veth: Add driver XDP
This is the basic implementation of veth driver XDP. Incoming packets are sent from the peer veth device in the form of skb, so this is generally doing the same thing as generic XDP. This itself is not so useful, but a starting point to implement other useful veth XDP features like TX and REDIRECT. This introduces NAPI when XDP is enabled, because XDP is now heavily relies on NAPI context. Use ptr_ring to emulate NIC ring. Tx function enqueues packets to the ring and peer NAPI handler drains the ring. Currently only one ring is allocated for each veth device, so it does not scale on multiqueue env. This can be resolved by allocating rings on the per-queue basis later. Note that NAPI is not used but netif_rx is used when XDP is not loaded, so this does not change the default behaviour. v6: - Check skb->len only when allocation is needed. - Add __GFP_NOWARN to alloc_page() as it can be triggered by external events. v3: - Fix race on closing the device. - Add extack messages in ndo_bpf. v2: - Squashed with the patch adding NAPI. - Implement adjust_tail. - Don't acquire consumer lock because it is guarded by NAPI. - Make poll_controller noop since it is unnecessary. - Register rxq_info on enabling XDP rather than on opening the device. Signed-off-by: NToshiaki Makita <makita.toshiaki@lab.ntt.co.jp> Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
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