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.
For example, when attempting to attach a freplace program to a static
function:
libbpf: prog 'new_test_pkt_access': failed to attach to freplace: -EINVAL
libbpf: prog 'new_test_pkt_access': attach log: subprog_tail() is not a global function
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: Report log of freplace attach failure
* Extends BPF_LINK_CREATE to report detailed error logs.
3. bpf, libbpf: Capture log of freplace attach failure
* Modifies libbpf to capture and print attachment logs.
4. selftests/bpf: Add a test case for freplace attachment failure logging
* Introduces a selftest to validate error reporting.
Links:
[0] https://lore.kernel.org/bpf/CAEf4BzbbyojuFSS7xQ3+jZb=dHzOaZfMbtT+WnypW2LPwOUwRw@xxxxxxxxxxxxxx/
Changes:
v2: https://lore.kernel.org/bpf/20240725051511.57112-1-me@xxxxxxxxxxxx/
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 and log freplace attachment failure
selftests/bpf: Add test case for freplace attachment failure logging
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 | 14 ++++-
.../bpf/prog_tests/tracing_link_attach_log.c | 42 +++++++++++++++
8 files changed, 109 insertions(+), 12 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/tracing_link_attach_log.c
--
2.47.1
