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

[Andreas Färber]

Am 07.02.2013 19:27, schrieb 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.

Found a solution to both your suggestions, v2 coming up.

Andreas

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