[Qemu-devel] [PATCH 2/2] virtio-net: do not expose a larger config size if multiqueue isn't enabled

[Anthony Liguori]

The windows PV drivers seem to get very upset if the config size changes.
Even when we disable features, we don't change the config size today which
is a bug.

This patch is a pretty rough way to solve this problem and it only handles
the multiqueue case specifically.

Cc: Michael Tokarev <m...@tls.msk.ru>
Reported-by: Michael Tokarev <m...@tls.msk.ru>
Signed-off-by: Anthony Liguori <aligu...@us.ibm.com>
---
 hw/virtio-net.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index e37358a..8d15813 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -73,6 +73,7 @@ typedef struct VirtIONet
     int multiqueue;
     uint16_t max_queues;
     uint16_t curr_queues;
+    int config_size;
 } VirtIONet;
 
 static VirtIONetQueue *virtio_net_get_subqueue(NetClientState *nc)
@@ -99,20 +100,20 @@ static VirtIONet *to_virtio_net(VirtIODevice *vdev)
 static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
 {
     VirtIONet *n = to_virtio_net(vdev);
-    struct virtio_net_config netcfg;
+    struct virtio_net_config netcfg = {};
 
     stw_p(&netcfg.status, n->status);
     stw_p(&netcfg.max_virtqueue_pairs, n->max_queues);
     memcpy(netcfg.mac, n->mac, ETH_ALEN);
-    memcpy(config, &netcfg, sizeof(netcfg));
+    memcpy(config, &netcfg, n->config_size);
 }
 
 static void virtio_net_set_config(VirtIODevice *vdev, const uint8_t *config)
 {
     VirtIONet *n = to_virtio_net(vdev);
-    struct virtio_net_config netcfg;
+    struct virtio_net_config netcfg = {};
 
-    memcpy(&netcfg, config, sizeof(netcfg));
+    memcpy(&netcfg, config, n->config_size);
 
     if (!(n->vdev.guest_features >> VIRTIO_NET_F_CTRL_MAC_ADDR & 1) &&
         memcmp(netcfg.mac, n->mac, ETH_ALEN)) {
@@ -1279,14 +1280,21 @@ static void virtio_net_guest_notifier_mask(VirtIODevice 
*vdev, int idx,
 }
 
 VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf,
-                              virtio_net_conf *net)
+                              virtio_net_conf *net, uint32_t host_features)
 {
     VirtIONet *n;
     int i;
+    int config_size;
 
+    if (host_features & VIRTIO_NET_F_MQ) {
+        config_size = sizeof(struct virtio_net_config);
+    } else {
+        config_size = 8;
+    }
     n = (VirtIONet *)virtio_common_init("virtio-net", VIRTIO_ID_NET,
-                                        sizeof(struct virtio_net_config),
+                                        config_size,
                                         sizeof(VirtIONet));
+    n->config_size = config_size;
 
     n->vdev.get_config = virtio_net_get_config;
     n->vdev.set_config = virtio_net_set_config;
-- 
1.8.0