Put it into MigrationState then we can use the properties to specify
whether to enable storing global state.

Removing global_state_set_optional() since now we can use HW_COMPAT_2_3
for x86/power in general, and the register_compat_prop() for xen_init().

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/i386/pc_piix.c             |  1 -
 hw/ppc/spapr.c                |  1 -
 hw/xen/xen-common.c           |  8 +++++++-
 include/hw/compat.h           |  4 ++++
 include/migration/migration.h |  7 ++++++-
 migration/migration.c         | 24 ++++++++++++++++--------
 6 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 2234bd0..c83cec5 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -317,7 +317,6 @@ static void pc_compat_2_3(MachineState *machine)
     if (kvm_enabled()) {
         pcms->smm = ON_OFF_AUTO_OFF;
     }
-    global_state_set_optional();
     savevm_skip_configuration();
 }
 
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index ab3aab1..3e78bb9 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -3593,7 +3593,6 @@ static void spapr_machine_2_3_instance_options(MachineState *machine)
 {
     spapr_machine_2_4_instance_options(machine);
     savevm_skip_section_footers();
-    global_state_set_optional();
     savevm_skip_configuration();
 }
 
diff --git a/hw/xen/xen-common.c b/hw/xen/xen-common.c
index 0bed577..8240d50 100644
--- a/hw/xen/xen-common.c
+++ b/hw/xen/xen-common.c
@@ -138,7 +138,13 @@ static int xen_init(MachineState *ms)
     }
     qemu_add_vm_change_state_handler(xen_change_state_handler, NULL);
 
-    global_state_set_optional();
+    /*
+     * TODO: make sure global MigrationState has not yet been created
+     * (otherwise the compat trick won't work). For now we are in
+     * configure_accelerator() so we are mostly good. Better to
+     * confirm that in the future.
+     */
+    register_compat_prop("migration", "store-global-state", "off");
     savevm_skip_configuration();
     savevm_skip_section_footers();
 
diff --git a/include/hw/compat.h b/include/hw/compat.h
index 400c64b..5b5c8de 100644
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -177,6 +177,10 @@
         .driver   = TYPE_PCI_DEVICE,\
         .property = "x-pcie-lnksta-dllla",\
         .value    = "off",\
+    },{\
+        .driver   = "migration",\
+        .property = "store-global-state",\
+        .value    = "off",\
     },
 
 #define HW_COMPAT_2_2 \
diff --git a/include/migration/migration.h b/include/migration/migration.h
index bd0186c..d3ec719 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -162,6 +162,12 @@ struct MigrationState
     /* Do we have to clean up -b/-i from old migrate parameters */
     /* This feature is deprecated and will be removed */
     bool must_remove_block_options;
+
+    /*
+     * Global switch on whether we need to store the global state
+     * during migration.
+     */
+    bool store_global_state;
 };
 
 void migrate_set_state(int *state, int old_state, int new_state);
@@ -240,7 +246,6 @@ size_t ram_control_save_page(QEMUFile *f, ram_addr_t block_offset,
 
 void savevm_skip_section_footers(void);
 void register_global_state(void);
-void global_state_set_optional(void);
 void savevm_skip_configuration(void);
 int global_state_store(void);
 void global_state_store_running(void);
diff --git a/migration/migration.c b/migration/migration.c
index 98b77e2..79d886c 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -138,13 +138,13 @@ void migration_incoming_state_destroy(void)
 
 
 typedef struct {
-    bool optional;
     uint32_t size;
     uint8_t runstate[100];
     RunState state;
     bool received;
 } GlobalState;
 
+/* This is only used if MigrationState.store_global_state is set. */
 static GlobalState global_state;
 
 int global_state_store(void)
@@ -175,19 +175,13 @@ static RunState global_state_get_runstate(void)
     return global_state.state;
 }
 
-void global_state_set_optional(void)
-{
-    global_state.optional = true;
-}
-
 static bool global_state_needed(void *opaque)
 {
     GlobalState *s = opaque;
     char *runstate = (char *)s->runstate;
 
     /* If it is not optional, it is mandatory */
-
-    if (s->optional == false) {
+    if (migrate_get_current()->store_global_state) {
         return true;
     }
 
@@ -2107,6 +2101,19 @@ void migrate_fd_connect(MigrationState *s)
     s->migration_thread_running = true;
 }
 
+static Property migration_properties[] = {
+    DEFINE_PROP_BOOL("store-global-state", MigrationState,
+                     store_global_state, true),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void migration_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->props = migration_properties;
+}
+
 static void migration_instance_init(Object *obj)
 {
     MigrationState *ms = MIGRATION_OBJ(obj);
@@ -2131,6 +2138,7 @@ static void migration_instance_init(Object *obj)
 static const TypeInfo migration_type = {
     .name = TYPE_MIGRATION,
     .parent = TYPE_DEVICE,
+    .class_init = migration_class_init,
     .class_size = sizeof(MigrationClass),
     .instance_size = sizeof(MigrationState),
     .instance_init = migration_instance_init,
-- 
2.7.4

Peter Xu <peterx@redhat.com> wrote:
> Put it into MigrationState then we can use the properties to specify
> whether to enable storing global state.
>
> Removing global_state_set_optional() since now we can use HW_COMPAT_2_3
> for x86/power in general, and the register_compat_prop() for xen_init().
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Yeap, that is what I had in mind.

Reviewed-by: Juan Quintela <quintela@redhat.com>

On Fri, Jun 09, 2017 at 11:48:59AM +0800, Peter Xu wrote:
> Put it into MigrationState then we can use the properties to specify
> whether to enable storing global state.
> 
> Removing global_state_set_optional() since now we can use HW_COMPAT_2_3
> for x86/power in general, and the register_compat_prop() for xen_init().
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  hw/i386/pc_piix.c             |  1 -
>  hw/ppc/spapr.c                |  1 -
>  hw/xen/xen-common.c           |  8 +++++++-
>  include/hw/compat.h           |  4 ++++
>  include/migration/migration.h |  7 ++++++-
>  migration/migration.c         | 24 ++++++++++++++++--------
>  6 files changed, 33 insertions(+), 12 deletions(-)
> 
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index 2234bd0..c83cec5 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -317,7 +317,6 @@ static void pc_compat_2_3(MachineState *machine)
>      if (kvm_enabled()) {
>          pcms->smm = ON_OFF_AUTO_OFF;
>      }
> -    global_state_set_optional();
>      savevm_skip_configuration();
>  }
>  
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index ab3aab1..3e78bb9 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -3593,7 +3593,6 @@ static void spapr_machine_2_3_instance_options(MachineState *machine)
>  {
>      spapr_machine_2_4_instance_options(machine);
>      savevm_skip_section_footers();
> -    global_state_set_optional();
>      savevm_skip_configuration();
>  }

This is a good thing: makes the migration behavior of the
machine-types introspectable in compat_props.

I suggest moving this part (and all the rest except the new
register_compat_prop() call below) to a separate patch, because
it is an improvement on its own.

>  
> diff --git a/hw/xen/xen-common.c b/hw/xen/xen-common.c
> index 0bed577..8240d50 100644
> --- a/hw/xen/xen-common.c
> +++ b/hw/xen/xen-common.c
> @@ -138,7 +138,13 @@ static int xen_init(MachineState *ms)
>      }
>      qemu_add_vm_change_state_handler(xen_change_state_handler, NULL);
>  
> -    global_state_set_optional();
> +    /*
> +     * TODO: make sure global MigrationState has not yet been created
> +     * (otherwise the compat trick won't work). For now we are in
> +     * configure_accelerator() so we are mostly good. Better to
> +     * confirm that in the future.
> +     */

So, this makes accelerator initialization very sensitive to
ordering.

> +    register_compat_prop("migration", "store-global-state", "off");

It's already hard to track down machine-type stuff that is
initialized at machine->init() time but it's not introspectable,
let's not do the same mistake with accelerators.

Can't this be solved by a AcceleratorClass::global_props field,
so we are sure there's a single place in the code where globals
are registered?  (Currently, they are all registered by the few
lines around the machine_register_compat_props() call in main()).

I think I see other use cases for a new
AcceleratorClass::global_props field.  e.g.: replacing
kvm_default_props and tcg_default_props in target/i386/cpu.c.

>      savevm_skip_configuration();
>      savevm_skip_section_footers();
>  
> diff --git a/include/hw/compat.h b/include/hw/compat.h
> index 400c64b..5b5c8de 100644
> --- a/include/hw/compat.h
> +++ b/include/hw/compat.h
> @@ -177,6 +177,10 @@
>          .driver   = TYPE_PCI_DEVICE,\
>          .property = "x-pcie-lnksta-dllla",\
>          .value    = "off",\
> +    },{\
> +        .driver   = "migration",\
> +        .property = "store-global-state",\
> +        .value    = "off",\
>      },
>  
>  #define HW_COMPAT_2_2 \
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index bd0186c..d3ec719 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -162,6 +162,12 @@ struct MigrationState
>      /* Do we have to clean up -b/-i from old migrate parameters */
>      /* This feature is deprecated and will be removed */
>      bool must_remove_block_options;
> +
> +    /*
> +     * Global switch on whether we need to store the global state
> +     * during migration.
> +     */
> +    bool store_global_state;
>  };
>  
>  void migrate_set_state(int *state, int old_state, int new_state);
> @@ -240,7 +246,6 @@ size_t ram_control_save_page(QEMUFile *f, ram_addr_t block_offset,
>  
>  void savevm_skip_section_footers(void);
>  void register_global_state(void);
> -void global_state_set_optional(void);
>  void savevm_skip_configuration(void);
>  int global_state_store(void);
>  void global_state_store_running(void);
> diff --git a/migration/migration.c b/migration/migration.c
> index 98b77e2..79d886c 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -138,13 +138,13 @@ void migration_incoming_state_destroy(void)
>  
>  
>  typedef struct {
> -    bool optional;
>      uint32_t size;
>      uint8_t runstate[100];
>      RunState state;
>      bool received;
>  } GlobalState;
>  
> +/* This is only used if MigrationState.store_global_state is set. */
>  static GlobalState global_state;
>  
>  int global_state_store(void)
> @@ -175,19 +175,13 @@ static RunState global_state_get_runstate(void)
>      return global_state.state;
>  }
>  
> -void global_state_set_optional(void)
> -{
> -    global_state.optional = true;
> -}
> -
>  static bool global_state_needed(void *opaque)
>  {
>      GlobalState *s = opaque;
>      char *runstate = (char *)s->runstate;
>  
>      /* If it is not optional, it is mandatory */
> -
> -    if (s->optional == false) {
> +    if (migrate_get_current()->store_global_state) {
>          return true;
>      }
>  
> @@ -2107,6 +2101,19 @@ void migrate_fd_connect(MigrationState *s)
>      s->migration_thread_running = true;
>  }
>  
> +static Property migration_properties[] = {
> +    DEFINE_PROP_BOOL("store-global-state", MigrationState,
> +                     store_global_state, true),
> +    DEFINE_PROP_END_OF_LIST(),
> +};
> +
> +static void migration_class_init(ObjectClass *klass, void *data)
> +{
> +    DeviceClass *dc = DEVICE_CLASS(klass);
> +
> +    dc->props = migration_properties;
> +}
> +
>  static void migration_instance_init(Object *obj)
>  {
>      MigrationState *ms = MIGRATION_OBJ(obj);
> @@ -2131,6 +2138,7 @@ static void migration_instance_init(Object *obj)
>  static const TypeInfo migration_type = {
>      .name = TYPE_MIGRATION,
>      .parent = TYPE_DEVICE,
> +    .class_init = migration_class_init,
>      .class_size = sizeof(MigrationClass),
>      .instance_size = sizeof(MigrationState),
>      .instance_init = migration_instance_init,
> -- 
> 2.7.4
> 
> 

-- 
Eduardo

Eduardo Habkost <ehabkost@redhat.com> wrote:
D> On Fri, Jun 09, 2017 at 11:48:59AM +0800, Peter Xu wrote:
>> Put it into MigrationState then we can use the properties to specify
>> whether to enable storing global state.
>> 
>> Removing global_state_set_optional() since now we can use HW_COMPAT_2_3
>> for x86/power in general, and the register_compat_prop() for xen_init().
>> 
>> Signed-off-by: Peter Xu <peterx@redhat.com>
>> ---
>>  hw/i386/pc_piix.c             |  1 -
>>  hw/ppc/spapr.c                |  1 -
>>  hw/xen/xen-common.c           |  8 +++++++-
>>  include/hw/compat.h           |  4 ++++
>>  include/migration/migration.h |  7 ++++++-
>>  migration/migration.c         | 24 ++++++++++++++++--------
>>  6 files changed, 33 insertions(+), 12 deletions(-)
>> 
>> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
>> index 2234bd0..c83cec5 100644
>> --- a/hw/i386/pc_piix.c
>> +++ b/hw/i386/pc_piix.c
>> @@ -317,7 +317,6 @@ static void pc_compat_2_3(MachineState *machine)
>>      if (kvm_enabled()) {
>>          pcms->smm = ON_OFF_AUTO_OFF;
>>      }
>> -    global_state_set_optional();
>>      savevm_skip_configuration();
>>  }
>>  
>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>> index ab3aab1..3e78bb9 100644
>> --- a/hw/ppc/spapr.c
>> +++ b/hw/ppc/spapr.c
>> @@ -3593,7 +3593,6 @@ static void spapr_machine_2_3_instance_options(MachineState *machine)
>>  {
>>      spapr_machine_2_4_instance_options(machine);
>>      savevm_skip_section_footers();
>> -    global_state_set_optional();
>>      savevm_skip_configuration();
>>  }
>
> This is a good thing: makes the migration behavior of the
> machine-types introspectable in compat_props.
>
> I suggest moving this part (and all the rest except the new
> register_compat_prop() call below) to a separate patch, because
> it is an improvement on its own.
>
>>  
>> diff --git a/hw/xen/xen-common.c b/hw/xen/xen-common.c
>> index 0bed577..8240d50 100644
>> --- a/hw/xen/xen-common.c
>> +++ b/hw/xen/xen-common.c
>> @@ -138,7 +138,13 @@ static int xen_init(MachineState *ms)
>>      }
>>      qemu_add_vm_change_state_handler(xen_change_state_handler, NULL);
>>  
>> -    global_state_set_optional();
>> +    /*
>> +     * TODO: make sure global MigrationState has not yet been created
>> +     * (otherwise the compat trick won't work). For now we are in
>> +     * configure_accelerator() so we are mostly good. Better to
>> +     * confirm that in the future.
>> +     */
>
> So, this makes accelerator initialization very sensitive to
> ordering.
>
>> +    register_compat_prop("migration", "store-global-state", "off");
>
> It's already hard to track down machine-type stuff that is
> initialized at machine->init() time but it's not introspectable,
> let's not do the same mistake with accelerators.
>
> Can't this be solved by a AcceleratorClass::global_props field,
> so we are sure there's a single place in the code where globals
> are registered?  (Currently, they are all registered by the few
> lines around the machine_register_compat_props() call in main()).
>
> I think I see other use cases for a new
> AcceleratorClass::global_props field.  e.g.: replacing
> kvm_default_props and tcg_default_props in target/i386/cpu.c.

That is the kind of discussion that I wanted to start.  Thanks.
For the migration point of view, we don't care *how* or *where* it is
implemented, just that it is easy to add new properties (call it
whatever name that you want).

And yes, making xen/kvm/tcg use QOM like everything else looks like a
good idea to me.

Later, Juan.

On Fri, Jun 09, 2017 at 10:40:10AM -0300, Eduardo Habkost wrote:
> On Fri, Jun 09, 2017 at 11:48:59AM +0800, Peter Xu wrote:
> > Put it into MigrationState then we can use the properties to specify
> > whether to enable storing global state.
> > 
> > Removing global_state_set_optional() since now we can use HW_COMPAT_2_3
> > for x86/power in general, and the register_compat_prop() for xen_init().
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  hw/i386/pc_piix.c             |  1 -
> >  hw/ppc/spapr.c                |  1 -
> >  hw/xen/xen-common.c           |  8 +++++++-
> >  include/hw/compat.h           |  4 ++++
> >  include/migration/migration.h |  7 ++++++-
> >  migration/migration.c         | 24 ++++++++++++++++--------
> >  6 files changed, 33 insertions(+), 12 deletions(-)
> > 
> > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > index 2234bd0..c83cec5 100644
> > --- a/hw/i386/pc_piix.c
> > +++ b/hw/i386/pc_piix.c
> > @@ -317,7 +317,6 @@ static void pc_compat_2_3(MachineState *machine)
> >      if (kvm_enabled()) {
> >          pcms->smm = ON_OFF_AUTO_OFF;
> >      }
> > -    global_state_set_optional();
> >      savevm_skip_configuration();
> >  }
> >  
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index ab3aab1..3e78bb9 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -3593,7 +3593,6 @@ static void spapr_machine_2_3_instance_options(MachineState *machine)
> >  {
> >      spapr_machine_2_4_instance_options(machine);
> >      savevm_skip_section_footers();
> > -    global_state_set_optional();
> >      savevm_skip_configuration();
> >  }
> 
> This is a good thing: makes the migration behavior of the
> machine-types introspectable in compat_props.
> 
> I suggest moving this part (and all the rest except the new
> register_compat_prop() call below) to a separate patch, because
> it is an improvement on its own.

Sure.

> 
> >  
> > diff --git a/hw/xen/xen-common.c b/hw/xen/xen-common.c
> > index 0bed577..8240d50 100644
> > --- a/hw/xen/xen-common.c
> > +++ b/hw/xen/xen-common.c
> > @@ -138,7 +138,13 @@ static int xen_init(MachineState *ms)
> >      }
> >      qemu_add_vm_change_state_handler(xen_change_state_handler, NULL);
> >  
> > -    global_state_set_optional();
> > +    /*
> > +     * TODO: make sure global MigrationState has not yet been created
> > +     * (otherwise the compat trick won't work). For now we are in
> > +     * configure_accelerator() so we are mostly good. Better to
> > +     * confirm that in the future.
> > +     */
> 
> So, this makes accelerator initialization very sensitive to
> ordering.
> 
> > +    register_compat_prop("migration", "store-global-state", "off");
> 
> It's already hard to track down machine-type stuff that is
> initialized at machine->init() time but it's not introspectable,
> let's not do the same mistake with accelerators.
> 
> Can't this be solved by a AcceleratorClass::global_props field,
> so we are sure there's a single place in the code where globals
> are registered?  (Currently, they are all registered by the few
> lines around the machine_register_compat_props() call in main()).
> 
> I think I see other use cases for a new
> AcceleratorClass::global_props field.  e.g.: replacing
> kvm_default_props and tcg_default_props in target/i386/cpu.c.

Hmm, this sounds nice.  Then we can also get rid of the TODO above.

Thanks for your suggestion and review! I'll see whether I can writeup
something as RFC for this.

-- 
Peter Xu

On Mon, Jun 12, 2017 at 04:18:06PM +0800, Peter Xu wrote:
> On Fri, Jun 09, 2017 at 10:40:10AM -0300, Eduardo Habkost wrote:
> > On Fri, Jun 09, 2017 at 11:48:59AM +0800, Peter Xu wrote:
> > > Put it into MigrationState then we can use the properties to specify
> > > whether to enable storing global state.
> > > 
> > > Removing global_state_set_optional() since now we can use HW_COMPAT_2_3
> > > for x86/power in general, and the register_compat_prop() for xen_init().
> > > 
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > > ---
> > >  hw/i386/pc_piix.c             |  1 -
> > >  hw/ppc/spapr.c                |  1 -
> > >  hw/xen/xen-common.c           |  8 +++++++-
> > >  include/hw/compat.h           |  4 ++++
> > >  include/migration/migration.h |  7 ++++++-
> > >  migration/migration.c         | 24 ++++++++++++++++--------
> > >  6 files changed, 33 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > > index 2234bd0..c83cec5 100644
> > > --- a/hw/i386/pc_piix.c
> > > +++ b/hw/i386/pc_piix.c
> > > @@ -317,7 +317,6 @@ static void pc_compat_2_3(MachineState *machine)
> > >      if (kvm_enabled()) {
> > >          pcms->smm = ON_OFF_AUTO_OFF;
> > >      }
> > > -    global_state_set_optional();
> > >      savevm_skip_configuration();
> > >  }
> > >  
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index ab3aab1..3e78bb9 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -3593,7 +3593,6 @@ static void spapr_machine_2_3_instance_options(MachineState *machine)
> > >  {
> > >      spapr_machine_2_4_instance_options(machine);
> > >      savevm_skip_section_footers();
> > > -    global_state_set_optional();
> > >      savevm_skip_configuration();
> > >  }
> > 
> > This is a good thing: makes the migration behavior of the
> > machine-types introspectable in compat_props.
> > 
> > I suggest moving this part (and all the rest except the new
> > register_compat_prop() call below) to a separate patch, because
> > it is an improvement on its own.
> 
> Sure.
> 
> > 
> > >  
> > > diff --git a/hw/xen/xen-common.c b/hw/xen/xen-common.c
> > > index 0bed577..8240d50 100644
> > > --- a/hw/xen/xen-common.c
> > > +++ b/hw/xen/xen-common.c
> > > @@ -138,7 +138,13 @@ static int xen_init(MachineState *ms)
> > >      }
> > >      qemu_add_vm_change_state_handler(xen_change_state_handler, NULL);
> > >  
> > > -    global_state_set_optional();
> > > +    /*
> > > +     * TODO: make sure global MigrationState has not yet been created
> > > +     * (otherwise the compat trick won't work). For now we are in
> > > +     * configure_accelerator() so we are mostly good. Better to
> > > +     * confirm that in the future.
> > > +     */
> > 
> > So, this makes accelerator initialization very sensitive to
> > ordering.
> > 
> > > +    register_compat_prop("migration", "store-global-state", "off");
> > 
> > It's already hard to track down machine-type stuff that is
> > initialized at machine->init() time but it's not introspectable,
> > let's not do the same mistake with accelerators.
> > 
> > Can't this be solved by a AcceleratorClass::global_props field,
> > so we are sure there's a single place in the code where globals
> > are registered?  (Currently, they are all registered by the few
> > lines around the machine_register_compat_props() call in main()).
> > 
> > I think I see other use cases for a new
> > AcceleratorClass::global_props field.  e.g.: replacing
> > kvm_default_props and tcg_default_props in target/i386/cpu.c.
> 
> Hmm, this sounds nice.  Then we can also get rid of the TODO above.
> 
> Thanks for your suggestion and review! I'll see whether I can writeup
> something as RFC for this.

After a second thought, I see these requirements are slightly
different.

For xen_init(), AccelClass::global_props may help since that's mainly
properties to be setup for TYPE_MIGRATION (let's assume it's okay that
MigrationState can be a QDev).

For kvm_default_props and tcg_default_props, AccelClass::global_props
may not help since they are setting up properties for TYPE_CPU, and
TYPE_CPU cannot really use global property features yet. :(

If finally we can have a new way (e.g., as you suggested in the other
thread, using a new INTERFACE to show that one QObject supports global
qdev properties) to allow TYPE_CPU to use global properties, then
these two requirements can merge. Otherwise IMHO we may still need to
keep the *_default_props in CPU codes.

Thanks,

-- 
Peter Xu