On 18/05/2023 14:33, Ido Schimmel wrote:
> Allow the bridge driver to mark packets that did not match a layer 2
> entry during forwarding by adding a 'l2_miss' bit to the skb.
>
> Clear the bit whenever a packet enters the bridge (received from a
> bridge port or transmitted via the bridge) and set it if the packet did
> not match an FDB/MDB entry.
>
> Subsequent patches will allow the flower classifier to match on this
> bit. The motivating use case in non-DF (Designated Forwarder) filtering
> where we would like to prevent decapsulated packets from being flooded
> to a multi-homed host.
>
> Do not allocate the bit if the kernel was not compiled with bridge
> support and place it after the two bit fields in accordance with commit
> 4c60d04c2888 ("net: skbuff: push nf_trace down the bitfield"). The bit
> does not increase the size of the structure as it is placed at an
> existing hole. Layout with allmodconfig:
>
> struct sk_buff {
> [...]
> __u8 csum_not_inet:1; /* 132: 3 1 */
> __u8 l2_miss:1; /* 132: 4 1 */
>
> /* XXX 3 bits hole, try to pack */
> /* XXX 1 byte hole, try to pack */
>
> __u16 tc_index; /* 134 2 */
> u16 alloc_cpu; /* 136 2 */
> [...]
> } __attribute__((__aligned__(8)));
>
> Signed-off-by: Ido Schimmel <idosch@xxxxxxxxxx>
> ---
> include/linux/skbuff.h | 4 ++++
> net/bridge/br_device.c | 1 +
> net/bridge/br_forward.c | 3 +++
> net/bridge/br_input.c | 1 +
> 4 files changed, 9 insertions(+)
>
[snip]
> while (p || rp) {
> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> index fc17b9fd93e6..d8ab5890cbe6 100644
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> @@ -334,6 +334,7 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
> return RX_HANDLER_CONSUMED;
>
> memset(skb->cb, 0, sizeof(struct br_input_skb_cb));
> + skb->l2_miss = 0;
>
> p = br_port_get_rcu(skb->dev);
> if (p->flags & BR_VLAN_TUNNEL)
Overall looks good, only this part is a bit worrisome and needs some additional
investigation because now we'll unconditionally dirty a cache line for every
packet that is forwarded. Could you please check the effect with perf?
Thanks,
Nik
