Re: [Qemu-devel] [PATCH v2 3/6] migration: move global_state.optional out

[Eduardo Habkost]

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 <address@hidden>
> ---
>  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