[PATCH v3 0/9] virtio-net: support multi buffer xdp

[Heng Qi <hengqi@linux.alibaba.com>]

Changes since PATCH v2:
- Even if single buffer xdp has a hole mechanism, there will be no
  problem (limiting mtu and turning off GUEST GSO), so there is no
  need to backport "[PATCH 1/9]";
- Modify calculation of MTU for single buffer xdp in virtnet_xdp_set();
- Make truesize in mergeable mode return to literal meaning;
- Add some comments for legibility;

Changes since RFC:
- Using headroom instead of vi->xdp_enabled to avoid re-reading
  in add_recvbuf_mergeable();
- Disable GRO_HW and keep linearization for single buffer xdp;
- Renamed to virtnet_build_xdp_buff_mrg();
- pr_debug() to netdev_dbg();
- Adjusted the order of the patch series.

Currently, virtio net only supports xdp for single-buffer packets
or linearized multi-buffer packets. This patchset supports xdp for
multi-buffer packets, then larger MTU can be used if xdp sets the
xdp.frags. This does not affect single buffer handling.

In order to build multi-buffer xdp neatly, we integrated the code
into virtnet_build_xdp_buff_mrg() for xdp. The first buffer is used
for prepared xdp buff, and the rest of the buffers are added to
its skb_shared_info structure. This structure can also be
conveniently converted during XDP_PASS to get the corresponding skb.

Since virtio net uses comp pages, and bpf_xdp_frags_increase_tail()
is based on the assumption of the page pool,
(rxq->frag_size - skb_frag_size(frag) - skb_frag_off(frag))
is negative in most cases. So we didn't set xdp_rxq->frag_size in
virtnet_open() to disable the tail increase.

Heng Qi (9):
  virtio-net: disable the hole mechanism for xdp
  virtio-net: set up xdp for multi buffer packets
  virtio-net: update bytes calculation for xdp_frame
  virtio-net: build xdp_buff with multi buffers
  virtio-net: construct multi-buffer xdp in mergeable
  virtio-net: transmit the multi-buffer xdp
  virtio-net: build skb from multi-buffer xdp
  virtio-net: remove xdp related info from page_to_skb()
  virtio-net: support multi-buffer xdp

 drivers/net/virtio_net.c | 371 ++++++++++++++++++++++++++-------------
 1 file changed, 250 insertions(+), 121 deletions(-)

-- 
2.19.1.6.gb485710b