qemu_domain: Strip <acpi/> from s390(x) definitions

The s390(x) machines never supported ACPI. That didn't stop users
enabling ACPI in their config. As of libvirt-9.2 (98c4e3d073) with new
enough qemu we reject configs which require ACPI, but qemu can't satisfy
it.

This breaks migration of existing VMs with the old wrong configs to new
libvirt installations.

To address this introduce a post-parse fixup removing the ACPI flag
specifically for s390 machines which do enable it in the definition.

The advantage of doing it in post-parse, rather than simply relaxing the
ABI stability check to allow users providing an fixed XML when migrating
(allowing change of the ACPI flag for s390 in ABI stability check, as it
 doesn't impact ABI), is that only the destination installation needs to
be patched in order to preserve migration.

To mitigate the disadvantage of simply stripping it from all s390(x)
configs the hack is not applied when defining or starting a new domain
from the XML, to preserve the error about unsupported configuration.

Resolves: https://issues.redhat.com/browse/RHEL-49516
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Boris Fiuczynski <fiuczy@linux.ibm.com>

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 198ab99aefa75b758e6adc76fa5e96d13888fd33..1e355f0f41344780c951813ac89873b348ca8a02 100644 (file)
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -5020,6 +5020,53 @@ qemuDomainDefPostParseBasic(virDomainDef *def,
 }
 
 
+/**
+ * qemuDomainDefACPIPostParse:
+ * @def: domain definition
+ * @qemuCaps: qemu capabilities object
+ *
+ * Fixup the use of ACPI flag on certain architectures that never supported it
+ * and users for some reason used it, which would break migration to newer
+ * libvirt versions which check whether given machine type supports ACPI.
+ *
+ * The fixup is done in post-parse as it's hard to update the ABI stability
+ * check on source of the migration.
+ */
+static void
+qemuDomainDefACPIPostParse(virDomainDef *def,
+                           virQEMUCaps *qemuCaps,
+                           unsigned int parseFlags)
+{
+    /* Only cases when ACPI is enabled need to be fixed up */
+    if (def->features[VIR_DOMAIN_FEATURE_ACPI] != VIR_TRISTATE_SWITCH_ON)
+        return;
+
+    /* Strip the <acpi/> feature only for non-fresh configs, in order to still
+     * produce an error if the feature is present in a newly defined one.
+     *
+     * The use of the VIR_DOMAIN_DEF_PARSE_ABI_UPDATE looks counter-intuitive,
+     * but it's used only in qemuDomainCreateXML/qemuDomainDefineXMLFlags APIs
+     * */
+    if (parseFlags & VIR_DOMAIN_DEF_PARSE_ABI_UPDATE)
+        return;
+
+    /* This fixup is applicable _only_ on architectures which were present as of
+     * libvirt-9.2 and *never* supported ACPI. The fixup is currently done only
+     * for existing users of s390(x) to fix migration for configs which had
+     * <acpi/> despite being ignored.
+     */
+    if (def->os.arch != VIR_ARCH_S390 &&
+        def->os.arch != VIR_ARCH_S390X)
+        return;
+
+    /* To be sure, we only strip ACPI if given machine type doesn't support it */
+    if (virQEMUCapsMachineSupportsACPI(qemuCaps, def->virtType, def->os.machine) != VIR_TRISTATE_BOOL_NO)
+        return;
+
+    def->features[VIR_DOMAIN_FEATURE_ACPI] = VIR_TRISTATE_SWITCH_ABSENT;
+}
+
+
 static int
 qemuDomainDefPostParse(virDomainDef *def,
                        unsigned int parseFlags,
@@ -5040,6 +5087,8 @@ qemuDomainDefPostParse(virDomainDef *def,
     if (qemuDomainDefMachinePostParse(def, qemuCaps) < 0)
         return -1;
 
+    qemuDomainDefACPIPostParse(def, qemuCaps, parseFlags);
+
     if (qemuDomainDefBootPostParse(def, driver, parseFlags) < 0)
         return -1;