From 7e3b03cbdee6a9fc694046ea3c98c5cdef941c92 Mon Sep 17 00:00:00 2001
Message-Id: <7e3b03cbdee6a9fc694046ea3c98c5cdef941c92@dist-git>
From: Andrea Bolognani <abologna@redhat.com>
Date: Tue, 25 Jul 2017 10:29:27 +0200
Subject: [PATCH] conf: Fix backwards migration of pSeries guests

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@redhat.com>
(cherry picked from commit 9b45cd8fab1c7d7d07dd3ae64970b3c93b78e04c)

Conflicts:

  * src/conf/domain_conf.c:

    caused by e146264aaadf5aecf727d8c7b3d85683b55b6c48,
    which significantly refactored
    virDomainControllerDefFormat(), not being in the tree.

Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1431193

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
---
 src/conf/domain_conf.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 86415964dc..f28f6aff63 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -21670,6 +21670,23 @@ virDomainControllerDefFormat(virBufferPtr buf,
             pcihole64 = true;
         if (def->opts.pciopts.modelName != VIR_DOMAIN_CONTROLLER_PCI_MODEL_NAME_NONE)
             pciModel = true;
+        /* Historically, libvirt didn't support specifying a model name for
+         * pci-root controllers; starting from 3.6.0, however, pSeries guests
+         * use pci-root controllers with model name spapr-pci-host-bridge to
+         * represent all PHBs, including the default one.
+         *
+         * In order to allow migration of pSeries guests from older libvirt
+         * versions and back, we don't format the model name in the migratable
+         * XML if it's spapr-pci-host-bridge, thus making "no model name" and
+         * "spapr-pci-host-bridge model name" basically equivalent.
+         *
+         * The spapr-pci-host-bridge device is specific to pSeries.
+         */
+        if (def->model == VIR_DOMAIN_CONTROLLER_MODEL_PCI_ROOT &&
+            def->opts.pciopts.modelName == VIR_DOMAIN_CONTROLLER_PCI_MODEL_NAME_SPAPR_PCI_HOST_BRIDGE &&
+            flags & VIR_DOMAIN_DEF_FORMAT_MIGRATABLE) {
+            pciModel = false;
+        }
         if (def->opts.pciopts.chassisNr != -1 ||
             def->opts.pciopts.chassis != -1 ||
             def->opts.pciopts.port != -1 ||
-- 
2.13.3