netdev-afxdp: Fix use of unconfigured device.

In case of failure of 'xsk_configure_all()', 'n_rxq' and 'xdpmode'
will remain in a new state. This will result in successful
reconfiguration (immediate return, because configuration is already
applied) if 'netdev_reconfigure()' will be called again.

Same issue was fixed previously for netdev-dpdk using 'dev->started'
flag in commit:
606f665072 ("netdev-dpdk: Don't use PMD driver if not configured successfully")

Let's use similar approach with checking the 'dev->xsks' which only
exists if configuration was successful.

Additionally implemented 'netdev_afxdp_construct()' function to
explicitly initialize all the specific fields and request the
reconfiguration.

CC: William Tu <u9012063@gmail.com>
Fixes: 0de1b42596 ("netdev-afxdp: add new netdev type for AF_XDP.")
Acked-by: William Tu <u9012063@gmail.com>
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>

lib/netdev-afxdp.c

@@ -525,7 +525,8 @@ netdev_afxdp_reconfigure(struct netdev *netdev)
     ovs_mutex_lock(&dev->mutex);
 
     if (netdev->n_rxq == dev->requested_n_rxq
-        && dev->xdpmode == dev->requested_xdpmode) {
+        && dev->xdpmode == dev->requested_xdpmode
+        && dev->xsks) {
         goto out;
     }
 
@@ -965,6 +966,33 @@ netdev_afxdp_rxq_destruct(struct netdev_rxq *rxq_ OVS_UNUSED)
     /* Nothing. */
 }
 
+int
+netdev_afxdp_construct(struct netdev *netdev)
+{
+    struct netdev_linux *dev = netdev_linux_cast(netdev);
+    int ret;
+
+    /* Configure common netdev-linux first. */
+    ret = netdev_linux_construct(netdev);
+    if (ret) {
+        return ret;
+    }
+
+    /* Queues should not be used before the first reconfiguration. Clearing. */
+    netdev->n_rxq = 0;
+    netdev->n_txq = 0;
+    dev->xdpmode = 0;
+
+    dev->requested_n_rxq = NR_QUEUE;
+    dev->requested_xdpmode = XDP_COPY;
+
+    dev->xsks = NULL;
+    dev->tx_locks = NULL;
+
+    netdev_request_reconfigure(netdev);
+    return 0;
+}
+
 void
 netdev_afxdp_destruct(struct netdev *netdev)
 {

lib/netdev-afxdp.h

@@ -36,6 +36,7 @@ struct netdev_stats;
 
 int netdev_afxdp_rxq_construct(struct netdev_rxq *rxq_);
 void netdev_afxdp_rxq_destruct(struct netdev_rxq *rxq_);
+int netdev_afxdp_construct(struct netdev *netdev_);
 void netdev_afxdp_destruct(struct netdev *netdev_);
 
 int netdev_afxdp_rxq_recv(struct netdev_rxq *rxq_,

lib/netdev-linux-private.h

@@ -43,6 +43,7 @@ struct netdev_rxq_linux {
     int fd;
 };
 
+int netdev_linux_construct(struct netdev *);
 void netdev_linux_run(const struct netdev_class *);
 
 int get_stats_via_netlink(const struct netdev *netdev_,

lib/netdev-linux.c

@@ -906,7 +906,7 @@ netdev_linux_common_construct(struct netdev *netdev_)
 }
 
 /* Creates system and internal devices. */
-static int
+int
 netdev_linux_construct(struct netdev *netdev_)
 {
     struct netdev_linux *netdev = netdev_linux_cast(netdev_);
@@ -3290,7 +3290,7 @@ const struct netdev_class netdev_afxdp_class = {
     NETDEV_LINUX_CLASS_COMMON,
     .type = "afxdp",
     .is_pmd = true,
-    .construct = netdev_linux_construct,
+    .construct = netdev_afxdp_construct,
     .destruct = netdev_afxdp_destruct,
     .get_stats = netdev_afxdp_get_stats,
     .get_status = netdev_linux_get_status,