bpf: Document BPF_PROG_TYPE_CGROUP_SYSCTL

Add documentation for BPF_PROG_TYPE_CGROUP_SYSCTL, including general
info, attach type, context, return code, helpers, example and usage
considerations.

A separate file prog_cgroup_sysctl.rst is added to Documentation/bpf/.

In the future more program types can be documented in their own
prog_<name>.rst files.

Another way to place program type specific documentation would be to
group program types somehow (e.g. cgroup.rst for all cgroup-bpf
programs), but it may not scale well since some program types may belong
to different groups, e.g. BPF_PROG_TYPE_CGROUP_SKB can be documented
together with either cgroup-bpf programs or programs that access skb.

The new file is added to the index and verified by `make htmldocs` /
sanity-check by lynx.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/bpf/index.rst b/Documentation/bpf/index.rst
index 4e77932959cc..dadcaa9a9f5f 100644
--- a/Documentation/bpf/index.rst
+++ b/Documentation/bpf/index.rst
@@ -36,6 +36,15 @@ Two sets of Questions and Answers (Q&A) are maintained.
    bpf_devel_QA
 
 
+Program types
+=============
+
+.. toctree::
+   :maxdepth: 1
+
+   prog_cgroup_sysctl
+
+
 .. Links:
 .. _Documentation/networking/filter.txt: ../networking/filter.txt
 .. _man-pages: https://www.kernel.org/doc/man-pages/