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So if the generated message would not fit > into the buffer, it's a caller bug. WARN_ON() is suitable for such > things, as it most probaly will hit the developer testing newly added > exack message. I disagree, extack is a best-effort diagnostic channel and it's valid for a caller to rely on e.g. %pI6c to generate messages that *usually* fit but can't be guaranteed to. And original dev might well not see the WARN_ON() because he's using addresses like fc00::123 in his tests whereas the end user — who maybe has panic_on_warn enabled — has a real-world address that takes 30+ bytes to print. Then there's things like %d which can vary in length by a factor of 10. I think the net_warn_ratelimited() with the full message, as I've used in v2, is plenty loud enough. -ed