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

On 04/10/2011 11:09 PM, Daniel Veillard wrote: >On Sat, Apr 09, 2011 at 11:48:41AM -0400, Stefan Berger wrote: >>This patch enables the migration of Qemu VMs between hosts of >>different endianess. I tested this by migrating a i686 VM between a >>x86 and ppc64 host. > OMG, there is really a use case for this :-) ? :-) There may be other architectures that run more efficiently than an x86 one.

Btw, my use case is 'testing'.

>>@@ -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.