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Date:   Mon, 23 Jul 2018 17:23:24 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Toshiaki Makita <toshiaki.makita1@...il.com>
Cc:     netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH v3 bpf-next 2/8] veth: Add driver XDP

On Mon, 23 Jul 2018 00:13:02 +0900, Toshiaki Makita wrote:
> From: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> 
> 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.
> 
> 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: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>

> +static struct sk_buff *veth_xdp_rcv_skb(struct veth_priv *priv,
> +					struct sk_buff *skb)
> +{
> +	u32 pktlen, headroom, act, metalen;
> +	void *orig_data, *orig_data_end;
> +	int size, mac_len, delta, off;
> +	struct bpf_prog *xdp_prog;
> +	struct xdp_buff xdp;
> +
> +	rcu_read_lock();
> +	xdp_prog = rcu_dereference(priv->xdp_prog);
> +	if (unlikely(!xdp_prog)) {
> +		rcu_read_unlock();
> +		goto out;
> +	}
> +
> +	mac_len = skb->data - skb_mac_header(skb);
> +	pktlen = skb->len + mac_len;
> +	size = SKB_DATA_ALIGN(VETH_XDP_HEADROOM + pktlen) +
> +	       SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> +	if (size > PAGE_SIZE)
> +		goto drop;
> +
> +	headroom = skb_headroom(skb) - mac_len;
> +	if (skb_shared(skb) || skb_head_is_locked(skb) ||
> +	    skb_is_nonlinear(skb) || headroom < XDP_PACKET_HEADROOM) {
> +		struct sk_buff *nskb;
> +		void *head, *start;
> +		struct page *page;
> +		int head_off;
> +
> +		page = alloc_page(GFP_ATOMIC);
> +		if (!page)
> +			goto drop;
> +
> +		head = page_address(page);
> +		start = head + VETH_XDP_HEADROOM;
> +		if (skb_copy_bits(skb, -mac_len, start, pktlen)) {
> +			page_frag_free(head);
> +			goto drop;
> +		}
> +
> +		nskb = veth_build_skb(head,
> +				      VETH_XDP_HEADROOM + mac_len, skb->len,
> +				      PAGE_SIZE);
> +		if (!nskb) {
> +			page_frag_free(head);
> +			goto drop;
> +		}

> +static int veth_enable_xdp(struct net_device *dev)
> +{
> +	struct veth_priv *priv = netdev_priv(dev);
> +	int err;
> +
> +	if (!xdp_rxq_info_is_reg(&priv->xdp_rxq)) {
> +		err = xdp_rxq_info_reg(&priv->xdp_rxq, dev, 0);
> +		if (err < 0)
> +			return err;
> +
> +		err = xdp_rxq_info_reg_mem_model(&priv->xdp_rxq,
> +						 MEM_TYPE_PAGE_SHARED, NULL);

nit: doesn't matter much but looks like a mix of MEM_TYPE_PAGE_SHARED
     and MEM_TYPE_PAGE_ORDER0

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