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Jesper Dangaard Brouer authored
It is a clear misconfiguration to attach a qdisc to a device with tx_queue_len zero, because some qdisc's (namely, pfifo, bfifo, gred, htb, plug and sfb) inherit/copy this value as their queue length. Why should the kernel catch such a misconfiguration? Because prior to introducing the IFF_NO_QUEUE device flag, userspace found a loophole in the qdisc config system that allowed them to achieve the equivalent of IFF_NO_QUEUE, which is to remove the qdisc code path entirely from a device. The loophole on older kernels is setting tx_queue_len=0, *prior* to device qdisc init (the config time is significant, simply setting tx_queue_len=0 doesn't trigger the loophole). This loophole is currently used by Docker[1] to get better performance and scalability out of the veth device. The Docker developers were warned[1] that they needed to adjust the tx_queue_len if ever attaching a qdisc. The OpenShift project didn't remember this warning and attached a qdisc, this were caught and fixed in[2]. [1] https://github.com/docker/libcontainer/pull/193 [2] https://github.com/openshift/origin/pull/11126 Instead of fixing every userspace program that used this loophole, and forgot to reset the tx_queue_len, prior to attaching a qdisc. Let's catch the misconfiguration on the kernel side. Signed-off-by:
Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by:
David S. Miller <davem@davemloft.net>
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