Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > On Fri, Sep 11, 2020 at 3:01 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: >> >> From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> >> >> This enables support for attaching freplace programs to multiple attach >> points. It does this by amending UAPI for bpf_raw_tracepoint_open with a >> target prog fd and btf ID pair that can be used to supply the new >> attachment point. The target must be compatible with the target that was >> supplied at program load time. >> >> The implementation reuses the checks that were factored out of >> check_attach_btf_id() to ensure compatibility between the BTF types of the >> old and new attachment. If these match, a new bpf_tracing_link will be >> created for the new attach target, allowing multiple attachments to >> co-exist simultaneously. >> >> The code could theoretically support multiple-attach of other types of >> tracing programs as well, but since I don't have a use case for any of >> those, the bpf_tracing_prog_attach() function will reject new targets for >> anything other than PROG_TYPE_EXT programs. >> >> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> >> --- > > It feels like using a semi-constructed bpf_tracing_link inside > prog->aux->tgt_link is just an unnecessary complication, after reading > this and previous patches. Seems more straightforward and simpler to > store tgt_attach_type/tgt_prog_type (permanently) and > tgt_prog/tgt_trampoline (until first attachment) in prog->aux and then > properly create bpf_link on attach. I updated v4 with your comments, but kept the link in prog->aux; the reason being that having a container for the two pointers makes it possible to atomically swap it out with xchg() as you suggested previously. Could you please take a look at v4? If you still think it's better to just keep two separate pointers (and add a lock) in prog->aux, I can change it to that. But I'd rather avoid the lock if possible... -Toke
