On 2019-06-04 19:25, 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.
Hmm, what other info would be useful? ifindex? Or going the the
other way, with read-only and just returning boolean?
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.
Ugh, good thing Daniel found this!
Björn
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.
