docs/bpf: Fix sphinx warnings in BPF map docs

Fix duplicate C declaration warnings when using sphinx >= 3.1.
Reported-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/bpf/ed4dac84-1b12-5c58-e4de-93ab9ac67c09@gmail.com
Link: https://lore.kernel.org/bpf/20221122143933.91321-1-donald.hunter@gmail.com

Documentation/bpf/map_array.rst

@@ -32,7 +32,11 @@ Usage
 Kernel BPF
 ----------
 
-.. c:function::
+bpf_map_lookup_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
 
 Array elements can be retrieved using the ``bpf_map_lookup_elem()`` helper.
@@ -40,7 +44,11 @@ This helper returns a pointer into the array element, so to avoid data races
 with userspace reading the value, the user must use primitives like
 ``__sync_fetch_and_add()`` when updating the value in-place.
 
-.. c:function::
+bpf_map_update_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags)
 
 Array elements can be updated using the ``bpf_map_update_elem()`` helper.
@@ -53,7 +61,7 @@ To clear an array element, you may use ``bpf_map_update_elem()`` to insert a
 zero value to that index.
 
 Per CPU Array
-~~~~~~~~~~~~~
+-------------
 
 Values stored in ``BPF_MAP_TYPE_ARRAY`` can be accessed by multiple programs
 across different CPUs. To restrict storage to a single CPU, you may use a
@@ -63,7 +71,11 @@ When using a ``BPF_MAP_TYPE_PERCPU_ARRAY`` the ``bpf_map_update_elem()`` and
 ``bpf_map_lookup_elem()`` helpers automatically access the slot for the current
 CPU.
 
-.. c:function::
+bpf_map_lookup_percpu_elem()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    void *bpf_map_lookup_percpu_elem(struct bpf_map *map, const void *key, u32 cpu)
 
 The ``bpf_map_lookup_percpu_elem()`` helper can be used to lookup the array

Documentation/bpf/map_hash.rst

@@ -34,7 +34,14 @@ the ``BPF_F_NO_COMMON_LRU`` flag when calling ``bpf_map_create``.
 Usage
 =====
 
-.. c:function::
+Kernel BPF
+----------
+
+bpf_map_update_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags)
 
 Hash entries can be added or updated using the ``bpf_map_update_elem()``
@@ -49,14 +56,22 @@ parameter can be used to control the update behaviour:
 ``bpf_map_update_elem()`` returns 0 on success, or negative error in
 case of failure.
 
-.. c:function::
+bpf_map_lookup_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
 
 Hash entries can be retrieved using the ``bpf_map_lookup_elem()``
 helper. This helper returns a pointer to the value associated with
 ``key``, or ``NULL`` if no entry was found.
 
-.. c:function::
+bpf_map_delete_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    long bpf_map_delete_elem(struct bpf_map *map, const void *key)
 
 Hash entries can be deleted using the ``bpf_map_delete_elem()``
@@ -70,7 +85,11 @@ For ``BPF_MAP_TYPE_PERCPU_HASH`` and ``BPF_MAP_TYPE_LRU_PERCPU_HASH``
 the ``bpf_map_update_elem()`` and ``bpf_map_lookup_elem()`` helpers
 automatically access the hash slot for the current CPU.
 
-.. c:function::
+bpf_map_lookup_percpu_elem()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    void *bpf_map_lookup_percpu_elem(struct bpf_map *map, const void *key, u32 cpu)
 
 The ``bpf_map_lookup_percpu_elem()`` helper can be used to lookup the
@@ -89,7 +108,11 @@ See ``tools/testing/selftests/bpf/progs/test_spin_lock.c``.
 Userspace
 ---------
 
-.. c:function::
+bpf_map_get_next_key()
+~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    int bpf_map_get_next_key(int fd, const void *cur_key, void *next_key)
 
 In userspace, it is possible to iterate through the keys of a hash using

Documentation/bpf/map_lpm_trie.rst

@@ -35,7 +35,11 @@ Usage
 Kernel BPF
 ----------
 
-.. c:function::
+bpf_map_lookup_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
 
 The longest prefix entry for a given data value can be found using the
@@ -48,7 +52,11 @@ performing longest prefix lookups. For example, when searching for the
 longest prefix match for an IPv4 address, ``prefixlen`` should be set to
 ``32``.
 
-.. c:function::
+bpf_map_update_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags)
 
 Prefix entries can be added or updated using the ``bpf_map_update_elem()``
@@ -61,7 +69,11 @@ case of failure.
     The flags parameter must be one of BPF_ANY, BPF_NOEXIST or BPF_EXIST,
     but the value is ignored, giving BPF_ANY semantics.
 
-.. c:function::
+bpf_map_delete_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    long bpf_map_delete_elem(struct bpf_map *map, const void *key)
 
 Prefix entries can be deleted using the ``bpf_map_delete_elem()``
@@ -74,7 +86,11 @@ Userspace
 Access from userspace uses libbpf APIs with the same names as above, with
 the map identified by ``fd``.
 
-.. c:function::
+bpf_map_get_next_key()
+~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    int bpf_map_get_next_key (int fd, const void *cur_key, void *next_key)
 
 A userspace program can iterate through the entries in an LPM trie using

Documentation/bpf/map_of_maps.rst

@@ -45,7 +45,11 @@ Usage
 Kernel BPF Helper
 -----------------
 
-.. c:function::
+bpf_map_lookup_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
 
 Inner maps can be retrieved using the ``bpf_map_lookup_elem()`` helper. This

Documentation/bpf/map_queue_stack.rst

@@ -28,7 +28,11 @@ Usage
 Kernel BPF
 ----------
 
-.. c:function::
+bpf_map_push_elem()
+~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    long bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)
 
 An element ``value`` can be added to a queue or stack using the
@@ -38,14 +42,22 @@ when the queue or stack is full, the oldest element will be removed to
 make room for ``value`` to be added. Returns ``0`` on success, or
 negative error in case of failure.
 
-.. c:function::
+bpf_map_peek_elem()
+~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    long bpf_map_peek_elem(struct bpf_map *map, void *value)
 
 This helper fetches an element ``value`` from a queue or stack without
 removing it. Returns ``0`` on success, or negative error in case of
 failure.
 
-.. c:function::
+bpf_map_pop_elem()
+~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    long bpf_map_pop_elem(struct bpf_map *map, void *value)
 
 This helper removes an element into ``value`` from a queue or
@@ -55,7 +67,11 @@ stack. Returns ``0`` on success, or negative error in case of failure.
 Userspace
 ---------
 
-.. c:function::
+bpf_map_update_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    int bpf_map_update_elem (int fd, const void *key, const void *value, __u64 flags)
 
 A userspace program can push ``value`` onto a queue or stack using libbpf's
@@ -64,7 +80,11 @@ A userspace program can push ``value`` onto a queue or stack using libbpf's
 same semantics as the ``bpf_map_push_elem`` kernel helper. Returns ``0`` on
 success, or negative error in case of failure.
 
-.. c:function::
+bpf_map_lookup_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    int bpf_map_lookup_elem (int fd, const void *key, void *value)
 
 A userspace program can peek at the ``value`` at the head of a queue or stack
@@ -72,7 +92,11 @@ using the libbpf ``bpf_map_lookup_elem`` function. The ``key`` parameter must be
 set to ``NULL``.  Returns ``0`` on success, or negative error in case of
 failure.
 
-.. c:function::
+bpf_map_lookup_and_delete_elem()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
    int bpf_map_lookup_and_delete_elem (int fd, const void *key, void *value)
 
 A userspace program can pop a ``value`` from the head of a queue or stack using