[Qemu-devel] [PATCH 3/4] net/virtio: add failover support

[Jens Freimann]

This patch adds support to handle failover device pairs of a virtio-net
device and a vfio-pci device, where the virtio-net acts as the standby
device and the vfio-pci device as the primary.

The general idea is that we have a pair of devices, a vfio-pci and a
emulated (virtio-net) device. Before migration the vfio device is
unplugged and data flows to the emulated device, on the target side
another vfio-pci device is plugged in to take over the data-path. In the
guest the net_failover module will pair net devices with the same MAC
address.

To achieve this we need:

1. Provide a callback function for the should_be_hidden DeviceListener.
   It is called when the primary device is plugged in. Evaluate the QOpt
   passed in to check if it is the matching primary device. It returns
   two values:
     - one to signal if the device to be added is the matching
       primary device
     - another one to signal to qdev if it should actually
       continue with adding the device or skip it.

   In the latter case it stores the device options in the VirtioNet
   struct and the device is added once the VIRTIO_NET_F_STANDBY feature is
   negotiated during virtio feature negotiation.

2. Register a callback for migration status notifier. When called it
   will unplug its primary device before the migration happens.

Signed-off-by: Jens Freimann <address@hidden>
---
 hw/net/virtio-net.c            | 117 +++++++++++++++++++++++++++++++++
 include/hw/virtio/virtio-net.h |  12 ++++
 2 files changed, 129 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index ffe0872fff..120eccbb98 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -12,6 +12,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/atomic.h"
 #include "qemu/iov.h"
 #include "hw/virtio/virtio.h"
 #include "net/net.h"
@@ -19,6 +20,10 @@
 #include "net/tap.h"
 #include "qemu/error-report.h"
 #include "qemu/timer.h"
+#include "qemu/option.h"
+#include "qemu/option_int.h"
+#include "qemu/config-file.h"
+#include "qapi/qmp/qdict.h"
 #include "hw/virtio/virtio-net.h"
 #include "net/vhost_net.h"
 #include "net/announce.h"
@@ -29,6 +34,8 @@
 #include "migration/misc.h"
 #include "standard-headers/linux/ethtool.h"
 #include "trace.h"
+#include "monitor/qdev.h"
+#include "hw/pci/pci.h"
 
 #define VIRTIO_NET_VM_VERSION    11
 
@@ -364,6 +371,9 @@ static void virtio_net_set_status(struct VirtIODevice 
*vdev, uint8_t status)
     }
 }
 
+
+static void virtio_net_primary_plug_timer(void *opaque);
+
 static void virtio_net_set_link_status(NetClientState *nc)
 {
     VirtIONet *n = qemu_get_nic_opaque(nc);
@@ -786,6 +796,14 @@ static void virtio_net_set_features(VirtIODevice *vdev, 
uint64_t features)
     } else {
         memset(n->vlans, 0xff, MAX_VLAN >> 3);
     }
+
+    if (virtio_has_feature(features, VIRTIO_NET_F_STANDBY)) {
+        atomic_set(&n->primary_should_be_hidden, false);
+        if (n->primary_device_timer)
+            timer_mod(n->primary_device_timer,
+                qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) +
+                4000);
+    }
 }
 
 static int virtio_net_handle_rx_mode(VirtIONet *n, uint8_t cmd,
@@ -2626,6 +2644,87 @@ void virtio_net_set_netclient_name(VirtIONet *n, const 
char *name,
     n->netclient_type = g_strdup(type);
 }
 
+static void virtio_net_primary_plug_timer(void *opaque)
+{
+    VirtIONet *n = opaque;
+    Error *err = NULL;
+
+    if (n->primary_device_dict)
+        n->primary_device_opts = qemu_opts_from_qdict(qemu_find_opts("device"),
+            n->primary_device_dict, &err);
+    if (n->primary_device_opts) {
+        n->primary_dev = qdev_device_add(n->primary_device_opts, &err);
+        error_setg(&err, "virtio_net: couldn't plug in primary device");
+        return;
+    }
+    if (!n->primary_device_dict && err) {
+        if (n->primary_device_timer) {
+            timer_mod(n->primary_device_timer,
+                qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) +
+                100);
+        }
+    }
+}
+
+static void virtio_net_handle_migration_primary(VirtIONet *n,
+                                                MigrationState *s)
+{
+    Error *err = NULL;
+    bool should_be_hidden = atomic_read(&n->primary_should_be_hidden);
+
+    n->primary_dev = qdev_find_recursive(sysbus_get_default(),
+            n->primary_device_id);
+    if (!n->primary_dev) {
+        error_setg(&err, "virtio_net: couldn't find primary device");
+    }
+    if (migration_in_setup(s) && !should_be_hidden && n->primary_dev) {
+        qdev_unplug(n->primary_dev, &err);
+        if (!err) {
+            atomic_set(&n->primary_should_be_hidden, true);
+            n->primary_dev = NULL;
+        }
+    } else if (migration_has_failed(s)) {
+        if (should_be_hidden && !n->primary_dev) {
+            /* We already unplugged the device let's plugged it back */
+            n->primary_dev = qdev_device_add(n->primary_device_opts, &err);
+        }
+    }
+}
+
+static void migration_state_notifier(Notifier *notifier, void *data)
+{
+    MigrationState *s = data;
+    VirtIONet *n = container_of(notifier, VirtIONet, migration_state);
+    virtio_net_handle_migration_primary(n, s);
+}
+
+static void virtio_net_primary_should_be_hidden(DeviceListener *listener,
+            QemuOpts *device_opts, bool *match_found, bool *res)
+{
+    VirtIONet *n = container_of(listener, VirtIONet, primary_listener);
+
+    if (device_opts) {
+        n->primary_device_dict = qemu_opts_to_qdict(device_opts,
+                n->primary_device_dict);
+    }
+    g_free(n->standby_id);
+    n->standby_id = g_strdup(qdict_get_try_str(n->primary_device_dict,
+                             "standby"));
+    if (n->standby_id) {
+        *match_found = true;
+    }
+    /* primary_should_be_hidden is set during feature negotiation */
+    if (atomic_read(&n->primary_should_be_hidden) && *match_found) {
+        *res = true;
+    } else if (*match_found)  {
+        n->primary_device_dict = qemu_opts_to_qdict(device_opts,
+                n->primary_device_dict);
+        *res = false;
+    }
+    g_free(n->primary_device_id);
+    n->primary_device_id = g_strdup(device_opts->id);
+}
+
 static void virtio_net_device_realize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
@@ -2656,6 +2755,18 @@ static void virtio_net_device_realize(DeviceState *dev, 
Error **errp)
         n->host_features |= (1ULL << VIRTIO_NET_F_SPEED_DUPLEX);
     }
 
+    if (n->failover) {
+        n->primary_listener.should_be_hidden =
+            virtio_net_primary_should_be_hidden;
+        atomic_set(&n->primary_should_be_hidden, true);
+        device_listener_register(&n->primary_listener);
+        n->migration_state.notify = migration_state_notifier;
+        add_migration_state_change_notifier(&n->migration_state);
+        n->host_features |= (1ULL << VIRTIO_NET_F_STANDBY);
+        n->primary_device_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL,
+                                     virtio_net_primary_plug_timer, n);
+    }
+
     virtio_net_set_config_size(n, n->host_features);
     virtio_init(vdev, "virtio-net", VIRTIO_ID_NET, n->config_size);
 
@@ -2778,6 +2889,11 @@ static void virtio_net_device_unrealize(DeviceState 
*dev, Error **errp)
     g_free(n->mac_table.macs);
     g_free(n->vlans);
 
+    g_free(n->primary_device_id);
+    g_free(n->standby_id);
+    qobject_unref(n->primary_device_dict);
+    n->primary_device_dict = NULL;
+
     max_queues = n->multiqueue ? n->max_queues : 1;
     for (i = 0; i < max_queues; i++) {
         virtio_net_del_queue(n, i);
@@ -2885,6 +3001,7 @@ static Property virtio_net_properties[] = {
                      true),
     DEFINE_PROP_INT32("speed", VirtIONet, net_conf.speed, SPEED_UNKNOWN),
     DEFINE_PROP_STRING("duplex", VirtIONet, net_conf.duplex_str),
+    DEFINE_PROP_BOOL("failover", VirtIONet, failover, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index b96f0c643f..c2bb6ada44 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -18,6 +18,7 @@
 #include "standard-headers/linux/virtio_net.h"
 #include "hw/virtio/virtio.h"
 #include "net/announce.h"
+#include "qemu/option_int.h"
 
 #define TYPE_VIRTIO_NET "virtio-net-device"
 #define VIRTIO_NET(obj) \
@@ -43,6 +44,7 @@ typedef struct virtio_net_conf
     int32_t speed;
     char *duplex_str;
     uint8_t duplex;
+    char *primary_id_str;
 } virtio_net_conf;
 
 /* Coalesced packets type & status */
@@ -185,6 +187,16 @@ struct VirtIONet {
     AnnounceTimer announce_timer;
     bool needs_vnet_hdr_swap;
     bool mtu_bypass_backend;
+    QemuOpts *primary_device_opts;
+    QDict *primary_device_dict;
+    DeviceState *primary_dev;
+    char *primary_device_id;
+    char *standby_id;
+    bool primary_should_be_hidden;
+    bool failover;
+    DeviceListener primary_listener;
+    QEMUTimer *primary_device_timer;
+    Notifier migration_state;
 };
 
 void virtio_net_set_netclient_name(VirtIONet *n, const char *name,
-- 
2.21.0