Re: [PATCH bpf-next 1/3] bpf: Introduce dynamic program extensions

On 1/20/20 2:52 PM, Andrii Nakryiko wrote:

quoted

+       }
+       if (tr->extension_prog) {
+               /* cannot attach fentry/fexit if extension prog is attached */
+               err = -EBUSY;
+               goto out;
+       }

move this check before BPF_TRAMP_REPLACE check and check additonally
for fentry+fexit for BPF_TRAMP_REPLACE? Nothing can replace
extension_prog, right?

makes sense. fixed.

quoted

+               if (tgt_prog->type == BPF_PROG_TYPE_TRACING &&
+                   tgt_prog->expected_attach_type != BPF_TRACE_RAW_TP &&

if the intent is to prevent extending FENTRY/FEXIT, why not checking
explicitly for those two instead of making assumption that
expected_attach_type can be only one of RAW_TP/FENTRY/FEXIT, this can
easily change in the future. Besides, direct FENTRY/FEXIT comparison
is more self-documenting as well.

sure. fixed as well.

quoted

                 }
+               if (prog_extension &&
+                   btf_check_type_match(env, prog, btf, t))

this reads so weird... btf_check_type_match (and
btf_check_func_type_match as well) are boolean functions (i.e., either
matches or not, or some error), why not using a conventional
boolean+error return convention: 0 - false, 1 - true, <0 - error
(bug)?

I cannot agree here. Such return convention will be very odd.
The one I picked is consistent with other places.