On Tue, Mar 28, 2023 at 4:59 PM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Tue, Mar 28, 2023 at 4:56 PM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote: > > > > 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. > > > > v1->v2: > > - return -ENOSPC even in rotating log mode for preserving backwards > > compatibility (Lorenz); > > I haven't implemented the feature we discussed, where the > BPF_PROG_LOAD (and BPF_BTF_LOAD) command will return back the full > size of the buffer that's necessary to contain the complete log > buffer. I'm building it on top of this patch set and would like to > send it separately as a follow up, as it touches UAPI some more, and I > feel like we'll have few revisions just for this. So I didn't want to > delay these changes. Plus, I think to add this even for BPF_LOG_FIXED > mode, so it's provided consistently. So I need a bit more time to > implement this. Hopefully this version will work for everyone and can > go in sooner. Lorenz, ping.
