[PATCH bpf-next v4 0/4] bpf: Improve error reporting for freplace attachment failure

Leon Hwang
2025-02-24T15:34:39Z

This patch series improves error reporting for BPF_LINK_CREATE when
attaching freplace programs. Inspired by the discussion in
"[PATCH bpf-next v2] bpf: Add bpf_check_attach_target_with_klog method to
output failure logs to kernel"[0], this series enhances that freplace
attachment failure returns meaningful logs to userspace, aiding debugging.

Patch breakdown:
1. bpf, verifier: Add missing newline of bpf_log in bpf_check_attach_target
* Add the missing newline in
bpf_log(log, "Target program bound device mismatch").
2. bpf: Improve error reporting for freplace attachment failure
* Extends BPF_LINK_CREATE to report detailed log.
3. bpf, libbpf: Capture error message of freplace attachment failure
* Modifies libbpf to capture freplace attachment failure log.
4. selftests/bpf: Add test case for freplace attachment failure log
* Introduces a selftest to validate error reporting.

Links:
[0] https://lore.kernel.org/bpf/CAEf4BzbbyojuFSS7xQ3+jZb=dHzOaZfMbtT+WnypW2LPwOUwRw@mail.gmail.com/

Changes:
v3 -> v4:
* Add libbpf API bpf_program__attach_freplace_opts() to use users'
supplied log buffer.

v2: https://lore.kernel.org/bpf/20240725051511.57112-1-me@manjusaka.me/
v2 -> v3:
* Address comment from Andrii:
* Report back the reason for declining freplace attachment instead of
logging in dmesg.

Leon Hwang (4):
bpf, verifier: Add missing newline of bpf_log in
bpf_check_attach_target
bpf: Improve error reporting for freplace attachment failure
bpf, libbpf: Capture error message of freplace attachment failure
selftests/bpf: Add test case for freplace attachment failure log

include/uapi/linux/bpf.h | 2 +
kernel/bpf/syscall.c | 51 ++++++++++++++++---
kernel/bpf/verifier.c | 2 +-
tools/include/uapi/linux/bpf.h | 2 +
tools/lib/bpf/bpf.c | 6 ++-
tools/lib/bpf/bpf.h | 2 +
tools/lib/bpf/libbpf.c | 29 +++++++++--
tools/lib/bpf/libbpf.h | 14 +++++
tools/lib/bpf/libbpf.map | 1 +
.../bpf/prog_tests/tracing_link_attach_log.c | 48 +++++++++++++++++
10 files changed, 143 insertions(+), 14 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/tracing_link_attach_log.c

--
2.47.1