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



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


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