qemu: Clean up qemuDomainDefaultUSBControllerModel()

Switch from the current approach, in which an initial and
likely poor default is picked and then a better one later
overwrites it, to the more common and easy to reason about
pattern where the value is returned directly as soon as
possible.

To make things easier to understand and more maintainable,
the various architectures for which we have explicit
handling are each taken care of separately, with no falling
through to the default behavior.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index f60156895a73685fdbda4ec3dfddad4be997a99d..74c393c2df04019513efa5ed9fed114c7388e872 100644 (file)
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -4320,60 +4320,76 @@ qemuDomainDefaultUSBControllerModel(const virDomainDef *def,
                                     virQEMUCaps *qemuCaps,
                                     unsigned int parseFlags)
 {
-    virDomainControllerModelUSB model = VIR_DOMAIN_CONTROLLER_MODEL_USB_DEFAULT;
+    bool abiUpdate = !!(parseFlags & VIR_DOMAIN_DEF_PARSE_ABI_UPDATE);
 
-    /* Pick a suitable default model for the USB controller if none
-     * has been selected by the user and we have the qemuCaps for
-     * figuring out which controllers are supported.
-     *
-     * We rely on device availability instead of setting the model
-     * unconditionally because, for some machine types, there's a
-     * chance we will get away with using the legacy USB controller
-     * when the relevant device is not available.
-     *
-     * See qemuBuildControllersCommandLine() */
+    if (ARCH_IS_LOONGARCH(def->os.arch)) {
+        /* Prefer qemu-xhci (USB3) */
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_QEMU_XHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_QEMU_XHCI;
 
-    /* Default USB controller is piix3-uhci if available. Fall back to
-     * 'pci-ohci' otherwise which is the default for non-x86 machines
-     * which honour -usb */
-    if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PIIX3_USB_UHCI))
-        model = VIR_DOMAIN_CONTROLLER_MODEL_USB_PIIX3_UHCI;
-    else if (!ARCH_IS_X86(def->os.arch) &&
-             virQEMUCapsGet(qemuCaps, QEMU_CAPS_PCI_OHCI))
-        model = VIR_DOMAIN_CONTROLLER_MODEL_USB_PCI_OHCI;
+        /* Allow piix3-uhci and pci-ohci (USB1) as fallback */
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PIIX3_USB_UHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_PIIX3_UHCI;
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PCI_OHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_PCI_OHCI;
+
+        return VIR_DOMAIN_CONTROLLER_MODEL_USB_DEFAULT;
+    }
+
+    if (def->os.arch == VIR_ARCH_AARCH64) {
+        /* Prefer qemu-xhci or nec-xhci (USB3) */
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_QEMU_XHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_QEMU_XHCI;
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_NEC_USB_XHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_NEC_XHCI;
+
+        /* Allow piix3-uhci and pci-ohci (USB1) as fallback */
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PIIX3_USB_UHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_PIIX3_UHCI;
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PCI_OHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_PCI_OHCI;
+
+        return VIR_DOMAIN_CONTROLLER_MODEL_USB_DEFAULT;
+    }
 
     if (ARCH_IS_S390(def->os.arch)) {
         /* No default model on s390x, one has to be provided
          * explicitly by the user */
-        model = VIR_DOMAIN_CONTROLLER_MODEL_USB_NONE;
-    } else if (ARCH_IS_PPC64(def->os.arch)) {
-        /* To not break migration we need to set default USB controller
-         * for ppc64 to pci-ohci if we cannot change ABI of the VM.
-         * The nec-usb-xhci or qemu-xhci controller is used as default
-         * only for newly defined domains or devices. */
-        if ((parseFlags & VIR_DOMAIN_DEF_PARSE_ABI_UPDATE) &&
-            virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_QEMU_XHCI)) {
-            model = VIR_DOMAIN_CONTROLLER_MODEL_USB_QEMU_XHCI;
-        } else if ((parseFlags & VIR_DOMAIN_DEF_PARSE_ABI_UPDATE) &&
-                   virQEMUCapsGet(qemuCaps, QEMU_CAPS_NEC_USB_XHCI)) {
-            model = VIR_DOMAIN_CONTROLLER_MODEL_USB_NEC_XHCI;
-        } else if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PCI_OHCI)) {
-            model = VIR_DOMAIN_CONTROLLER_MODEL_USB_PCI_OHCI;
-        } else {
-            /* Explicitly fallback to legacy USB controller for PPC64. */
-            model = VIR_DOMAIN_CONTROLLER_MODEL_USB_DEFAULT;
-        }
-    } else if (def->os.arch == VIR_ARCH_AARCH64) {
-        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_QEMU_XHCI))
-            model = VIR_DOMAIN_CONTROLLER_MODEL_USB_QEMU_XHCI;
-        else if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_NEC_USB_XHCI))
-            model = VIR_DOMAIN_CONTROLLER_MODEL_USB_NEC_XHCI;
-    } else if (ARCH_IS_LOONGARCH(def->os.arch)) {
-        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_QEMU_XHCI))
-            model = VIR_DOMAIN_CONTROLLER_MODEL_USB_QEMU_XHCI;
+        return VIR_DOMAIN_CONTROLLER_MODEL_USB_NONE;
     }
 
-    return model;
+    if (ARCH_IS_PPC64(def->os.arch)) {
+        /* Use qemu-xhci or nec-xhci (USB3) for newly-defined guests */
+        if (abiUpdate && virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_QEMU_XHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_QEMU_XHCI;
+        if (abiUpdate && virQEMUCapsGet(qemuCaps, QEMU_CAPS_NEC_USB_XHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_NEC_XHCI;
+
+        /* To preserve backwards compatibility, existing guests need to
+         * use pci-ohci (USB1) instead */
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PCI_OHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_PCI_OHCI;
+
+        return VIR_DOMAIN_CONTROLLER_MODEL_USB_DEFAULT;
+    }
+
+    if (ARCH_IS_X86(def->os.arch)) {
+        /* Use piix3-uhci (USB1) for backwards compatibility */
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PIIX3_USB_UHCI))
+            return VIR_DOMAIN_CONTROLLER_MODEL_USB_PIIX3_UHCI;
+
+        return VIR_DOMAIN_CONTROLLER_MODEL_USB_DEFAULT;
+    }
+
+    /* Most common architectures and machine types have been already
+     * handled above; for the remaining cases, use piix3-uhci or
+     * pci-ohci (USB1) as the most reasonable fallback */
+    if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PIIX3_USB_UHCI))
+        return VIR_DOMAIN_CONTROLLER_MODEL_USB_PIIX3_UHCI;
+    if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_PCI_OHCI))
+        return VIR_DOMAIN_CONTROLLER_MODEL_USB_PCI_OHCI;
+
+    return VIR_DOMAIN_CONTROLLER_MODEL_USB_DEFAULT;
 }