xen-netfront: always set num queues if possible

If netfront connects with two (or more) queues and then reconnects with
only one queue it fails to delete or rewrite the multi-queue-num-queues
key and netback will try to use the wrong number of queues.

Always write the num-queues field if the backend has multi-queue support.

Signed-off-by: Chas Williams <3chas3@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 7 deletions

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index f821a97d7827..9bf63c27a9b7 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1819,19 +1819,22 @@ again:
                 goto destroy_ring;
         }
 
-        if (num_queues == 1) {
-                err = write_queue_xenstore_keys(&info->queues[0], &xbt, 0); /* flat */
-                if (err)
-                        goto abort_transaction_no_dev_fatal;
-        } else {
+        if (xenbus_exists(XBT_NIL,
+                          info->xbdev->otherend, "multi-queue-max-queues")) {
                 /* Write the number of queues */
-                err = xenbus_printf(xbt, dev->nodename, "multi-queue-num-queues",
-                                    "%u", num_queues);
+                err = xenbus_printf(xbt, dev->nodename,
+                                    "multi-queue-num-queues", "%u", num_queues);
                 if (err) {
                         message = "writing multi-queue-num-queues";
                         goto abort_transaction_no_dev_fatal;
                 }
+        }
 
+        if (num_queues == 1) {
+                err = write_queue_xenstore_keys(&info->queues[0], &xbt, 0); /* flat */
+                if (err)
+                        goto abort_transaction_no_dev_fatal;
+        } else {
                 /* Write the keys for each queue */
                 for (i = 0; i < num_queues; ++i) {
                         queue = &info->queues[i];