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

[Stefan Berger]

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.

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);
+    }
+
+    if (header.version > QEMUD_SAVE_VERSION) {
          qemuReportError(VIR_ERR_OPERATION_FAILED,
                          _("image version is not supported (%d > %d)"),
                          header.version, QEMUD_SAVE_VERSION);