virQEMUCapsHasPCIMultiBus: assume true if we have no version information

In status XML, we do not store the QEMU version information, we only
format all the capabilities. We dropped QEMU_CAPS_PCI_MULTIBUS
in commit 5b783379 which was released in libvirt 3.2.0.

Therefore the only way of telling if the already running domain
at the time of daemon restart has been started with a QEMU that does
use 'pci.0' or not on PPC is to look at the pci-root controller's
alias. This is not an option if the domain has a user-specified alias
for the pci-root.

Instead of reintroducing the capability, assume 'pci.0' when we have
no version information. That way the only left broken use case would
be the combination of user aliases and very old QEMU.

Partially reverts commit 3a37af1e4.

https://bugzilla.redhat.com/show_bug.cgi?id=1518148

src/qemu/qemu_capabilities.c

@@ -2436,6 +2436,14 @@ bool virQEMUCapsHasPCIMultiBus(virQEMUCapsPtr qemuCaps,
          *     ppce500: 1.6.0
          */
 
+        /* We do not store the qemu version in domain status XML.
+         * Hope the user is using a QEMU new enough to use 'pci.0',
+         * otherwise the results of this function will be wrong
+         * for domains already running at the time of daemon
+         * restart */
+        if (qemuCaps->version == 0)
+            return true;
+
         if (qemuCaps->version >= 2000000)
             return true;
 
@@ -2487,14 +2495,6 @@ virArch virQEMUCapsGetArch(virQEMUCapsPtr qemuCaps)
 }
 
 
-void
-virQEMUCapsSetVersion(virQEMUCapsPtr qemuCaps,
-                      unsigned int version)
-{
-    qemuCaps->version = version;
-}
-
-
 unsigned int virQEMUCapsGetVersion(virQEMUCapsPtr qemuCaps)
 {
     return qemuCaps->version;

src/qemu/qemu_capspriv.h

@@ -55,10 +55,6 @@ void
 virQEMUCapsSetArch(virQEMUCapsPtr qemuCaps,
                    virArch arch);
 
-void
-virQEMUCapsSetVersion(virQEMUCapsPtr qemuCaps,
-                      unsigned int version);
-
 void
 virQEMUCapsInitHostCPUModel(virQEMUCapsPtr qemuCaps,
                             virArch hostArch,

tests/qemuxml2argvtest.c

@@ -384,11 +384,6 @@ testUpdateQEMUCaps(const struct testInfo *info,
 
     virQEMUCapsInitQMPBasicArch(info->qemuCaps);
 
-    /* We need to pretend QEMU 2.0.0 is in use so that pSeries guests
-     * will get the correct alias assigned to their buses.
-     * See virQEMUCapsHasPCIMultiBus() */
-    virQEMUCapsSetVersion(info->qemuCaps, 2000000);
-
     if (testAddCPUModels(info->qemuCaps, info->skipLegacyCPUs) < 0)
         goto cleanup;