netdev - TC stats / hw offload question

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Date:   Tue, 5 Feb 2019 19:41:12 +0000
From:   Edward Cree <ecree@...arflare.com>
To:     netdev <netdev@...r.kernel.org>
CC:     Jiri Pirko <jiri@...nulli.us>, Jamal Hadi Salim <jhs@...atatu.com>,
        "Cong Wang" <xiyou.wangcong@...il.com>
Subject: TC stats / hw offload question

Regarding TC_CLSFLOWER_STATS, when a filter rule modifies the length of
 the packet, e.g. by adding a VLAN or encap header, should the bytes
 counter count the length of the packet _before_ edits (i.e. as seen by
 the match), or the length after edits?  If the latter, what is the
 correct behaviour when (say) a packet is mirrored as-is but also
 redirected with encapsulation?
The fact that the stats live in the struct tc_action suggests a per-
 action connection that would imply post-edit length, but then in
 tcf_exts_dump_stats() we only look at the first action, which seems to
 imply we really want the pre-edit length.
I can't find any kind of doc or spec defining what behaviour is required.

-Ed