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

[Laurent Vivier <lvivier@redhat.com>]

On 15/02/2016 13:58, Greg Kurz wrote:
> 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 ?

I don't know, but as a user I would like to be able to do that (and it
is possible in the other cases).

And I think the fix could be smaller: something like just setting
"savevm_state.skip_configuration" to the value of "config-section".
[I don't know if it is as simple as it looks...]

Laurent
> 
>> 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}[,...]]
>>>
>>>   
>>
>