Re: [PATCH v2 net-next 4/4] net: dsa: tag_dsa: Support reception of packets from LAG devices

Tobias Waldekranz
2020-12-01T22:32:03Z

On Tue, Dec 01, 2020 at 23:24, Vladimir Oltean <olteanv@gmail.com> wrote:
> On Mon, Nov 30, 2020 at 03:06:10PM +0100, Tobias Waldekranz wrote:
>> Packets ingressing on a LAG that egress on the CPU port, which are not
>> classified as management, will have a FORWARD tag that does not
>> contain the normal source device/port tuple. Instead the trunk bit
>> will be set, and the port field holds the LAG id.
>>
>> Since the exact source port information is not available in the tag,
>> frames are injected directly on the LAG interface and thus do never
>> pass through any DSA port interface on ingress.
>>
>> Management frames (TO_CPU) are not affected and will pass through the
>> DSA port interface as usual.
>>
>> Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
>> ---
>> net/dsa/dsa.c | 12 +++++++++++-
>> net/dsa/tag_dsa.c | 17 ++++++++++++++++-
>> 2 files changed, 27 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
>> index a1b1dc8a4d87..7325bf4608e9 100644
>> --- a/net/dsa/dsa.c
>> +++ b/net/dsa/dsa.c
>> @@ -219,11 +219,21 @@ static int dsa_switch_rcv(struct sk_buff *skb, struct net_device *dev,
>> }
>>
>> skb = nskb;
>> - p = netdev_priv(skb->dev);
>> skb_push(skb, ETH_HLEN);
>> skb->pkt_type = PACKET_HOST;
>> skb->protocol = eth_type_trans(skb, skb->dev);
>>
>> + if (unlikely(!dsa_slave_dev_check(skb->dev))) {
>> + /* Packet is to be injected directly on an upper
>> + * device, e.g. a team/bond, so skip all DSA-port
>> + * specific actions.
>> + */
>> + netif_rx(skb);
>> + return 0;
>
> netif_rx returns an int code, it seems odd to ignore it.

This is exactly the same treatment that the return code from
gro_cells_receive gets just a few lines down. They return the same set
of codes (NET_RX_{SUCCESS,DROP}).

Looking through the source base, there are a few callers that look at
the return value (the overwhelming majority ignore it). Actions vary
from printing warnings (without rate-limit, yikes), setting variables
that are otherwise unused, or bumping a counter (the only reasonable
thing I have seen).

But looking through enqueue_to_backlog, it seems like there already is a
counter for this that is accessible from /proc/net/softnet_data.

>> + }
>> +
>> + p = netdev_priv(skb->dev);
>> +
>> if (unlikely(cpu_dp->ds->untag_bridge_pvid)) {
>> nskb = dsa_untag_bridge_pvid(skb);
>> if (!nskb) {