[libvirt] [PATCH] migrate VMs between different-endian hosts

[Stefan Berger]

On 04/12/2011 02:05 AM, Daniel Veillard wrote:
> On Mon, Apr 11, 2011 at 11:46:55AM -0600, Eric Blake wrote:
>> On 04/11/2011 07:36 AM, Daniel Veillard wrote:
>>>>>> @@ -3097,6 +3107,11 @@ qemuDomainSaveImageOpen(struct qemud_dri
>>>>>>       }
>>>>>>
>>>>>>       if (header.version>   QEMUD_SAVE_VERSION) {
>>>>>> +        /* convert endianess and try again */
>>>>>> +        bswap_header(&header);
>>>>>> +    }
>>>>>    Hum, isn't there a more reliable way to detect the change of
>>>>> endianness ? That's a bit fishy IMHO :-)
>>>> The problem is that the header should not have been written in a
>>>> hosts' native format. So what can go wrong? QEMUD_SAVE_VERSION is
>>>> '2'. Either we find 1 or 2 here and go ahead and accept it 'as-is'.
>>>> Otherwise anything bigger than 3 is not accepted and swapped. 3 then
>>>> becomes 0x03 00 00 00 and is discarded. 0x 02 00 00 00 would be
>>>> swapped to '2' and accepted.
>>>    yeah, I understand, okay,
>> Should we be writing the header in a particular byte order, regardless
>> of host endianness?  Or does that require bumping the header version to
>> 3 anyways?
>    The thing I'm worried about is that by bumping older versions won't
> be able to restore the new dumps, and that could be a serious issue on
> shared storage. We are not introducing a new feature, so I thin we need
> to preserve forward compatibility. The patch as is is minimal but
> achieves it.
>
Do you want to accept the patch ?

    Stefan