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'.
>> I am converting the 'int's in the VM's state header to uint32_t
>> assuming this doesn't break compatibility with existing deployments
>> other than Linux.
>>
>> Signed-off-by: Stefan Berger<stefanb at linux.vnet.ibm.com>
>>
>> ---
>> src/qemu/qemu_driver.c | 25 ++++++++++++++++++++-----
>> 1 file changed, 20 insertions(+), 5 deletions(-)
>>
>> Index: libvirt-acl/src/qemu/qemu_driver.c
>> ===================================================================
>> --- libvirt-acl.orig/src/qemu/qemu_driver.c
>> +++ libvirt-acl/src/qemu/qemu_driver.c
>> @@ -43,6 +43,7 @@
>> #include<sys/wait.h>
>> #include<sys/ioctl.h>
>> #include<sys/un.h>
>> +#include<byteswap.h>
>>
>>
>> #include "qemu_driver.h"
>> @@ -1881,13 +1882,22 @@ VIR_ENUM_IMPL(qemudSaveCompression, QEMU
>>
>> struct qemud_save_header {
>> char magic[sizeof(QEMUD_SAVE_MAGIC)-1];
>> - int version;
>> - int xml_len;
>> - int was_running;
>> - int compressed;
>> - int unused[15];
>> + uint32_t version;
>> + uint32_t xml_len;
>> + uint32_t was_running;
>> + uint32_t compressed;
>> + uint32_t unused[15];
>> };
>>
>> +static inline void
>> +bswap_header(struct qemud_save_header *hdr) {
>> + hdr->version = bswap_32(hdr->version);
>> + hdr->xml_len = bswap_32(hdr->xml_len);
>> + hdr->was_running = bswap_32(hdr->was_running);
>> + hdr->compressed = bswap_32(hdr->compressed);
>> +}
>> +
>> +
>> /* return -errno on failure, or 0 on success */
>> static int
>> qemuDomainSaveHeader(int fd, const char *path, char *xml,
>> @@ -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.
Stefan
>> + if (header.version> QEMUD_SAVE_VERSION) {
>> qemuReportError(VIR_ERR_OPERATION_FAILED,
>> _("image version is not supported (%d> %d)"),
>> header.version, QEMUD_SAVE_VERSION);
> Daniel
>