On Tue, 4 Jun 2019 at 20:13, Martin Lau <ka...@fb.com> wrote: > > On Tue, Jun 04, 2019 at 10:25:23AM -0700, Jonathan Lemon wrote: > > 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. > I think it would be nice and more extensible to have PTR_TO_xxx. > It could start with the existing PTR_TO_SOCKET > > or starting with a new PTR_TO_XDP_SOCK from the beginning is also fine. >
Doesn't the PTR_TO_SOCKET path involve taking a ref and mandating sk_release() from the fast path? :-( Björn > > 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
