Re: [Xen-devel] [PATCH v7 32/32] libxl: add support for migrating HVM guests without a device model

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 02/10/15 a les 20.56, Andrew Cooper ha escrit:
> On 02/10/15 16:49, Roger Pau Monne wrote:
>> Only some minor libxl changes are needed in order to be able to migrate HVM
>> guests without a device model, no hypervisor changes are needed.
>>
>> This change prevents sending the emulator context if the device model
>> version is set to none.
>>
>> Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
>> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
>> Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
>> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
>> ---
>>  tools/libxl/libxl_dom.c          | 3 +++
>>  tools/libxl/libxl_dom_suspend.c  | 2 ++
>>  tools/libxl/libxl_stream_write.c | 8 +++++++-
>>  3 files changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
>> index 7e8ae14..b40d744 100644
>> --- a/tools/libxl/libxl_dom.c
>> +++ b/tools/libxl/libxl_dom.c
>> @@ -1310,6 +1310,9 @@ void libxl__domain_suspend_common_switch_qemu_logdirty
>>      case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
>>          domain_suspend_switch_qemu_xen_logdirty(domid, enable, shs);
>>          break;
>> +    case LIBXL_DEVICE_MODEL_VERSION_NONE:
>> +        libxl__xc_domain_saverestore_async_callback_done(egc, shs, 0);
>> +        break;
>>      default:
>>          LOG(ERROR,"logdirty switch failed"
>>              ", no valid device model version found, abandoning suspend");
>> diff --git a/tools/libxl/libxl_dom_suspend.c 
>> b/tools/libxl/libxl_dom_suspend.c
>> index 4cc01ad..3313ad1 100644
>> --- a/tools/libxl/libxl_dom_suspend.c
>> +++ b/tools/libxl/libxl_dom_suspend.c
>> @@ -43,6 +43,8 @@ int libxl__domain_suspend_device_model(libxl__gc *gc,
>>          if (ret)
>>              unlink(filename);
>>          break;
>> +    case LIBXL_DEVICE_MODEL_VERSION_NONE:
>> +        break;
>>      default:
>>          return ERROR_INVAL;
>>      }
>> diff --git a/tools/libxl/libxl_stream_write.c 
>> b/tools/libxl/libxl_stream_write.c
>> index 52a60d7..5551560 100644
>> --- a/tools/libxl/libxl_stream_write.c
>> +++ b/tools/libxl/libxl_stream_write.c
>> @@ -232,6 +232,9 @@ void libxl__stream_write_start(libxl__egc *egc,
>>              stream->emu_sub_hdr.id = EMULATOR_QEMU_UPSTREAM;
>>              break;
>>  
>> +        case LIBXL_DEVICE_MODEL_VERSION_NONE:
>> +            break;
>> +
>>          default:
>>              rc = ERROR_FAIL;
>>              LOG(ERROR, "Unknown emulator for HVM domain");
>> @@ -387,8 +390,11 @@ static void emulator_xenstore_record_done(libxl__egc 
>> *egc,
>>                                            libxl__stream_write_state *stream)
>>  {
>>      libxl__domain_suspend_state *dss = stream->dss;
>> +    STATE_AO_GC(stream->ao);
>>  
>> -    if (dss->type == LIBXL_DOMAIN_TYPE_HVM)
>> +    if (dss->type == LIBXL_DOMAIN_TYPE_HVM &&
>> +        libxl__device_model_version_running(gc, dss->domid) !=
>> +        LIBXL_DEVICE_MODEL_VERSION_NONE)
>>          write_emulator_context_record(egc, stream);
>>      else {
>>          if (stream->in_checkpoint)
> 
> I think a few more changes are needed to make this robust.
> 
> write_emulator_xenstore_record() needs an early check for
> LIBXL_DEVICE_MODEL_VERSION_NONE and omit the call to
> libxl__save_emulator_xenstore_data() (which is only needed because
> qemu-upstream has a layering violation in its save format)
> 
> Instead of patching emulator_xenstore_record_done(), in the hunk above,
> I would suggest having another early check and continue in
> write_emulator_context_record()

I've done so and bailed early on both functions, without touching
emulator_xenstore_record_done.

> Also, you need to patch the EMULATOR_* cases in
> libxl_stream_read.c:process_record() to bail with a hard error if
> records received for a domain configured to have no emulators.

Ack, I've added checks in both REC_TYPE_EMULATOR_XENSTORE_DATA and
REC_TYPE_EMULATOR_CONTEXT. Will send a new version.

Thanks, Roger.


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