netdev - Re: [PATCH bpf-next v4 00/10] bpf: document eBPF helpers and add a script to generate man page

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Date:   Fri, 27 Apr 2018 11:08:34 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Quentin Monnet <quentin.monnet@...ronome.com>, ast@...nel.org
Cc:     netdev@...r.kernel.org, oss-drivers@...ronome.com,
        linux-doc@...r.kernel.org, linux-man@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 00/10] bpf: document eBPF helpers and add a
 script to generate man page

On 04/25/2018 07:16 PM, Quentin Monnet wrote:
> 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 somewhat outdated and not complete.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.
[...]

Applied yesterday night to bpf-next (and now in net-next), thanks Quentin!