[Qemu-devel] [PATCHv2 2/2] virtio-net: work around for windows driver bug

[Michael S. Tsirkin]

Windows drivers from 22 Jan 2013 and older fail when config size != 32,
which was the size before max_virtqueue_pairs was added.
Force config size to a value these drivers expect to avoid
breakage unless we really need max_virtqueue_pairs.

Signed-off-by: Michael S. Tsirkin <address@hidden>
---
 hw/virtio-net.c | 15 ++++++++++++---
 hw/virtio-net.h |  6 +++++-
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index 510a0f6..2464cd5 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -1287,9 +1287,18 @@ VirtIODevice *virtio_net_init(DeviceState *dev, NICConf 
*conf,
 {
     VirtIONet *n;
     int i;
-
-    n = (VirtIONet *)virtio_common_init("virtio-net", VIRTIO_ID_NET,
-                                        sizeof(struct virtio_net_config),
+    size_t config_size;
+
+    /*
+     * Windows drivers from 22 Jan 2013 and older fail when config size != 32,
+     * which was the size before max_virtqueue_pairs was added.
+     * Force config size to a value these drivers expect to avoid
+     * breakage unless we really need max_virtqueue_pairs.
+     */
+    config_size = conf->queues > 1 ?  sizeof(struct virtio_net_config) :
+        offsetof(struct virtio_net_config, max_virtqueue_pairs);
+
+    n = (VirtIONet *)virtio_common_init("virtio-net", VIRTIO_ID_NET, 
config_size,
                                         sizeof(VirtIONet));
 
     n->vdev.get_config = virtio_net_get_config;
diff --git a/hw/virtio-net.h b/hw/virtio-net.h
index 414365d..799b2ca 100644
--- a/hw/virtio-net.h
+++ b/hw/virtio-net.h
@@ -75,7 +75,11 @@ struct virtio_net_config
     uint8_t mac[ETH_ALEN];
     /* See VIRTIO_NET_F_STATUS and VIRTIO_NET_S_* above */
     uint16_t status;
-    /* Max virtqueue pairs supported by the device */
+    /*
+     * Fields below need special handling because of driver bugs.
+     * See virtio_net_init.
+     * Max virtqueue pairs supported by the device.
+     */ 
     uint16_t max_virtqueue_pairs;
 } QEMU_PACKED;
 
-- 
MST