On Mon, Jul 10, 2023 at 06:51:19PM +0200, Ilya Maximets wrote: > On 7/8/23 00:06, Jakub Kicinski wrote: > > On Fri, 7 Jul 2023 18:04:36 +0200 Ilya Maximets wrote: > >>>> That already exists, right? Johannes added it in the last release for > >>>> WiFi. > >>> > >>> I'm not sure. The SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE behaves > >>> similarly > >>> to that on a surface. However, looking closer, any value that can be > >>> passed > >>> into ieee80211_rx_handlers_result() and ends up in the kfree_skb_reason() > >>> is > >>> kind of defined in net/mac80211/drop.h, unless I'm missing something (very > >>> possible, because I don't really know wifi code). > >>> > >>> The difference, I guess, is that for openvswitch values will be provided > >>> by > >>> the userpsace application via netlink interface. It'll be just a number > >>> not > >>> defined anywhere in the kernel. Only the subsystem itself will be defined > >>> in order to occupy the range. Garbage in, same garbage out, from the > >>> kernel's > >>> perspective. > >> > >> To be clear, I think, not defining them in this particular case is better. > >> Definition of every reason that userspace can come up with will add extra > >> uAPI maintenance cost/issues with no practical benefits. Values are not > >> going to be used for anything outside reporting a drop reason and subsystem > >> offset is not part of uAPI anyway. > > > > Ah, I see. No, please don't stuff user space defined values into > > the drop reason. The reasons are for debugging the kernel stack > > itself. IOW it'd be abuse not reuse. > > Makes sense. I wasn't sure that's a good solution from a kernel perspective > either. It's better than defining all these reasons, IMO, but it's not good > enough to be considered acceptable, I agree. > > How about we define just 2 reasons, e.g. OVS_DROP_REASON_EXPLICIT_ACTION and > OVS_DROP_REASON_EXPLICIT_ACTION_WITH_ERROR (exact names can be different) ? > One for an explicit drop action with a zero argument and one for an explicit > drop with non-zero argument. > > The exact reason for the error can be retrieved by other means, i.e by looking > at the datapath flow dump or OVS logs/traces. > > This way we can give a user who is catching packet drop traces a signal that > there was something wrong with an OVS flow and they can look up exact details > from the userspace / flow dump. > > The point being, most of the flows will have a zero as a drop action argument, > i.e. a regular explicit packet drop. It will be hard to figure out which flow > exactly we're hitting without looking at the full flow dump. And if the value > is non-zero, then it should be immediately obvious which flow is to blame from > the dump, as we should not have a lot of such flows. > > This would still allow us to avoid a maintenance burden of defining every > case, > which are fairly meaningless for the kernel itself, while having 99% of the > information we may need. > > Jakub, do you think this will be acceptable? > > Eric, Adrian, Aaron, do you see any problems with such implementation?
I see no problems. I'm content with this approach. > P.S. There is a plan to add more drop reasons for other places in openvswitch > module to catch more regular types of drops like memory issues or upcall > failures. So, the drop reason subsystem can be extended later. > The explicit drop action is a bit of an odd case here. > > Best regards, Ilya Maximets. > _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
