• Michael S. Tsirkin's avatar
    tun: only queue packets on device · 5d097109
    Michael S. Tsirkin authored
    Historically tun supported two modes of operation:
    - in default mode, a small number of packets would get queued
      at the device, the rest would be queued in qdisc
    - in one queue mode, all packets would get queued at the device
    
    This might have made sense up to a point where we made the
    queue depth for both modes the same and set it to
    a huge value (500) so unless the consumer
    is stuck the chance of losing packets is small.
    
    Thus in practice both modes behave the same, but the
    default mode has some problems:
    - if packets are never consumed, fragments are never orphaned
      which cases a DOS for sender using zero copy transmit
    - overrun errors are hard to diagnose: fifo error is incremented
      only once so you can not distinguish between
      userspace that is stuck and a transient failure,
      tcpdump on the device does not show any traffic
    
    Userspace solves this simply by enabling IFF_ONE_QUEUE
    but there seems to be little point in not doing the
    right thing for everyone, by default.
    Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    5d097109
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