On Sat, Sep 19, 2020 at 4:50 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > This series adds support attaching freplace BPF programs to multiple targets. > This is needed to support incremental attachment of multiple XDP programs using > the libxdp dispatcher model. > > The first patch fixes an issue that came up in review: The verifier will > currently allow MODIFY_RETURN tracing functions to attach to other BPF programs, > even though it is pretty clear from the commit messages introducing the > functionality that this was not the intention. This patch is included in the > serise because the subsequent refactoring patches touch the same code. > > The next three patches are refactoring patches: Patch 2 is a trivial change to > the logging in the verifier, split out to make the subsequent refactor easier to > read. Patch 3 refactors check_attach_btf_id() so that the checks on program and > target compatibility can be reused when attaching to a secondary location. > > Patch 4 moves prog_aux->linked_prog and the trampoline to be embedded in > bpf_tracing_link on attach, and freed by the link release logic, and introduces > a mutex to protect the writing of the pointers in prog->aux. > > Based on these refactorings, it becomes pretty straight-forward to support > multiple-attach for freplace programs (patch 5). This is simply a matter of > creating a second bpf_tracing_link if a target is supplied. However, for API > consistency with other types of link attach, this option is added to the > BPF_LINK_CREATE API instead of extending bpf_raw_tracepoint_open(). > > Patch 6 is a port of Jiri Olsa's patch to support fentry/fexit on freplace > programs. His approach of getting the target type from the target program > reference no longer works after we've gotten rid of linked_prog (because the > bpf_tracing_link reference disappears on attach). Instead, we used the saved > reference to the target prog type that is also used to verify compatibility on > secondary freplace attachment. > > Patches 7 is the accompanying libbpf update, and patches 8-10 are selftests: > patch 8 tests for the multi-freplace functionality itself, patch 9 is Jiri's > previous selftest for the fentry-to-freplace fix, and patch 10 is a test for > the change introduced in patch 1, blocking MODIFY_RETURN functions from > attaching to other BPF programs. > > With this series, libxdp and xdp-tools can successfully attach multiple programs > one at a time. To play with this, use the 'freplace-multi-attach' branch of > xdp-tools: > > $ git clone --recurse-submodules --branch freplace-multi-attach https://github.com/xdp-project/xdp-tools > $ cd xdp-tools/xdp-loader > $ make > $ sudo ./xdp-loader load veth0 ../lib/testing/xdp_drop.o > $ sudo ./xdp-loader load veth0 ../lib/testing/xdp_pass.o > $ sudo ./xdp-loader status > > The series is also available here: > https://git.kernel.org/pub/scm/linux/kernel/git/toke/linux.git/log/?h=bpf-freplace-multi-attach-alt-07 > > Changelog: > > v7: > - Add back missing ptype == prog->type check in link_create() > - Use tracing_bpf_link_attach() instead of separate freplace_bpf_link_attach() > - Don't break attachment of bpf_iters in libbpf What was specifically the issue and the fix for bpf_iters? [...]
