[PATCH] virtio_net: Warn if insufficient queue length for transmitting

[Darius Rad <darius@bluespec.com>]

The transmit queue is stopped when the number of free queue entries is less
than 2+MAX_SKB_FRAGS, in start_xmit().  If the queue length (QUEUE_NUM_MAX)
is less than then this, transmission will immediately trigger a netdev
watchdog timeout.  Report this condition earlier and more directly.

Signed-off-by: Darius Rad <darius@bluespec.com>
---
 drivers/net/virtio_net.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 115c3c5414f2..72ee8473b61c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -4917,6 +4917,9 @@ static int virtnet_probe(struct virtio_device *vdev)
 			set_bit(guest_offloads[i], &vi->guest_offloads);
 	vi->guest_offloads_capable = vi->guest_offloads;
 
+	if (virtqueue_get_vring_size(vi->sq->vq) < 2 + MAX_SKB_FRAGS)
+		netdev_warn_once(dev, "not enough queue entries, expect xmit timeout\n");
+
 	pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
 		 dev->name, max_queue_pairs);
 
-- 
2.39.2