Re: [Qemu-devel] [PATCH 1/2] migration: allow configuration section to be optional

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Mon, 15 Feb 2016 12:23:39 +0100
Laurent Vivier <lvivier@redhat.com> wrote:

> On 15/02/2016 11:15, Greg Kurz wrote:
> > Since QEMU 2.4, the migration stream begins with a configuration section.
> > It is known to break migration of pseries machine from older QEMU. It is
> > possible to fix this in the pseries compat code but it will then break
> > migration of old pseries from latest QEMU.
> > 
> > As an alternative, this patch introduces a new machine property which
> > allows to ignore the abscence of configuration section during incoming
> > migration. It boils to adding:
> > 
> > 	-machine config-section=off
> > 
> > Using this property only makes sense when migrating from an older
> > QEMU. It has no effect on outgoing migration.  
> 
> I think this is not true: migrating a pseries-2.3 machine from a
> qemu-2.4 to a qemu-2.3 must not send the configuration section because
> the qemu-2.3 will not be able to decode it.
> 

I did not mind to also fix backward compatibility... is it mandatory ?

> 2016-02-15T11:22:08.645978Z qemu-system-ppc64: Unknown savevm section type 7
> 2016-02-15T11:22:08.646041Z qemu-system-ppc64: load of migration failed:
> Invalid argument
> 
> [This is the result without your patch]
> 
> Laurent
> > 
> > Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > ---
> >  hw/core/machine.c   |   21 +++++++++++++++++++++
> >  include/hw/boards.h |    1 +
> >  migration/savevm.c  |   21 +++++++++++++++------
> >  qemu-options.hx     |    3 ++-
> >  4 files changed, 39 insertions(+), 7 deletions(-)
> > 
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index 6d1a0d8eebc4..4a7322988fb5 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -312,6 +312,20 @@ static bool machine_get_suppress_vmdesc(Object *obj, Error **errp)
> >      return ms->suppress_vmdesc;
> >  }
> >  
> > +static void machine_set_config_section(Object *obj, bool value, Error **errp)
> > +{
> > +    MachineState *ms = MACHINE(obj);
> > +
> > +    ms->config_section = value;
> > +}
> > +
> > +static bool machine_get_config_section(Object *obj, Error **errp)
> > +{
> > +    MachineState *ms = MACHINE(obj);
> > +
> > +    return ms->config_section;
> > +}
> > +
> >  static int error_on_sysbus_device(SysBusDevice *sbdev, void *opaque)
> >  {
> >      error_report("Option '-device %s' cannot be handled by this machine",
> > @@ -365,6 +379,7 @@ static void machine_initfn(Object *obj)
> >      ms->kvm_shadow_mem = -1;
> >      ms->dump_guest_core = true;
> >      ms->mem_merge = true;
> > +    ms->config_section = true;
> >  
> >      object_property_add_str(obj, "accel",
> >                              machine_get_accel, machine_set_accel, NULL);
> > @@ -467,6 +482,12 @@ static void machine_initfn(Object *obj)
> >      object_property_set_description(obj, "suppress-vmdesc",
> >                                      "Set on to disable self-describing migration",
> >                                      NULL);
> > +    object_property_add_bool(obj, "config-section",
> > +                             machine_get_config_section,
> > +                             machine_set_config_section, NULL);
> > +    object_property_set_description(obj, "config-section",
> > +                                    "Set on/off to accept migration with/without configuration section",
> > +                                    NULL);
> >  
> >      /* Register notifier when init is done for sysbus sanity checks */
> >      ms->sysbus_notifier.notify = machine_init_notify;
> > diff --git a/include/hw/boards.h b/include/hw/boards.h
> > index 0f30959e2e3b..853bb5905ec1 100644
> > --- a/include/hw/boards.h
> > +++ b/include/hw/boards.h
> > @@ -128,6 +128,7 @@ struct MachineState {
> >      char *firmware;
> >      bool iommu;
> >      bool suppress_vmdesc;
> > +    bool config_section;
> >  
> >      ram_addr_t ram_size;
> >      ram_addr_t maxram_size;
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index 94f2894243ce..3795489aeaec 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -1847,6 +1847,12 @@ static int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis)
> >      return 0;
> >  }
> >  
> > +static bool must_receive_configuration(void)
> > +{
> > +    MachineState *machine = MACHINE(qdev_get_machine());
> > +    return machine->config_section;
> > +}
> > +
> >  int qemu_loadvm_state(QEMUFile *f)
> >  {
> >      MigrationIncomingState *mis = migration_incoming_get_current();
> > @@ -1876,15 +1882,18 @@ int qemu_loadvm_state(QEMUFile *f)
> >      }
> >  
> >      if (!savevm_state.skip_configuration) {
> > -        if (qemu_get_byte(f) != QEMU_VM_CONFIGURATION) {
> > +        if (qemu_peek_byte(f, 0) == QEMU_VM_CONFIGURATION) {
> > +            qemu_file_skip(f, 1);
> > +            ret = vmstate_load_state(f, &vmstate_configuration, &savevm_state,
> > +                                     0);
> > +
> > +            if (ret) {
> > +                return ret;
> > +            }
> > +        } else if (must_receive_configuration()) {
> >              error_report("Configuration section missing");
> >              return -EINVAL;
> >          }
> > -        ret = vmstate_load_state(f, &vmstate_configuration, &savevm_state, 0);
> > -
> > -        if (ret) {
> > -            return ret;
> > -        }
> >      }
> >  
> >      ret = qemu_loadvm_state_main(f, mis);
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 2f0465eeb1d1..10cd64dc266b 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -43,7 +43,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
> >      "                aes-key-wrap=on|off controls support for AES key wrapping (default=on)\n"
> >      "                dea-key-wrap=on|off controls support for DEA key wrapping (default=on)\n"
> >      "                suppress-vmdesc=on|off disables self-describing migration (default=off)\n"
> > -    "                nvdimm=on|off controls NVDIMM support (default=off)\n",
> > +    "                nvdimm=on|off controls NVDIMM support (default=off)\n"
> > +    "                config-section=on|off migration requires configuration section (default=on)\n",
> >      QEMU_ARCH_ALL)
> >  STEXI
> >  @item -machine [type=]@var{name}[,prop=@var{value}[,...]]
> > 
> >   
>