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Merge branch 'bpf-verifier-log-rotation'
Andrii Nakryiko says: ==================== 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. Further, this patch set is merged with log_size_actual v1 patchset ([0]), which adds ability to get required log buffer size to fit entire verifier log output. This addresses a long-standing limitation, which causes users and BPF loader library writers to guess and pre-size log buffer, often allocating unnecessary extra memory for this or doing extra program verifications just to size logs better, ultimately wasting resources. This was requested most recently by Go BPF library maintainers ([1]). See respective patches for details. A bunch of them some drive-by fixes detecting during working with the code. Some other further refactor and compratmentalize verifier log handling code into kernel/bpf/log.c, which should also make it simpler to integrate such verbose log for other complicated bpf() syscall commands, if necessary. The rest are actual logic to calculate maximum log buffer size needed and return it to user-space. Few patches wire this on libbpf side, and the rest add selftests to test proper log truncation and log_buf==NULL handling. This turned into a pretty sizable patch set with lots of arithmetics, but hopefully the set of features added to verifier log in this patch set are both useful for BPF users and are self-contained and isolated enough to not cause troubles going forward. v3->v4: - s/log_size_actual/log_true_size/ (Alexei); - log_buf==NULL && log_size==0 don't trigger -ENOSPC (Lorenz); - added WARN_ON_ONCE if we try bpf_vlog_reset() forward (Lorenz); - added selftests for truncation in BPF_LOG_FIXED mode; - fixed edge case in BPF_LOG_FIXED when log_size==1, leaving buf not zero terminated; v2->v3: - typos and comment improvement (Lorenz); - merged with log_size_actual v1 ([0]) patch set (Alexei); - added log_buf==NULL condition allowed (Lorenz); - added BPF_BTF_LOAD logs tests (Lorenz); - more clean up and refactoring of internal verifier log API; v1->v2: - return -ENOSPC even in rotating log mode for preserving backwards compatibility (Lorenz); [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=735213&state=* [1] https://lore.kernel.org/bpf/CAN+4W8iNoEbQzQVbB_o1W0MWBDV4xCJAq7K3f6psVE-kkCfMqg@mail.gmail.com/ ==================== Signed-off-by: Daniel Borkmann <[email protected]>
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