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@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