On Sat, Jan 25, 2020 at 06:43:36PM -0700, David Ahern wrote:

That said, Martin's comment throws a wrench in the goal: if the existing
code does not enforce expected_attach_type then that option can not be
used in which case I guess I have to go with a new program type
(BPF_PROG_TYPE_XDP_EGRESS) which takes a new context (xdp_egress_md),
has different return codes, etc.

This is acceptable risk. We did such thing in the past. The chances of
user space breakage are extremely low.