On Tue, 23 May 2023 11:10:38 +0300 Ido Schimmel wrote:

quoted

Can we possibly put the new field at the end of the CB and then have TC
look at it in the CB? We already do a bit of such CB juggling in strp
(first member of struct sk_skb_cb).  

Using the CB between different layers is very fragile and I would like
to avoid it. Note that the skb can pass various layers until hitting the
classifier, each of which can decide to memset() the CB.

Anyway, I think I have a better alternative. I added the 'l2_miss' bit
to the tc skb extension and adjusted the bridge to mark packets via this
extension. The entire thing is protected by the existing 'tc_skb_ext_tc'
static key, so overhead is kept to a minimum when feature is disabled.
Extended flower to enable / disable this key when filters that match on
'l2_miss' are added / removed.

bridge change to mark the packet:
https://github.com/idosch/linux/commit/3fab206492fcad9177f2340680f02ced1b9a0dec.patch

flow_dissector change to dissect the info from the extension:
https://github.com/idosch/linux/commit/1533c078b02586547817a4e63989a0db62aa5315.patch

flower change to enable / disable the key:
https://github.com/idosch/linux/commit/cf84b277511ec80fe565c41271abc6b2e2f629af.patch

Advantages compared to the previous approach are that we do not need a
new bit in the skb and that overhead is kept to a minimum when feature
is disabled. Disadvantage is that overhead is higher when feature is
enabled.

WDYT?

Sounds good, yup. Thanks!