Re: [PATCH dpdk v4] net/tap: use offsets provided by rte_net_get_ptype

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 12 May 2026 17:16:12 +0200
Robin Jarry <rjarry@redhat.com> wrote:

> Instead of guessing what are the proper header lengths, pass
> a rte_net_hdr_lens struct to rte_net_get_ptype and use it to get the
> proper header lengths/offsets in tap_verify_csum.
> 
> This allows supporting stacked VLAN/QinQ tags and IPv6 extensions.
> 
> Signed-off-by: Robin Jarry <rjarry@redhat.com>
> ---

AI patch review

Short summary suitable for replying to the patch:
The v4 patch claims to add IPv6 extension header support, but the L4
checksum path is broken for that case. The patch matches both IPV6
and IPV6_EXT in the L3 block and then falls through to
rte_ipv6_udptcp_cksum_verify(), which is documented as not supporting
extension headers. Concretely, that helper uses ipv6_hdr->proto for
the pseudo-header (which is the first extension-header type, not the
L4 protocol) and uses ipv6_hdr->payload_len as the raw-cksum length
(which over-reads past the L4 data by the size of the extensions).
Result: valid TCP/UDP over IPv6+ext packets get tagged
RX_L4_CKSUM_BAD, contradicting the commit message.
Suggested fix: keep IPV6_EXT in the L3 sanity-check block, but skip
L4 verification when l3 == RTE_PTYPE_L3_IPV6_EXT until a helper that
handles extension headers exists.