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

[Leon Hwang <leon.hwang@linux.dev>]

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