The state of bpf(2) manual pages today is not exactly ideal. For the most part, it was written several years ago and has not kept up with the pace of development in the kernel tree. For instance, out of a total of ~35 commands to the BPF syscall available today, when I pull the kernel-man-pages tree today I find just 6 documented commands: The very basics of map interaction and program load. In contrast, looking at bpf-helpers(7), I am able today to run one command[0] to fetch API documentation of the very latest eBPF helpers that have been added to the kernel. This documentation is up to date because kernel maintainers enforce documenting the APIs as part of the feature submission process. As far as I can tell, we rely on manual synchronization from the kernel tree to the kernel-man-pages tree to distribute these more widely, so all locations may not be completely up to date. That said, the documentation does in fact exist in the first place which is a major initial hurdle to overcome. Given the relative success of the process around bpf-helpers(7) to encourage developers to document their user-facing changes, in this patch series I explore applying this technique to bpf(2) as well. Unfortunately, even with bpf(2) being so out-of-date, there is still a lot of content to convert over. In particular, the following aspects of the bpf syscall could also be individually be generated from separate documentation in the header: * BPF syscall commands * BPF map types * BPF program types * BPF program subtypes (aka expected_attach_type) * BPF attachment points Rather than tackle everything at once, I have focused in this series on the syscall commands, "enum bpf_cmd". This series is structured to first import what useful descriptions there are from the kernel-man-pages tree, then piece-by-piece document a few of the syscalls in more detail in cases where I could find useful documentation from the git tree or from a casual read of the code. Not all documentation is comprehensive at this point, but a basis is provided with examples that can be further enhanced with subsequent follow-up patches. Note, the series in its current state only includes documentation around the syscall commands themselves, so in the short term it doesn't allow us to automate bpf(2) generation; Only one section of the man page could be replaced. Though if there is appetite for this approach, this should be trivial to improve on, even if just by importing the remaining static text from the kernel-man-pages tree. Following that, the series enhances the python scripting around parsing the descriptions from the header files and generating dedicated ReStructured Text and troff output. Finally, to expose the new text and reduce the likelihood of having it get out of date or break the docs parser, it is added to the selftests and exposed through the kernel documentation web pages. The eventual goal of this effort would be to extend the kernel UAPI headers such that each of the categories I had listed above (commands, maps, progs, hooks) have dedicated documentation in the kernel tree, and that developers must update the comments in the headers to document the APIs prior to patch acceptance, and that we could auto-generate the latest version of the bpf(2) manual pages based on a few static description sections combined with the dynamically-generated output from the header. This patch series can also be found at the following location on GitHub: https://github.com/joestringer/linux/tree/submit/bpf-command-docs_v2 Thanks also to Quentin Monnet for initial review. [0]: make -C tools/testing/selftests/bpf docs --- v2: * Remove build infrastructure in favor of kernel-doc directives * Shift userspace-api docs under Documentation/userspace-api/ebpf * Fix scripts/bpf_doc.py syscall --header (throw unsupported error) * Improve .gitignore handling of newly autogenerated files --- Joe Stringer (15): bpf: Import syscall arg documentation bpf: Add minimal bpf() command documentation bpf: Document BPF_F_LOCK in syscall commands bpf: Document BPF_PROG_PIN syscall command bpf: Document BPF_PROG_ATTACH syscall command bpf: Document BPF_PROG_TEST_RUN syscall command bpf: Document BPF_PROG_QUERY syscall command bpf: Document BPF_MAP_*_BATCH syscall commands scripts/bpf: Abstract eBPF API target parameter scripts/bpf: Add syscall commands printer tools/bpf: Remove bpf-helpers from bpftool docs selftests/bpf: Templatize man page generation selftests/bpf: Test syscall command parsing docs/bpf: Add bpf() syscall command reference tools: Sync uapi bpf.h header with latest changes Documentation/bpf/index.rst | 9 +- Documentation/userspace-api/ebpf/index.rst | 17 + Documentation/userspace-api/ebpf/syscall.rst | 24 + Documentation/userspace-api/index.rst | 1 + MAINTAINERS | 2 + include/uapi/linux/bpf.h | 714 +++++++++++++++++- scripts/{bpf_helpers_doc.py => bpf_doc.py} | 191 ++++- tools/bpf/Makefile.helpers | 60 -- tools/bpf/bpftool/.gitignore | 1 - tools/bpf/bpftool/Documentation/Makefile | 11 +- tools/include/uapi/linux/bpf.h | 714 +++++++++++++++++- tools/lib/bpf/Makefile | 2 +- tools/perf/MANIFEST | 2 +- tools/testing/selftests/bpf/.gitignore | 2 + tools/testing/selftests/bpf/Makefile | 20 +- tools/testing/selftests/bpf/Makefile.docs | 82 ++ .../selftests/bpf/test_bpftool_build.sh | 21 - tools/testing/selftests/bpf/test_doc_build.sh | 13 + 18 files changed, 1746 insertions(+), 140 deletions(-) create mode 100644 Documentation/userspace-api/ebpf/index.rst create mode 100644 Documentation/userspace-api/ebpf/syscall.rst rename scripts/{bpf_helpers_doc.py => bpf_doc.py} (82%) delete mode 100644 tools/bpf/Makefile.helpers create mode 100644 tools/testing/selftests/bpf/Makefile.docs create mode 100755 tools/testing/selftests/bpf/test_doc_build.sh -- 2.27.0
