On Thu, 15 Mar 2018 16:13:39 +0100 Daniel Borkmann <dan...@iogearbox.net> wrote: > On 03/15/2018 01:50 PM, Shmulik Ladkani wrote: > > > > It would be beneficial to have the mark preserved when skb is injected > > to the slave device's rx path (especially when it's on the same netns). > > Right, I think also here the easiest would be to have a BPF_F_PRESERVE_MARK > flag to opt-in in general case (xnet/non-xnet)
Sounds okay to me. > But lets presume for a sec you would _not_ scrub it, then how are users > supposed to make use of this? The feature/bug may not be critical enough > (well, otherwise it wouldn't have been like this for long time) for stable, > so to write an app relying on it the behavior will change from kernel A to > kernel B, where you need to end up having a full blown veth run-time test > in order to figure it out before you can use it, not really useful either. Let's assume BPF_F_PRESERVE_MARK is a feature then, which is available only in new kernels. As said, this flag will not be honored by older kernels. But your "run-time test" argument is true for every new flag-bit introduced to bpf functions, for example: BPF_F_SEQ_NUMBER was added after other skb_set_tunnel_key flags, Same for BPF_F_INVALIDATE_HASH (skb_store_bytes), BPF_F_MARK_ENFORCE (l4_csum_replace) and others. With every flag addition, the flag mask validation in the corresponding bpf function has been relaxed to support it. Why is BPF_F_PRESERVE_MARK any different from any previous flag addition? Thanks, Shmulik
