Hmmm, I wonder if 0 is the right thing vs something like 0xdeadc0de. We have a few explicit IVAR handlers that intentionally return a default value (e.g. acpi_get_handle()) and those do tend to be zero (and in those cases we don't KASSERT). I have a patch in a branch to add a new one like that for ThunderBolt PCI bridges even. 0 is probably fine as a default, but @imp might also have an opinion.

local and indentation

Make sense to me.

I've been traveling and haven't yet had time to review the latest changes, but last I looked it was moving in the right direction. Just give me a few more days.

Verified

phylosophically this interface more like L2 loopback, right?
can be emulated by ng_ether somehow?

• Make the netlink_writer cookie an honest const ifnet pointer.
• Refactor some code to provide the new constness constraint.

I think I'll try my luck with http://manuals.opensound.com/developer/mmap_test.c.html first and fit it into our example and once the usleep version works, see what are the values of ptr compared to the ones in kqueue scenario. My thinking is "if I can't fix it, move to simpler example", which I'm hoping the official docs are. Anyway, I didn't give up on this code, I just need to approach it from the different angle, for now.

No longer immediately relevant after the revert. Worth discussing the venn diagram regarding __ISO_C_VISIBLE et al since there are gotchas in C as well.