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d2b497a973
Improve the grammar of the function descriptions and highlight
that the key is a socket fd.
Fixes: f3212ad5b7
("docs/bpf: Add documentation for BPF_MAP_TYPE_SK_STORAGE")
Reported-by: Martin KaFai Lau <martin.lau@linux.dev>
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20221212101600.56026-1-donald.hunter@gmail.com
160 lines
4.9 KiB
ReStructuredText
160 lines
4.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-only
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.. Copyright (C) 2022 Red Hat, Inc.
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=======================
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BPF_MAP_TYPE_SK_STORAGE
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=======================
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.. note::
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- ``BPF_MAP_TYPE_SK_STORAGE`` was introduced in kernel version 5.2
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``BPF_MAP_TYPE_SK_STORAGE`` is used to provide socket-local storage for BPF
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programs. A map of type ``BPF_MAP_TYPE_SK_STORAGE`` declares the type of storage
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to be provided and acts as the handle for accessing the socket-local
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storage. The values for maps of type ``BPF_MAP_TYPE_SK_STORAGE`` are stored
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locally with each socket instead of with the map. The kernel is responsible for
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allocating storage for a socket when requested and for freeing the storage when
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either the map or the socket is deleted.
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.. note::
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- The key type must be ``int`` and ``max_entries`` must be set to ``0``.
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- The ``BPF_F_NO_PREALLOC`` flag must be used when creating a map for
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socket-local storage.
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Usage
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=====
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Kernel BPF
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----------
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bpf_sk_storage_get()
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~~~~~~~~~~~~~~~~~~~~
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.. code-block:: c
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void *bpf_sk_storage_get(struct bpf_map *map, void *sk, void *value, u64 flags)
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Socket-local storage for ``map`` can be retrieved from socket ``sk`` using the
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``bpf_sk_storage_get()`` helper. If the ``BPF_LOCAL_STORAGE_GET_F_CREATE``
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flag is used then ``bpf_sk_storage_get()`` will create the storage for ``sk``
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if it does not already exist. ``value`` can be used together with
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``BPF_LOCAL_STORAGE_GET_F_CREATE`` to initialize the storage value, otherwise
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it will be zero initialized. Returns a pointer to the storage on success, or
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``NULL`` in case of failure.
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.. note::
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- ``sk`` is a kernel ``struct sock`` pointer for LSM or tracing programs.
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- ``sk`` is a ``struct bpf_sock`` pointer for other program types.
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bpf_sk_storage_delete()
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~~~~~~~~~~~~~~~~~~~~~~~
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.. code-block:: c
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long bpf_sk_storage_delete(struct bpf_map *map, void *sk)
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Socket-local storage for ``map`` can be deleted from socket ``sk`` using the
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``bpf_sk_storage_delete()`` helper. Returns ``0`` on success, or negative
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error in case of failure.
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User space
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----------
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bpf_map_update_elem()
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~~~~~~~~~~~~~~~~~~~~~
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.. code-block:: c
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int bpf_map_update_elem(int map_fd, const void *key, const void *value, __u64 flags)
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Socket-local storage for map ``map_fd`` can be added or updated locally to a
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socket using the ``bpf_map_update_elem()`` libbpf function. The socket is
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identified by a `socket` ``fd`` stored in the pointer ``key``. The pointer
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``value`` has the data to be added or updated to the socket ``fd``. The type
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and size of ``value`` should be the same as the value type of the map
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definition.
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The ``flags`` parameter can be used to control the update behaviour:
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- ``BPF_ANY`` will create storage for `socket` ``fd`` or update existing storage.
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- ``BPF_NOEXIST`` will create storage for `socket` ``fd`` only if it did not
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already exist, otherwise the call will fail with ``-EEXIST``.
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- ``BPF_EXIST`` will update existing storage for `socket` ``fd`` if it already
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exists, otherwise the call will fail with ``-ENOENT``.
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Returns ``0`` on success, or negative error in case of failure.
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bpf_map_lookup_elem()
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~~~~~~~~~~~~~~~~~~~~~
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.. code-block:: c
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int bpf_map_lookup_elem(int map_fd, const void *key, void *value)
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Socket-local storage for map ``map_fd`` can be retrieved from a socket using
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the ``bpf_map_lookup_elem()`` libbpf function. The storage is retrieved from
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the socket identified by a `socket` ``fd`` stored in the pointer
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``key``. Returns ``0`` on success, or negative error in case of failure.
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bpf_map_delete_elem()
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~~~~~~~~~~~~~~~~~~~~~
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.. code-block:: c
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int bpf_map_delete_elem(int map_fd, const void *key)
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Socket-local storage for map ``map_fd`` can be deleted from a socket using the
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``bpf_map_delete_elem()`` libbpf function. The storage is deleted from the
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socket identified by a `socket` ``fd`` stored in the pointer ``key``. Returns
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``0`` on success, or negative error in case of failure.
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Examples
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========
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Kernel BPF
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----------
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This snippet shows how to declare socket-local storage in a BPF program:
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.. code-block:: c
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struct {
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__uint(type, BPF_MAP_TYPE_SK_STORAGE);
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__uint(map_flags, BPF_F_NO_PREALLOC);
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__type(key, int);
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__type(value, struct my_storage);
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} socket_storage SEC(".maps");
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This snippet shows how to retrieve socket-local storage in a BPF program:
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.. code-block:: c
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SEC("sockops")
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int _sockops(struct bpf_sock_ops *ctx)
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{
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struct my_storage *storage;
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struct bpf_sock *sk;
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sk = ctx->sk;
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if (!sk)
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return 1;
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storage = bpf_sk_storage_get(&socket_storage, sk, 0,
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BPF_LOCAL_STORAGE_GET_F_CREATE);
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if (!storage)
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return 1;
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/* Use 'storage' here */
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return 1;
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}
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Please see the ``tools/testing/selftests/bpf`` directory for functional
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examples.
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References
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==========
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https://lwn.net/ml/netdev/20190426171103.61892-1-kafai@fb.com/
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