Re: [PATCH bpf-next v4] docs/bpf: Add documentation for BPF_MAP_TYPE_SK_STORAGE

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On 12/9/22 3:24 AM, Donald Hunter wrote:
Add documentation for the BPF_MAP_TYPE_SK_STORAGE including
kernel version introduced, usage and examples.

Thanks for writing the doc for sk_storage!

+User space
+----------
+
+bpf_map_update_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+   int bpf_map_update_elem(int map_fd, const void *key, const void *value, __u64 flags)
+
+Socket-local storage for the socket identified by ``key`` belonging to
+``map_fd`` can be added or updated using the ``bpf_map_update_elem()`` libbpf > +function. ``key`` must be a pointer to a valid ``fd`` in the user space
+program. The ``flags`` parameter can be used to control the update behaviour:

The "``key`` belonging to ``map_fd``" seems confusing. Also, it is useful to highlight the ``key`` is a _socket_ ``fd``.

May be something like:

A socket-local storage can be added/updated locally to a socket identified by a _socket_ ``fd`` stored in the pointer ``key``. The pointer ``value`` has the data to be added/updated to the socket ``fd``. The type and size of ``value`` should be the same as the value type of the map definition.

Feel free to rephrase the above in a better way.

+
+- ``BPF_ANY`` will create storage for ``fd`` or update existing storage.
+- ``BPF_NOEXIST`` will create storage for ``fd`` only if it did not already
+  exist, otherwise the call will fail with ``-EEXIST``.
+- ``BPF_EXIST`` will update existing storage for ``fd`` if it already exists,
+  otherwise the call will fail with ``-ENOENT``.
+
+Returns ``0`` on success, or negative error in case of failure.
+
+bpf_map_lookup_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+   int bpf_map_lookup_elem(int map_fd, const void *key, void *value)
+
+Socket-local storage for the socket identified by ``key`` belonging to
+``map_fd`` can be retrieved using the ``bpf_map_lookup_elem()`` libbpf
+function. ``key`` must be a pointer to a valid ``fd`` in the user space

Same here.

+program. Returns ``0`` on success, or negative error in case of failure.
+
+bpf_map_delete_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+   int bpf_map_delete_elem(int map_fd, const void *key)
+
+Socket-local storage for the socket identified by ``key`` belonging to
+``map_fd`` can be deleted using the ``bpf_map_delete_elem()`` libbpf
+function. Returns ``0`` on success, or negative error in case of failure.

Same here.




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