On 4 Jun 2019, at 9:43, Jesper Dangaard Brouer wrote: > On Mon, 3 Jun 2019 09:38:51 -0700 > Jonathan Lemon <jonathan.le...@gmail.com> wrote: > >> Currently, the AF_XDP code uses a separate map in order to >> determine if an xsk is bound to a queue. Instead of doing this, >> have bpf_map_lookup_elem() return the queue_id, as a way of >> indicating that there is a valid entry at the map index. > > Just a reminder, that once we choose a return value, there the > queue_id, then it basically becomes UAPI, and we cannot change it.
Yes - Alexei initially wanted to return the sk_cookie instead, but that's 64 bits and opens up a whole other can of worms. > Can we somehow use BTF to allow us to extend this later? > > I was also going to point out that, you cannot return a direct pointer > to queue_id, as BPF-prog side can modify this... but Daniel already > pointed this out. So, I see three solutions here (for this and Toke's patchset also, which is encountering the same problem). 1) add a scratch register (Toke's approach) 2) add a PTR_TO_<type>, which has the access checked. This is the most flexible approach, but does seem a bit overkill at the moment. 3) add another helper function, say, bpf_map_elem_present() which just returns a boolean value indicating whether there is a valid map entry or not. I was starting to do 2), but wanted to get some more feedback first. -- Jonathan
