[libvirt] [PATCH] migrate VMs between different-endian hosts
Stefan Berger
stefanb at linux.vnet.ibm.com
Mon Apr 11 17:56:14 UTC 2011
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
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