Another option could be to use Serhiy’s proposed partial keywords support in Issue 26282. It is not yet committed, but it looks like it will go ahead, and then you could make “in” and “out” positional-only parameters, and the rest keywords. But IMO “src” and “dst” is fine.

Also, dropping “flags” support seems reasonable. One benefit is that if Linux added an unexpected flag in the future that conflicts with Python’s assumptions, it could do weird stuff or crash Python. See Issue 24933 for example, where socket.recv(n, MSG_TRUNC) returns uninitialized data.

The latest patch looks pretty good to me. Is there a consensus yet to add it as a public function? Before this goes in, it would be good to have a test case.