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1.. SPDX-License-Identifier: GPL-2.0-only2.. Copyright (C) 2022 Red Hat, Inc.3 4=======================5BPF_MAP_TYPE_SK_STORAGE6=======================7 8.. note::9 - ``BPF_MAP_TYPE_SK_STORAGE`` was introduced in kernel version 5.210 11``BPF_MAP_TYPE_SK_STORAGE`` is used to provide socket-local storage for BPF12programs. A map of type ``BPF_MAP_TYPE_SK_STORAGE`` declares the type of storage13to be provided and acts as the handle for accessing the socket-local14storage. The values for maps of type ``BPF_MAP_TYPE_SK_STORAGE`` are stored15locally with each socket instead of with the map. The kernel is responsible for16allocating storage for a socket when requested and for freeing the storage when17either the map or the socket is deleted.18 19.. note::20 - The key type must be ``int`` and ``max_entries`` must be set to ``0``.21 - The ``BPF_F_NO_PREALLOC`` flag must be used when creating a map for22 socket-local storage.23 24Usage25=====26 27Kernel BPF28----------29 30bpf_sk_storage_get()31~~~~~~~~~~~~~~~~~~~~32 33.. code-block:: c34 35 void *bpf_sk_storage_get(struct bpf_map *map, void *sk, void *value, u64 flags)36 37Socket-local storage for ``map`` can be retrieved from socket ``sk`` using the38``bpf_sk_storage_get()`` helper. If the ``BPF_LOCAL_STORAGE_GET_F_CREATE``39flag is used then ``bpf_sk_storage_get()`` will create the storage for ``sk``40if it does not already exist. ``value`` can be used together with41``BPF_LOCAL_STORAGE_GET_F_CREATE`` to initialize the storage value, otherwise42it will be zero initialized. Returns a pointer to the storage on success, or43``NULL`` in case of failure.44 45.. note::46 - ``sk`` is a kernel ``struct sock`` pointer for LSM or tracing programs.47 - ``sk`` is a ``struct bpf_sock`` pointer for other program types.48 49bpf_sk_storage_delete()50~~~~~~~~~~~~~~~~~~~~~~~51 52.. code-block:: c53 54 long bpf_sk_storage_delete(struct bpf_map *map, void *sk)55 56Socket-local storage for ``map`` can be deleted from socket ``sk`` using the57``bpf_sk_storage_delete()`` helper. Returns ``0`` on success, or negative58error in case of failure.59 60User space61----------62 63bpf_map_update_elem()64~~~~~~~~~~~~~~~~~~~~~65 66.. code-block:: c67 68 int bpf_map_update_elem(int map_fd, const void *key, const void *value, __u64 flags)69 70Socket-local storage for map ``map_fd`` can be added or updated locally to a71socket using the ``bpf_map_update_elem()`` libbpf function. The socket is72identified by a `socket` ``fd`` stored in the pointer ``key``. The pointer73``value`` has the data to be added or updated to the socket ``fd``. The type74and size of ``value`` should be the same as the value type of the map75definition.76 77The ``flags`` parameter can be used to control the update behaviour:78 79- ``BPF_ANY`` will create storage for `socket` ``fd`` or update existing storage.80- ``BPF_NOEXIST`` will create storage for `socket` ``fd`` only if it did not81 already exist, otherwise the call will fail with ``-EEXIST``.82- ``BPF_EXIST`` will update existing storage for `socket` ``fd`` if it already83 exists, otherwise the call will fail with ``-ENOENT``.84 85Returns ``0`` on success, or negative error in case of failure.86 87bpf_map_lookup_elem()88~~~~~~~~~~~~~~~~~~~~~89 90.. code-block:: c91 92 int bpf_map_lookup_elem(int map_fd, const void *key, void *value)93 94Socket-local storage for map ``map_fd`` can be retrieved from a socket using95the ``bpf_map_lookup_elem()`` libbpf function. The storage is retrieved from96the socket identified by a `socket` ``fd`` stored in the pointer97``key``. Returns ``0`` on success, or negative error in case of failure.98 99bpf_map_delete_elem()100~~~~~~~~~~~~~~~~~~~~~101 102.. code-block:: c103 104 int bpf_map_delete_elem(int map_fd, const void *key)105 106Socket-local storage for map ``map_fd`` can be deleted from a socket using the107``bpf_map_delete_elem()`` libbpf function. The storage is deleted from the108socket identified by a `socket` ``fd`` stored in the pointer ``key``. Returns109``0`` on success, or negative error in case of failure.110 111Examples112========113 114Kernel BPF115----------116 117This snippet shows how to declare socket-local storage in a BPF program:118 119.. code-block:: c120 121 struct {122 __uint(type, BPF_MAP_TYPE_SK_STORAGE);123 __uint(map_flags, BPF_F_NO_PREALLOC);124 __type(key, int);125 __type(value, struct my_storage);126 } socket_storage SEC(".maps");127 128This snippet shows how to retrieve socket-local storage in a BPF program:129 130.. code-block:: c131 132 SEC("sockops")133 int _sockops(struct bpf_sock_ops *ctx)134 {135 struct my_storage *storage;136 struct bpf_sock *sk;137 138 sk = ctx->sk;139 if (!sk)140 return 1;141 142 storage = bpf_sk_storage_get(&socket_storage, sk, 0,143 BPF_LOCAL_STORAGE_GET_F_CREATE);144 if (!storage)145 return 1;146 147 /* Use 'storage' here */148 149 return 1;150 }151 152 153Please see the ``tools/testing/selftests/bpf`` directory for functional154examples.155 156References157==========158 159https://lwn.net/ml/netdev/20190426171103.61892-1-kafai@fb.com/160