Re: [Xen-devel] [PATCH 5/6] libxl: allow a generation ID to be specified at domain creation

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 11/06/14 12:01, Ian Campbell wrote:
> On Wed, 2014-06-11 at 11:53 +0100, David Vrabel wrote:
>> On 11/06/14 09:22, Ian Campbell wrote:
>>> On Tue, 2014-06-10 at 18:59 +0100, David Vrabel wrote:
>>>> On 10/06/14 12:01, Ian Campbell wrote:
>>>>> On Tue, 2014-06-03 at 14:15 +0100, David Vrabel wrote:
>>>>> Should we consider calling the API field name something more specific,
>>>>> like "ms_vgid"? I'm thinking of the case where some other OS vendor
>>>>> reinvents the wheel. (I don't care about the internals, just the API).
>>>>
>>>> generation_id matches the platform/generation-id xenstore key so I would
>>>> keep the libxl field name as-is.
>>>
>>> One is an internal implementation detail (we can update libx? and
>>> hvmloader in parallel if we have to) while the other is a stable API.
>>
>> The specification is for a generic, non-Microsoft specific ACPI device
>> so I don't see the need to include ms_ in the field name.
> 
> The name should reflect the spec then. acpi_vm_gen_counter perhaps
> (matching the ACPI _CID)

It does match the spec;  "Generation ID" is the name of the feature.
Using acpi_vm_gen_counter would just be confusing because the device
does not provide a counter.

>>>>> Do you not need to worry about endianess when memcpy'ing out of a uuid?
>>>>
>>>> No. The conversion of uuid to the two 64-bit integers is arbitrary, it
>>>> need only be consistent.  The integers in guest memory are in native
>>>> endianness.
>>>
>>> OK. I was wondering if we might want to preserve the byte order so as
>>> not to trample any UUID format which is used.
>>
>> The specification doesn't require that the ID is a UUID.
> 
> True. It does say "cryptographically random integer value". Are you sure
> that the result of libxl_uuid_generate meets that standard (rather than
> say one of the non-crypto schemes for generating uniqueness)?

Yes (although it does only provide 122 bits of randomness but I think
the trade-off of a convenient, UUID-base interface is worth it).

David

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