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authorDaniel Borkmann <daniel@iogearbox.net>2018-04-27 00:22:00 +0200
committerDaniel Borkmann <daniel@iogearbox.net>2018-04-27 00:22:01 +0200
commita6712d45b03e89800e687873fd4af015f5aaf4dd (patch)
tree248d40cb6a9ab6a76dae24b92d1cfeaaee67b26b /samples
parent3f13de6d6f3cfabbc94e7e6495540cca46a8682f (diff)
parent9cde0c8892b9bba07b27f2317d8d02707dc6ff92 (diff)
downloadlinux-a6712d45b03e89800e687873fd4af015f5aaf4dd.tar.bz2
Merge branch 'bpf-uapi-helper-doc'
Quentin Monnet says: ==================== eBPF helper functions can be called from within eBPF programs to perform a variety of tasks that would be otherwise hard or impossible to do with eBPF itself. There is a growing number of such helper functions in the kernel, but documentation is scarce. The main user space header file does contain a short commented description of most helpers, but it is somewhat outdated and not complete. It is more a "cheat sheet" than a real documentation accessible to new eBPF developers. This commit attempts to improve the situation by replacing the existing overview for the helpers with a more developed description. Furthermore, a Python script is added to generate a manual page for eBPF helpers. The workflow is the following, and requires the rst2man utility: $ ./scripts/bpf_helpers_doc.py \ --filename include/uapi/linux/bpf.h > /tmp/bpf-helpers.rst $ rst2man /tmp/bpf-helpers.rst > /tmp/bpf-helpers.7 $ man /tmp/bpf-helpers.7 The objective is to keep all documentation related to the helpers in a single place, and to be able to generate from here a manual page that could be packaged in the man-pages repository and shipped with most distributions. Additionally, parsing the prototypes of the helper functions could hopefully be reused, with a different Printer object, to generate header files needed in some eBPF-related projects. Regarding the description of each helper, it comprises several items: - The function prototype. - A description of the function and of its arguments (except for a couple of cases, when there are no arguments and the return value makes the function usage really obvious). - A description of return values (if not void). Additional items such as the list of compatible eBPF program and map types for each helper, Linux kernel version that introduced the helper, GPL-only restriction, and commit hash could be added in the future, but it was decided on the mailing list to leave them aside for now. For several helpers, descriptions are inspired (at times, nearly copied) from the commit logs introducing them in the kernel--Many thanks to their respective authors! Some sentences were also adapted from comments from the reviews, thanks to the reviewers as well. Descriptions were completed as much as possible, the objective being to have something easily accessible even for people just starting with eBPF. There is probably a bit more work to do in this direction for some helpers. Some RST formatting is used in the descriptions (not in function prototypes, to keep them readable, but the Python script provided in order to generate the RST for the manual page does add formatting to prototypes, to produce something pretty) to get "bold" and "italics" in manual pages. Hopefully, the descriptions in bpf.h file remains perfectly readable. Note that the few trailing white spaces are intentional, removing them would break paragraphs for rst2man. The descriptions should ideally be updated each time someone adds a new helper, or updates the behaviour (new socket option supported, ...) or the interface (new flags available, ...) of existing ones. To ease the review process, the documentation has been split into several patches. v3 -> v4: - Add a patch (#9) for newly added BPF helpers. - Add a patch (#10) to update UAPI bpf.h version under tools/. - Use SPDX tag in Python script. - Several fixes on man page header and footer, and helpers documentation. Please refer to individual patches for details. RFC v2 -> PATCH v3: Several fixes on man page header and footer, and helpers documentation. Please refer to individual patches for details. RFC v1 -> RFC v2: - Remove "For" (compatible program and map types), "Since" (minimal Linux kernel version required), "GPL only" sections and commit hashes for the helpers. - Add comment on top of the description list to explain how this documentation is supposed to be processed. - Update Python script accordingly (remove the same sections, and remove paragraphs on program types and GPL restrictions from man page header). - Split series into several patches. ==================== Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Cc: linux-doc@vger.kernel.org Cc: linux-man@vger.kernel.org
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