[libvirt] [PATCH] conf: Fix backwards migration of pSeries guests

[Andrea Bolognani]

Recent commits made it so that pci-root controllers for
pSeries guests are automatically assigned the
spapr-pci-host-bridge model name; however, that prevents
guests to migrate to older versions of libvirt which don't
know about that model name at all, which at the moment is
all of them :)

To avoid the issue, just strip the model name from PHBs
when formatting the migratable XML; guests that use more
than one PHB are not going to be migratable anyway.

Signed-off-by: Andrea Bolognani <abologna at redhat.com>
---
 src/conf/domain_conf.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 9320794..21bd7c7 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -21919,7 +21919,20 @@ virDomainControllerDefFormat(virBufferPtr buf,
     }
 
     if (def->type == VIR_DOMAIN_CONTROLLER_TYPE_PCI) {
-        if (def->opts.pciopts.modelName != VIR_DOMAIN_CONTROLLER_PCI_MODEL_NAME_NONE) {
+        bool formatModelName = true;
+
+        if (def->opts.pciopts.modelName == VIR_DOMAIN_CONTROLLER_PCI_MODEL_NAME_NONE)
+            formatModelName = false;
+
+        /* Don't format the model name for PHBs when migrating so that
+         * guests that only use the default one can be migrated to older
+         * libvirt version which don't know about PHBs at all */
+        if (virDomainControllerIsPCIHostBridge(def) &&
+            flags & VIR_DOMAIN_DEF_FORMAT_MIGRATABLE) {
+            formatModelName = false;
+        }
+
+        if (formatModelName) {
             modelName = virDomainControllerPCIModelNameTypeToString(def->opts.pciopts.modelName);
             if (!modelName) {
                 virReportError(VIR_ERR_INTERNAL_ERROR,
-- 
2.7.5