This patch set changes BPF verifier log behavior to behave as a rotating log, by default. If user-supplied log buffer is big enough to contain entire verifier log output, there is no effective difference. But where previously user supplied too small log buffer and would get -ENOSPC error result and the beginning part of the verifier log, now there will be no error and user will get ending part of verifier log filling up user-supplied log buffer. Which is, in absolute majority of cases, is exactly what's useful, relevant, and what users want and need, as the ending of the verifier log is containing details of verifier failure and relevant state that got us to that failure. So this rotating mode is made default, but for some niche advanced debugging scenarios it's possible to request old behavior by specifying additional BPF_LOG_FIXED (8) flag. This patch set adjusts libbpf to allow specifying flags beyond 1 | 2 | 4. We also add --log-size and --log-fixed options to veristat to be able to both test this functionality manually, but also to be used in various debugging scenarios. We also add selftests that tries many variants of log buffer size to stress-test correctness of internal verifier log bookkeeping code. Andrii Nakryiko (6): bpf: split off basic BPF verifier log into separate file bpf: remove minimum size restrictions on verifier log buffer bpf: switch BPF verifier log to be a rotating log by default libbpf: don't enfore verifier log levels on libbpf side selftests/bpf: add more veristat control over verifier log options selftests/bpf: add fixed vs rotating verifier log tests include/linux/bpf_verifier.h | 47 ++-- kernel/bpf/Makefile | 3 +- kernel/bpf/log.c | 251 ++++++++++++++++++ kernel/bpf/verifier.c | 86 +----- tools/lib/bpf/bpf.c | 2 - .../selftests/bpf/prog_tests/log_fixup.c | 1 + .../selftests/bpf/prog_tests/verifier_log.c | 89 +++++++ tools/testing/selftests/bpf/veristat.c | 42 ++- 8 files changed, 416 insertions(+), 105 deletions(-) create mode 100644 kernel/bpf/log.c create mode 100644 tools/testing/selftests/bpf/prog_tests/verifier_log.c -- 2.34.1
