Provide user documentation about sockopt prog type and cgroup hooks.
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
---
Documentation/bpf/index.rst | 1 +
Documentation/bpf/prog_cgroup_sockopt.rst | 42 +++++++++++++++++++++++
2 files changed, 43 insertions(+)
create mode 100644 Documentation/bpf/prog_cgroup_sockopt.rst
diff --git a/Documentation/bpf/index.rst b/Documentation/bpf/index.rst
index d3fe4cac0c90..801a6ed3f2e5 100644
--- a/Documentation/bpf/index.rst
+++ b/Documentation/bpf/index.rst
@@ -42,6 +42,7 @@ Program types
.. toctree::
:maxdepth: 1
+ prog_cgroup_sockopt
prog_cgroup_sysctl
prog_flow_dissector
diff --git a/Documentation/bpf/prog_cgroup_sockopt.rst b/Documentation/bpf/prog_cgroup_sockopt.rst
new file mode 100644
index 000000000000..7e34ed0b59c0
--- /dev/null
+++ b/Documentation/bpf/prog_cgroup_sockopt.rst
@@ -0,0 +1,42 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+BPF_PROG_TYPE_SOCKOPT
+=====================
+
+``BPF_PROG_TYPE_SOCKOPT`` program type can be attached to two cgroup hooks:
+
+* ``BPF_CGROUP_GETSOCKOPT`` - called every time process executes ``getsockopt``
+ system call.
+* ``BPF_CGROUP_SETSOCKOPT`` - called every time process executes ``setsockopt``
+ system call.
+
+The context (``struct bpf_sockopt``) has associated socket (``sk``) and
+all input arguments: ``level``, ``optname``, ``optval`` and ``optlen``.
+
+By default, when the hook returns, kernel code that handles ``getsockopt``
+or ``setsockopt`` is executed as well. That way BPF code can handle a
+subset of options and let kernel handle the rest. To prevent kernel
+handlers to be executed, there is a new helper called
+``bpf_sockopt_handled()``. It tells kernel that BPF program has handled
+the socket option and control should be returned to userspace.
+
+BPF_CGROUP_SETSOCKOPT
+=====================
+
+``BPF_CGROUP_SETSOCKOPT`` has a read-only context and this hook has
+access to cgroup and socket local storage.
+
+BPF_CGROUP_GETSOCKOPT
+=====================
+
+``BPF_CGROUP_GETSOCKOPT`` has to fill in ``optval`` and adjust
+``optlen`` accordingly. Input ``optlen`` contains the maximum length
+of data that can be returned to the userspace. In other words, BPF
+program can't increase ``optlen``, it can only decrease it.
+
+Return Type
+===========
+
+* ``0`` - reject the syscall, ``EPERM`` will be returned to the userspace.
+* ``1`` - success.
--
2.22.0.rc1.311.g5d7573a151-goog
