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    SubjectRe: [PATCH net-next 0/2] virtio-net: re enable XDP_REDIRECT for mergeable buffer
    On Thu,  1 Mar 2018 11:19:03 +0800
    Jason Wang <jasowang@redhat.com> wrote:

    > This series tries to re-enable XDP_REDIRECT for mergeable buffer which
    > was removed since commit 7324f5399b06 ("virtio_net: disable
    > XDP_REDIRECT in receive_mergeable() case"). Main concerns are:
    >
    > - not enough tailroom was reserved which breaks cpumap

    To address this at a more fundamental level, I would suggest that we/you
    instead extend XDP to know it's buffers "frame" size/end. (The
    assumption use to be, xdp_buff->data_hard_start + PAGE_SIZE, but
    ixgbe+virtio_net broke that assumption).

    It should actually be fairly easy to implement:
    * Simply extend xdp_buff with a "data_hard_end" pointer.

    Now cpumap is more safe... instead of crashing, it can now know/see when
    it is safe to create an SKB using build_skb (could fallback to
    dev_alloc_skb).

    --
    Best regards,
    Jesper Dangaard Brouer
    MSc.CS, Principal Kernel Engineer at Red Hat
    LinkedIn: http://www.linkedin.com/in/brouer

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