On Tue, Oct 3, 2017 at 12:46 AM, Jiri Pirko <j...@resnulli.us> wrote: > Fri, Sep 29, 2017 at 07:59:35PM CEST, t...@herbertland.com wrote: >>On Fri, Sep 29, 2017 at 10:42 AM, David Miller <da...@davemloft.net> wrote: >>> From: Tom Herbert <t...@herbertland.com> >>> Date: Fri, 29 Sep 2017 08:48:55 -0700 >>> >>>> The flow_dissector interface is not a uAPI. >>> >>> That's not true, insofar as cls_flower.c uses the flow_dissector >>> therefore if you change the flow_dissector in certain ways then >>> cls_flower.c might have it's behavior changed and that is in fact UAPI >>> facing. >> >>Then I would suggest adding another flag like FLOW_DISSECTOR_F_FLOWER >>and when anyone puts new code into flow_dissector they can wrap it >>with "if !(flags & FLOW_DISSECTOR_F_FLOWER)". If the flower uAPI is >>subsequently update then the conditional can be removed. This way >>flower can support maintain its APIs, but we can still still extend >>and improve flow_dissector for othersuse cases. > > This is not flower-specific problem. Flow_dissector is a servant of many.
Besides flower, what other use cases of flow_dissector have made flow_dissector interface a uAPI? Any use of hashing does not do this. Maybe OVS does? > As such, it is instructed what should it do. If you want to > change the way inner headers are parsed, you should either: Why would that only affect the way inner headers are parsed? Wouldn't we need to consider any change to flow_dissector that might affect the output in any way. For instance, the depth limits I added would change to output for someone that was parsing thirty-five layers of encapsulation so it it looks like that feature needs a flag. What if someone adds a new Ethernet protocol or a new encap protocol? > 1) change the callers so they are behaving the same as before > 2) make the flow_dissection change optional so the caller can say if he > wants original or new behaviour. I guess we can do that, but am concerned about the overhead this will generate if were adding a flag each time anyone modifies the function. There are performance critical use cases of flow_dissector that will be impacted by such changes. Tom >
