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

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.


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