencing local to the code using it,
i.e. have a single vmstate_dummy in *-user code that we can #define
vmstate_x86_cpu etc. to for CONFIG_USER_ONLY? I don't quite see where
and how, might require to define a file-local struct VMStateDescription
without fields or so.

Andreas

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