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.
Daniel
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Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/
daniel@xxxxxxxxxxxx | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library http://libvirt.org/
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