On Tue, Jun 26, 2018 at 8:19 PM Edward Cree <ec...@solarflare.com> wrote:
>
> __netif_receive_skb_taps() does a depressingly large amount of per-packet
> work that can't easily be listified, because the another_round looping
> makes it nontrivial to slice up into smaller functions.
> Fortunately, most of that work disappears in the fast path:
> * Hardware devices generally don't have an rx_handler
> * Unless you're tcpdumping or something, there is usually only one ptype
> * VLAN processing comes before the protocol ptype lookup, so doesn't force
> a pt_prev deliver
> so normally, __netif_receive_skb_taps() will run straight through and return
> the one ptype found in ptype_base[hash of skb->protocol].
>
> Signed-off-by: Edward Cree <ec...@solarflare.com>
> ---
> -static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc)
> +static int __netif_receive_skb_taps(struct sk_buff *skb, bool pfmemalloc,
> + struct packet_type **pt_prev)
A lot of code churn can be avoided by keeping local variable pt_prev and
calling this ppt_prev or so, then assigning just before returning on success.
Also, this function does more than just process network taps.
> {
> - struct packet_type *ptype, *pt_prev;
> rx_handler_func_t *rx_handler;
> struct net_device *orig_dev;
> bool deliver_exact = false;
> + struct packet_type *ptype;
> int ret = NET_RX_DROP;
> __be16 type;
>
> @@ -4514,7 +4515,7 @@ static int __netif_receive_skb_core(struct sk_buff
> *skb, bool pfmemalloc)
> skb_reset_transport_header(skb);
> skb_reset_mac_len(skb);
>
> - pt_prev = NULL;
> + *pt_prev = NULL;
>
> another_round:
> skb->skb_iif = skb->dev->ifindex;
> @@ -4535,25 +4536,25 @@ static int __netif_receive_skb_core(struct sk_buff
> *skb, bool pfmemalloc)
> goto skip_taps;
>
> list_for_each_entry_rcu(ptype, &ptype_all, list) {
> - if (pt_prev)
> - ret = deliver_skb(skb, pt_prev, orig_dev);
> - pt_prev = ptype;
> + if (*pt_prev)
> + ret = deliver_skb(skb, *pt_prev, orig_dev);
> + *pt_prev = ptype;
> }
