pci: add option for net failover

This patch adds a failover_pair_id property to PCIDev which is
used to link the primary device in a failover pair (the PCI dev) to
a standby (a virtio-net-pci) device.

It only supports ethernet devices. Also currently it only supports
PCIe devices. The requirement for PCIe is because it doesn't support
other hotplug controllers at the moment. The failover functionality can
be added to other hotplug controllers like ACPI, SHCP,... later on.

Signed-off-by: Jens Freimann <jfreimann@redhat.com>
Message-Id: <20191029114905.6856-3-jfreimann@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci/pci.c

@@ -75,6 +75,8 @@ static Property pci_props[] = {
                     QEMU_PCIE_LNKSTA_DLLLA_BITNR, true),
     DEFINE_PROP_BIT("x-pcie-extcap-init", PCIDevice, cap_present,
                     QEMU_PCIE_EXTCAP_INIT_BITNR, true),
+    DEFINE_PROP_STRING("failover_pair_id", PCIDevice,
+                       failover_pair_id),
     DEFINE_PROP_END_OF_LIST()
 };
 
@@ -2077,6 +2079,7 @@ static void pci_qdev_realize(DeviceState *qdev, Error **errp)
     ObjectClass *klass = OBJECT_CLASS(pc);
     Error *local_err = NULL;
     bool is_default_rom;
+    uint16_t class_id;
 
     /* initialize cap_present for pci_is_express() and pci_config_size(),
      * Note that hybrid PCIs are not set automatically and need to manage
@@ -2101,6 +2104,34 @@ static void pci_qdev_realize(DeviceState *qdev, Error **errp)
         }
     }
 
+    if (pci_dev->failover_pair_id) {
+        if (!pci_bus_is_express(pci_get_bus(pci_dev))) {
+            error_setg(errp, "failover primary device must be on "
+                             "PCIExpress bus");
+            error_propagate(errp, local_err);
+            pci_qdev_unrealize(DEVICE(pci_dev), NULL);
+            return;
+        }
+        class_id = pci_get_word(pci_dev->config + PCI_CLASS_DEVICE);
+        if (class_id != PCI_CLASS_NETWORK_ETHERNET) {
+            error_setg(errp, "failover primary device is not an "
+                             "Ethernet device");
+            error_propagate(errp, local_err);
+            pci_qdev_unrealize(DEVICE(pci_dev), NULL);
+            return;
+        }
+        if (!(pci_dev->cap_present & QEMU_PCI_CAP_MULTIFUNCTION)
+            && (PCI_FUNC(pci_dev->devfn) == 0)) {
+            qdev->allow_unplug_during_migration = true;
+        } else {
+            error_setg(errp, "failover: primary device must be in its own "
+                              "PCI slot");
+            error_propagate(errp, local_err);
+            pci_qdev_unrealize(DEVICE(pci_dev), NULL);
+            return;
+        }
+    }
+
     /* rom loading */
     is_default_rom = false;
     if (pci_dev->romfile == NULL && pc->romfile != NULL) {

include/hw/pci/pci.h

@@ -352,6 +352,9 @@ struct PCIDevice {
     MSIVectorUseNotifier msix_vector_use_notifier;
     MSIVectorReleaseNotifier msix_vector_release_notifier;
     MSIVectorPollNotifier msix_vector_poll_notifier;
+
+    /* ID of standby device in net_failover pair */
+    char *failover_pair_id;
 };
 
 void pci_register_bar(PCIDevice *pci_dev, int region_num,