[PATCH] net/virtio-user: fix cannot get initialized

[Jianfeng Tan <jianfeng.tan@intel.com>]

After the introduction of vhost MTU, VIRTIO_NET_F_MTU is enabled
by default. However, virtio-user vtpci does not support to get
MTU from device yet, i.e., vtpci_read_dev_config(MTU) fails.
Plus, struct virtio_net_config is defined as a uninitialized
variable, and could be different values in
virtio_negotiate_features() and virtio_init_device().

In some cases, it passes the check in virtio_negotiate_features()
but fails the check in virtio_init_device(). As a result,
virtio-user canno be initialized.

To fix it, (1) accessing uninitialized variable is not a good
practice, so initialize it as zero; (2) explicitly disable MTU
feature in virtio-user.

Fixes: 49d26d9e3f47 ("net/virtio: support MTU feature")
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>

Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
---
 drivers/net/virtio/virtio_ethdev.c               | 4 ++--
 drivers/net/virtio/virtio_user/virtio_user_dev.c | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
index 78cb3e8..4c43784 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -1163,7 +1163,7 @@ virtio_negotiate_features(struct virtio_hw *hw, uint64_t req_features)
 
 	/* If supported, ensure MTU value is valid before acknowledging it. */
 	if (host_features & req_features & (1ULL << VIRTIO_NET_F_MTU)) {
-		struct virtio_net_config config;
+		struct virtio_net_config config = {0};
 
 		vtpci_read_dev_config(hw,
 			offsetof(struct virtio_net_config, mtu),
@@ -1332,7 +1332,7 @@ virtio_init_device(struct rte_eth_dev *eth_dev, uint64_t req_features)
 {
 	struct virtio_hw *hw = eth_dev->data->dev_private;
 	struct virtio_net_config *config;
-	struct virtio_net_config local_config;
+	struct virtio_net_config local_config = {0};
 	struct rte_pci_device *pci_dev = NULL;
 	int ret;
 
diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c b/drivers/net/virtio/virtio_user/virtio_user_dev.c
index 6871cd4..529b3d7 100644
--- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
+++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c
@@ -362,6 +362,12 @@ virtio_user_dev_init(struct virtio_user_dev *dev, char *path, int queues,
 	/* The backend will not report this feature, we add it explicitly */
 	dev->device_features |= (1ull << VIRTIO_NET_F_STATUS);
 
+	/* TODO: VIRTIO_NET_F_MTU is for QEMU to advertise MTU to both frontend
+	 * and backend driver. For virtio-user, disable it for now, until we
+	 * have a parameter to specify the MTU.
+	 */
+	dev->device_features &= ~(1ull << VIRTIO_NET_F_MTU);
+
 	return 0;
 }
 
-- 
2.7.4