netdev - Conntrack offload and ingress

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Date:   Fri, 1 Apr 2022 11:40:52 +0100
From:   Edward Cree <ecree.xilinx@...il.com>
To:     pablo@...filter.org
Cc:     Network Development <netdev@...r.kernel.org>,
        netfilter-devel@...r.kernel.org
Subject: Conntrack offload and ingress_ifindex

Pablo,

When developing a conntrack offload driver, I was quite surprised to find
 that CT entries passed to the driver's flow-block callback (as registered
 with nf_flow_table_offload_add_cb()) include a match on ingress_ifindex,
 with mask 0xffffffff and key 0.  This is especially confusing as AIUI 0 is
 not a valid ifindex.
>From reading the calling code, looking at git logs etc, I can't determine
 the intended semantics of this match; could you clarify what (if anything)
 drivers are expected to do with it?
(Looking at other drivers it appears that e.g. mlx5e simply ignores it, as
 its test for `key & mask` in mlx5_tc_ct_set_tuple_match() will be false.)

-ed