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

[Stefan Berger]

On 04/11/2011 01:46 PM, 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?
>
Would version 3 then simply mean to convert to 
version-3-standard-header-endianess and anything below just would fail 
if the hosts had different endianess ? No matter what, we'll have to 
have code to convert the version indicator alone.

    Stefan