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

[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?

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).

> 
> >> +#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? 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);
#if defined(CPU_SAVE_VERSION)
    register_savevm(NULL, "cpu", cpu_index, CPU_SAVE_VERSION,
                     cpu_save, cpu_load, env);
#endif
    if (cc->vmsd) {
        vmstate_register(NULL, cpu_index, cc->vmsd, cpu);
    }
}

If we want to catch architectures that don't set CPU_SAVE_VERSION but
also don't register any vmsd (is this the bug you are trying to catch?),
we could do this:

#if defined(CPU_SAVE_VERSION)
    register_savevm(NULL, "cpu", cpu_index, CPU_SAVE_VERSION,
                     cpu_save, cpu_load, env);
#elif !defined(CONFIG_USER_ONLY)
    assert(cc->vmsd);
#endif
    if (cc->vmsd) {
        vmstate_register(NULL, cpu_index, cc->vmsd, cpu);
    }


> 
> Regards,
> Andreas
> 
> >> +    if (cc->vmsd != NULL) {
> >> +        vmstate_register(NULL, cpu_index, cc->vmsd, cpu);
> >> +    }
> >> +#endif
> >>  #endif
> >>  }
> >>  
> >> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> >> index 46f2247..b870752 100644
> >> --- a/include/qom/cpu.h
> >> +++ b/include/qom/cpu.h
> >> @@ -43,6 +43,7 @@ typedef struct CPUState CPUState;
> >>   * @class_by_name: Callback to map -cpu command line model name to an
> >>   * instantiatable CPU type.
> >>   * @reset: Callback to reset the #CPUState to its initial state.
> >> + * @vmsd: State description for migration.
> >>   *
> >>   * Represents a CPU family or model.
> >>   */
> >> @@ -54,6 +55,8 @@ typedef struct CPUClass {
> >>      ObjectClass *(*class_by_name)(const char *cpu_model);
> >>  
> >>      void (*reset)(CPUState *cpu);
> >> +
> >> +    const struct VMStateDescription *vmsd;
> >>  } CPUClass;
> >>  
> >>  struct KVMState;
> >> -- 
> >> 1.7.10.4
> 
> -- 
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
> GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg

-- 
Eduardo