RE: [PATCH] net: support VLAN stacking packet type parsing

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Dengdui Huang [mailto:huangdengdui@huawei.com]
> Sent: Thursday, 3 July 2025 11.30
> 
> The current rte_net_get_ptype() only supports parsing packets with
> one 0x8100 VLAN tag or two 0x88a8 VLAN tags. This patch extends it
> to support parsing packets with two 0x8100 VLAN tags.
> 
> Signed-off-by: Dengdui Huang <huangdengdui@huawei.com>
> ---
>  lib/net/rte_net.c | 34 ++++++++++++++++++++++------------
>  lib/net/rte_net.h |  2 ++
>  2 files changed, 24 insertions(+), 12 deletions(-)
> 
> diff --git a/lib/net/rte_net.c b/lib/net/rte_net.c
> index 44fb6c0f51..fa8d023ca7 100644
> --- a/lib/net/rte_net.c
> +++ b/lib/net/rte_net.c
> @@ -352,14 +352,19 @@ uint32_t rte_net_get_ptype(const struct rte_mbuf
> *m,
>  	if (proto == rte_cpu_to_be_16(RTE_ETHER_TYPE_VLAN)) {
>  		const struct rte_vlan_hdr *vh;
>  		struct rte_vlan_hdr vh_copy;
> +		uint8_t vlan_num = 1;
> 
>  		pkt_type = RTE_PTYPE_L2_ETHER_VLAN;
> -		vh = rte_pktmbuf_read(m, off, sizeof(*vh), &vh_copy);
> -		if (unlikely(vh == NULL))
> -			return pkt_type;
> -		off += sizeof(*vh);
> -		hdr_lens->l2_len += sizeof(*vh);
> -		proto = vh->eth_proto;
> +		while (proto == rte_cpu_to_be_16(RTE_ETHER_TYPE_VLAN) &&
> +		       vlan_num <= MAX_VLAN_STACKING_TAGS) {
> +			vh = rte_pktmbuf_read(m, off, sizeof(*vh), &vh_copy);
> +			if (unlikely(vh == NULL))
> +				return pkt_type;
> +			off += sizeof(*vh);
> +			hdr_lens->l2_len += sizeof(*vh);
> +			proto = vh->eth_proto;
> +			vlan_num++;
> +		}

It's not that simple.

VLAN tags are not like MPLS labels.
With the MPLS packet type, we expect a stack of labels.
But with VLAN tagged packets, we expect exactly one VLAN tag at each outer/inner layer of headers. (Or no VLAN tag at the inner layer.)

This function already supports packets with 2 VLAN tags:
A stack of 2 VLAN tags is currently detected as 1 outer VLAN tag, adjusting hdr_lens->l2_len accordingly, and 1 inner VLAN tag, adjusting hdr_lens->inner_l2_len accordingly.
This behavior should not be changed.

I don't have a firm idea about how to better represent packets with a stack of 3+ VLAN tags than what we do today, so suggestions are welcome.

Which use case is this patch addressing?
Maybe information about the use case could guide us in some direction.

>  	} else if (proto == rte_cpu_to_be_16(RTE_ETHER_TYPE_QINQ)) {
>  		const struct rte_vlan_hdr *vh;
>  		struct rte_vlan_hdr vh_copy;
> @@ -504,15 +509,20 @@ uint32_t rte_net_get_ptype(const struct rte_mbuf
> *m,
>  	if (proto == rte_cpu_to_be_16(RTE_ETHER_TYPE_VLAN)) {
>  		const struct rte_vlan_hdr *vh;
>  		struct rte_vlan_hdr vh_copy;
> +		uint8_t vlan_num = 1;
> 
>  		pkt_type &= ~RTE_PTYPE_INNER_L2_MASK;
>  		pkt_type |= RTE_PTYPE_INNER_L2_ETHER_VLAN;
> -		vh = rte_pktmbuf_read(m, off, sizeof(*vh), &vh_copy);
> -		if (unlikely(vh == NULL))
> -			return pkt_type;
> -		off += sizeof(*vh);
> -		hdr_lens->inner_l2_len += sizeof(*vh);
> -		proto = vh->eth_proto;
> +		while (proto == rte_cpu_to_be_16(RTE_ETHER_TYPE_VLAN) &&
> +		       vlan_num <= MAX_VLAN_STACKING_TAGS) {
> +			vh = rte_pktmbuf_read(m, off, sizeof(*vh), &vh_copy);
> +			if (unlikely(vh == NULL))
> +				return pkt_type;
> +			off += sizeof(*vh);
> +			hdr_lens->inner_l2_len += sizeof(*vh);
> +			proto = vh->eth_proto;
> +			vlan_num++;
> +		}
>  	} else if (proto == rte_cpu_to_be_16(RTE_ETHER_TYPE_QINQ)) {
>  		const struct rte_vlan_hdr *vh;
>  		struct rte_vlan_hdr vh_copy;
> diff --git a/lib/net/rte_net.h b/lib/net/rte_net.h
> index 65d724b84b..fdd55d57c8 100644
> --- a/lib/net/rte_net.h
> +++ b/lib/net/rte_net.h
> @@ -13,6 +13,8 @@
>  extern "C" {
>  #endif
> 
> +#define MAX_VLAN_STACKING_TAGS	2
> +
>  /**
>   * Structure containing header lengths associated to a packet, filled
>   * by rte_net_get_ptype().
> --
> 2.33.0