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@xxxxxxxxxxxxxxxxxx>
---
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
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