net eth1: Unexpected TX queue failure: -28 って何だろう、という話 ref: http://qiita.com/twainy@github/items/7ca23e658f37e9cecfe2

errno-base.h#31

#define ENOSPC      28  /* No space left on device */

file0.txt

$ dmesg | tail -1
[16276010.045007] net eth1: Unexpected TX queue failure: -28

file6.txt

ifconfig ${interface} txqueuelen ${size}
ifconfig eth1 txqueuelen 10000
ifconfig eth0 txqueuelen 5000

virtio_net.c

static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
{
    struct virtnet_info *vi = netdev_priv(dev);
    int capacity;

    /* Free up any pending old buffers before queueing new ones. */
    free_old_xmit_skbs(vi);

    /* Try to transmit */
    capacity = xmit_skb(vi, skb);

    /* This can happen with OOM and indirect buffers. */
    if (unlikely(capacity < 0)) {
        if (likely(capacity == -ENOMEM)) {
            if (net_ratelimit())
                dev_warn(&dev->dev,
                     "TX queue failure: out of memory\n");
        } else {
            dev->stats.tx_fifo_errors++;
            if (net_ratelimit())
                dev_warn(&dev->dev,
                     "Unexpected TX queue failure: %d\n",
                     capacity);
        }
        dev->stats.tx_dropped++;
        kfree_skb(skb);
        return NETDEV_TX_OK;
    }

.......................
}

virtio_net.c#xmit_skb

static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
{
......................
    return virtqueue_add_buf(vi->svq, vi->tx_sg, hdr->num_sg,
                 0, skb, GFP_ATOMIC);
}

virtio_ring.c#191

int virtqueue_add_buf(struct virtqueue *_vq,
              struct scatterlist sg[],
              unsigned int out,
              unsigned int in,
              void *data,
              gfp_t gfp)
{
    struct vring_virtqueue *vq = to_vvq(_vq);
    unsigned int i, avail, uninitialized_var(prev);
    int head;

....................
    if (vq->num_free < out + in) {
        pr_debug("Can't add buf len %i - avail = %i\n",
             out + in, vq->num_free);
        /* FIXME: for historical reasons, we force a notify here if
         * there are outgoing parts to the buffer.  Presumably the
         * host should service the ring ASAP. */
        if (out)
            vq->notify(&vq->vq);
        END_USE(vq);
        return -ENOSPC;
    }
....................
}

virtio_ring.c#77

/* Number of free buffers */
unsigned int num_free;