David Ahern <dsah...@gmail.com> writes: > On 5/18/20 3:08 AM, Toke Høiland-Jørgensen wrote: >> I can see your point that fixing up the whole skb after the program has >> run is not a good idea. But to me that just indicates that the hook is >> in the wrong place: that it really should be in the driver, executed at >> a point where the skb data structure is no longer necessary (similar to >> how the ingress hook is before the skb is generated). > > Have you created a cls_bpf program to modify skbs? Have you looked at > the helpers, the restrictions and the tight management of skb changes? > Have you followed the skb from create to device handoff through the > drivers? Have you looked at the history of encapsulations, gso handling, > offloads, ...?
Have you tried re-reading the first sentence of the paragraph you're replying to? You know, the one that started with "I can see your point that..." >> Otherwise, what you're proposing is not an egress hook, but rather a >> 'post-REDIRECT hook', which is strictly less powerful. This may or may >> not be useful in its own right, but let's not pretend it's a full egress >> hook. Personally I feel that the egress hook is what we should be going >> for, not this partial thing. > > You are hand waving. Be specific, with details. Are you deliberately trying to antagonise me or something? It's a really odd way to try to make your case... > Less powerful how? There are only so many operations you can do to a > packet. What do you want to do and what can't be done with this proposed > change? Why must it be done as XDP vs proper synergy between the 2 paths. I meant 'less powerful' in the obvious sense: it only sees a subset of the packets going out of the interface. And so I worry that it will (a) make an already hard to use set of APIs even more confusing, and (b) turn out to not be enough so we'll end up needing a "real" egress hook. As I said in my previous email, a post-REDIRECT hook may or may not be useful in its own right. I'm kinda on the fence about that, but am actually leaning towards it being useful; however, I am concerned that it'll end up being redundant if we do get a full egress hook. -Toke
