Hi Toke, On Thu, Aug 18, 2022 at 09:52:08PM +0200, Toke Høiland-Jørgensen wrote: > Daniel Xu <dxu@xxxxxxxxx> writes: > > > Support direct writes to nf_conn:mark from TC and XDP prog types. This > > is useful when applications want to store per-connection metadata. This > > is also particularly useful for applications that run both bpf and > > iptables/nftables because the latter can trivially access this > > metadata. > > Looking closer at the nf_conn definition, the mark field (and possibly > secmark) seems to be the only field that is likely to be feasible to > support direct writes to, as everything else either requires special > handling (like status and timeout), or they are composite field that > will require helpers anyway to use correctly. > > Which means we're in the process of creating an API where users have to > call helpers to fill in all fields *except* this one field that happens > to be directly writable. That seems like a really confusing and > inconsistent API, so IMO it strengthens the case for just making a > helper for this field as well, even though it adds a bit of overhead > (and then solving the overhead issue in a more generic way such as by > supporting clever inlining). > > -Toke I don't particularly have a strong opinion here. But to play devil's advocate: * It may be confusing now, but over time I expect to see more direct write support via BTF, especially b/c there is support for unstable helpers now. So perhaps in the future it will seem more sensible. * The unstable helpers do not have external documentation. Nor should they in my opinion as their unstableness + stale docs may lead to undesirable outcomes. So users of the unstable API already have to splunk through kernel code and/or selftests to figure out how to wield the APIs. All this to say there may not be an argument for discoverability. * Direct writes are slightly more ergnomic than using a helper. Thanks, Daniel
