Documentation/bpf/map_devmap.rst - pub/scm/linux/kernel/git/tnguy/next-queue - Git at Google

 .. SPDX-License-Identifier: GPL-2.0-only
 .. Copyright (C) 2022 Red Hat, Inc.

 =================================================
 BPF_MAP_TYPE_DEVMAP and BPF_MAP_TYPE_DEVMAP_HASH
 =================================================

 .. note::
    - ``BPF_MAP_TYPE_DEVMAP`` was introduced in kernel version 4.14
    - ``BPF_MAP_TYPE_DEVMAP_HASH`` was introduced in kernel version 5.4

 ``BPF_MAP_TYPE_DEVMAP`` and ``BPF_MAP_TYPE_DEVMAP_HASH`` are BPF maps primarily
 used as backend maps for the XDP BPF helper call ``bpf_redirect_map()``.
 ``BPF_MAP_TYPE_DEVMAP`` is backed by an array that uses the key as
 the index to lookup a reference to a net device. While ``BPF_MAP_TYPE_DEVMAP_HASH``
 is backed by a hash table that uses a key to lookup a reference to a net device.
 The user provides either <``key``/ ``ifindex``> or <``key``/ ``struct bpf_devmap_val``>
 pairs to update the maps with new net devices.

 .. note::
     - The key to a hash map doesn't have to be an ``ifindex``.
     - While ``BPF_MAP_TYPE_DEVMAP_HASH`` allows for densely packing the net devices
       it comes at the cost of a hash of the key when performing a look up.

 The setup and packet enqueue/send code is shared between the two types of
 devmap; only the lookup and insertion is different.

 Usage
 =====
 Kernel BPF
 ----------
 bpf_redirect_map()
 ^^^^^^^^^^^^^^^^^^
 .. code-block:: c

     long bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)

 Redirect the packet to the endpoint referenced by ``map`` at index ``key``.
 For ``BPF_MAP_TYPE_DEVMAP`` and ``BPF_MAP_TYPE_DEVMAP_HASH`` this map contains
 references to net devices (for forwarding packets through other ports).

 The lower two bits of *flags* are used as the return code if the map lookup
 fails. This is so that the return value can be one of the XDP program return
 codes up to ``XDP_TX``, as chosen by the caller. The higher bits of ``flags``
 can be set to ``BPF_F_BROADCAST`` or ``BPF_F_EXCLUDE_INGRESS`` as defined
 below.

 With ``BPF_F_BROADCAST`` the packet will be broadcast to all the interfaces
 in the map, with ``BPF_F_EXCLUDE_INGRESS`` the ingress interface will be excluded
 from the broadcast.

 .. note::
     - The key is ignored if BPF_F_BROADCAST is set.
     - The broadcast feature can also be used to implement multicast forwarding:
       simply create multiple DEVMAPs, each one corresponding to a single multicast group.

 This helper will return ``XDP_REDIRECT`` on success, or the value of the two
 lower bits of the ``flags`` argument if the map lookup fails.

 More information about redirection can be found :doc:`redirect`

 bpf_map_lookup_elem()
 ^^^^^^^^^^^^^^^^^^^^^
 .. code-block:: c

    void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)

 Net device entries can be retrieved using the ``bpf_map_lookup_elem()``
 helper.

 User space
 ----------
 .. note::
     DEVMAP entries can only be updated/deleted from user space and not
     from an eBPF program. Trying to call these functions from a kernel eBPF
     program will result in the program failing to load and a verifier warning.

 bpf_map_update_elem()
 ^^^^^^^^^^^^^^^^^^^^^
 .. code-block:: c

    int bpf_map_update_elem(int fd, const void *key, const void *value, __u64 flags);

 Net device entries can be added or updated using the ``bpf_map_update_elem()``
 helper. This helper replaces existing elements atomically. The ``value`` parameter
 can be ``struct bpf_devmap_val`` or a simple ``int ifindex`` for backwards
 compatibility.

  .. code-block:: c

     struct bpf_devmap_val {
         __u32 ifindex;   /* device index */
         union {
             int   fd;  /* prog fd on map write */
             __u32 id;  /* prog id on map read */
         } bpf_prog;
     };

 The ``flags`` argument can be one of the following:
   - ``BPF_ANY``: Create a new element or update an existing element.
   - ``BPF_NOEXIST``: Create a new element only if it did not exist.
   - ``BPF_EXIST``: Update an existing element.

 DEVMAPs can associate a program with a device entry by adding a ``bpf_prog.fd``
 to ``struct bpf_devmap_val``. Programs are run after ``XDP_REDIRECT`` and have
 access to both Rx device and Tx device. The  program associated with the ``fd``
 must have type XDP with expected attach type ``xdp_devmap``.
 When a program is associated with a device index, the program is run on an
 ``XDP_REDIRECT`` and before the buffer is added to the per-cpu queue. Examples
 of how to attach/use xdp_devmap progs can be found in the kernel selftests:

 - ``tools/testing/selftests/bpf/prog_tests/xdp_devmap_attach.c``
 - ``tools/testing/selftests/bpf/progs/test_xdp_with_devmap_helpers.c``

 bpf_map_lookup_elem()
 ^^^^^^^^^^^^^^^^^^^^^
 .. code-block:: c

 .. c:function::
    int bpf_map_lookup_elem(int fd, const void *key, void *value);

 Net device entries can be retrieved using the ``bpf_map_lookup_elem()``
 helper.

 bpf_map_delete_elem()
 ^^^^^^^^^^^^^^^^^^^^^
 .. code-block:: c

 .. c:function::
    int bpf_map_delete_elem(int fd, const void *key);

 Net device entries can be deleted using the ``bpf_map_delete_elem()``
 helper. This helper will return 0 on success, or negative error in case of
 failure.

 Examples
 ========

 Kernel BPF
 ----------

 The following code snippet shows how to declare a ``BPF_MAP_TYPE_DEVMAP``
 called tx_port.

 .. code-block:: c

     struct {
         __uint(type, BPF_MAP_TYPE_DEVMAP);
         __type(key, __u32);
         __type(value, __u32);
         __uint(max_entries, 256);
     } tx_port SEC(".maps");

 The following code snippet shows how to declare a ``BPF_MAP_TYPE_DEVMAP_HASH``
 called forward_map.

 .. code-block:: c

     struct {
         __uint(type, BPF_MAP_TYPE_DEVMAP_HASH);
         __type(key, __u32);
         __type(value, struct bpf_devmap_val);
         __uint(max_entries, 32);
     } forward_map SEC(".maps");

 .. note::

     The value type in the DEVMAP above is a ``struct bpf_devmap_val``

 The following code snippet shows a simple xdp_redirect_map program. This program
 would work with a user space program that populates the devmap ``forward_map`` based
 on ingress ifindexes. The BPF program (below) is redirecting packets using the
 ingress ``ifindex`` as the ``key``.

 .. code-block:: c

     SEC("xdp")
     int xdp_redirect_map_func(struct xdp_md *ctx)
     {
         int index = ctx->ingress_ifindex;

         return bpf_redirect_map(&forward_map, index, 0);
     }

 The following code snippet shows a BPF program that is broadcasting packets to
 all the interfaces in the ``tx_port`` devmap.

 .. code-block:: c

     SEC("xdp")
     int xdp_redirect_map_func(struct xdp_md *ctx)
     {
         return bpf_redirect_map(&tx_port, 0, BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS);
     }

 User space
 ----------

 The following code snippet shows how to update a devmap called ``tx_port``.

 .. code-block:: c

     int update_devmap(int ifindex, int redirect_ifindex)
     {
         int ret;

         ret = bpf_map_update_elem(bpf_map__fd(tx_port), &ifindex, &redirect_ifindex, 0);
         if (ret < 0) {
             fprintf(stderr, "Failed to update devmap_ value: %s\n",
                 strerror(errno));
         }

         return ret;
     }

 The following code snippet shows how to update a hash_devmap called ``forward_map``.

 .. code-block:: c

     int update_devmap(int ifindex, int redirect_ifindex)
     {
         struct bpf_devmap_val devmap_val = { .ifindex = redirect_ifindex };
         int ret;

         ret = bpf_map_update_elem(bpf_map__fd(forward_map), &ifindex, &devmap_val, 0);
         if (ret < 0) {
             fprintf(stderr, "Failed to update devmap_ value: %s\n",
                 strerror(errno));
         }
         return ret;
     }

 References
 ===========

 - https://lwn.net/Articles/728146/
 - https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=6f9d451ab1a33728adb72d7ff66a7b374d665176
 - https://elixir.bootlin.com/linux/latest/source/net/core/filter.c#L4106
	.. SPDX-License-Identifier: GPL-2.0-only
	.. Copyright (C) 2022 Red Hat, Inc.

	=================================================
	BPF_MAP_TYPE_DEVMAP and BPF_MAP_TYPE_DEVMAP_HASH
	=================================================

	.. note::
	- ``BPF_MAP_TYPE_DEVMAP`` was introduced in kernel version 4.14
	- ``BPF_MAP_TYPE_DEVMAP_HASH`` was introduced in kernel version 5.4

	``BPF_MAP_TYPE_DEVMAP`` and ``BPF_MAP_TYPE_DEVMAP_HASH`` are BPF maps primarily
	used as backend maps for the XDP BPF helper call ``bpf_redirect_map()``.
	``BPF_MAP_TYPE_DEVMAP`` is backed by an array that uses the key as
	the index to lookup a reference to a net device. While ``BPF_MAP_TYPE_DEVMAP_HASH``
	is backed by a hash table that uses a key to lookup a reference to a net device.
	The user provides either <``key``/ ``ifindex``> or <``key``/ ``struct bpf_devmap_val``>
	pairs to update the maps with new net devices.

	.. note::
	- The key to a hash map doesn't have to be an ``ifindex``.
	- While ``BPF_MAP_TYPE_DEVMAP_HASH`` allows for densely packing the net devices
	it comes at the cost of a hash of the key when performing a look up.

	The setup and packet enqueue/send code is shared between the two types of
	devmap; only the lookup and insertion is different.

	Usage
	=====
	Kernel BPF
	----------
	bpf_redirect_map()
	^^^^^^^^^^^^^^^^^^
	.. code-block:: c

	long bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)

	Redirect the packet to the endpoint referenced by ``map`` at index ``key``.
	For ``BPF_MAP_TYPE_DEVMAP`` and ``BPF_MAP_TYPE_DEVMAP_HASH`` this map contains
	references to net devices (for forwarding packets through other ports).

	The lower two bits of flags are used as the return code if the map lookup
	fails. This is so that the return value can be one of the XDP program return
	codes up to ``XDP_TX``, as chosen by the caller. The higher bits of ``flags``
	can be set to ``BPF_F_BROADCAST`` or ``BPF_F_EXCLUDE_INGRESS`` as defined
	below.

	With ``BPF_F_BROADCAST`` the packet will be broadcast to all the interfaces
	in the map, with ``BPF_F_EXCLUDE_INGRESS`` the ingress interface will be excluded
	from the broadcast.

	.. note::
	- The key is ignored if BPF_F_BROADCAST is set.
	- The broadcast feature can also be used to implement multicast forwarding:
	simply create multiple DEVMAPs, each one corresponding to a single multicast group.

	This helper will return ``XDP_REDIRECT`` on success, or the value of the two
	lower bits of the ``flags`` argument if the map lookup fails.

	More information about redirection can be found :doc:`redirect`

	bpf_map_lookup_elem()
	^^^^^^^^^^^^^^^^^^^^^
	.. code-block:: c

	void bpf_map_lookup_elem(struct bpf_map map, const void *key)

	Net device entries can be retrieved using the ``bpf_map_lookup_elem()``
	helper.

	User space
	----------
	.. note::
	DEVMAP entries can only be updated/deleted from user space and not
	from an eBPF program. Trying to call these functions from a kernel eBPF
	program will result in the program failing to load and a verifier warning.

	bpf_map_update_elem()
	^^^^^^^^^^^^^^^^^^^^^
	.. code-block:: c

	int bpf_map_update_elem(int fd, const void key, const void value, __u64 flags);

	Net device entries can be added or updated using the ``bpf_map_update_elem()``
	helper. This helper replaces existing elements atomically. The ``value`` parameter
	can be ``struct bpf_devmap_val`` or a simple ``int ifindex`` for backwards
	compatibility.

	.. code-block:: c

	struct bpf_devmap_val {
	__u32 ifindex; /* device index */
	union {
	int fd; /* prog fd on map write */
	__u32 id; /* prog id on map read */
	} bpf_prog;
	};

	The ``flags`` argument can be one of the following:
	- ``BPF_ANY``: Create a new element or update an existing element.
	- ``BPF_NOEXIST``: Create a new element only if it did not exist.
	- ``BPF_EXIST``: Update an existing element.

	DEVMAPs can associate a program with a device entry by adding a ``bpf_prog.fd``
	to ``struct bpf_devmap_val``. Programs are run after ``XDP_REDIRECT`` and have
	access to both Rx device and Tx device. The program associated with the ``fd``
	must have type XDP with expected attach type ``xdp_devmap``.
	When a program is associated with a device index, the program is run on an
	``XDP_REDIRECT`` and before the buffer is added to the per-cpu queue. Examples
	of how to attach/use xdp_devmap progs can be found in the kernel selftests:

	- ``tools/testing/selftests/bpf/prog_tests/xdp_devmap_attach.c``
	- ``tools/testing/selftests/bpf/progs/test_xdp_with_devmap_helpers.c``

	bpf_map_lookup_elem()
	^^^^^^^^^^^^^^^^^^^^^
	.. code-block:: c

	.. c:function::
	int bpf_map_lookup_elem(int fd, const void key, void value);

	Net device entries can be retrieved using the ``bpf_map_lookup_elem()``
	helper.

	bpf_map_delete_elem()
	^^^^^^^^^^^^^^^^^^^^^
	.. code-block:: c

	.. c:function::
	int bpf_map_delete_elem(int fd, const void *key);

	Net device entries can be deleted using the ``bpf_map_delete_elem()``
	helper. This helper will return 0 on success, or negative error in case of
	failure.

	Examples
	========

	Kernel BPF
	----------

	The following code snippet shows how to declare a ``BPF_MAP_TYPE_DEVMAP``
	called tx_port.

	.. code-block:: c

	struct {
	__uint(type, BPF_MAP_TYPE_DEVMAP);
	__type(key, __u32);
	__type(value, __u32);
	__uint(max_entries, 256);
	} tx_port SEC(".maps");

	The following code snippet shows how to declare a ``BPF_MAP_TYPE_DEVMAP_HASH``
	called forward_map.

	.. code-block:: c

	struct {
	__uint(type, BPF_MAP_TYPE_DEVMAP_HASH);
	__type(key, __u32);
	__type(value, struct bpf_devmap_val);
	__uint(max_entries, 32);
	} forward_map SEC(".maps");

	.. note::

	The value type in the DEVMAP above is a ``struct bpf_devmap_val``

	The following code snippet shows a simple xdp_redirect_map program. This program
	would work with a user space program that populates the devmap ``forward_map`` based
	on ingress ifindexes. The BPF program (below) is redirecting packets using the
	ingress ``ifindex`` as the ``key``.

	.. code-block:: c

	SEC("xdp")
	int xdp_redirect_map_func(struct xdp_md *ctx)
	{
	int index = ctx->ingress_ifindex;

	return bpf_redirect_map(&forward_map, index, 0);
	}

	The following code snippet shows a BPF program that is broadcasting packets to
	all the interfaces in the ``tx_port`` devmap.

	.. code-block:: c

	SEC("xdp")
	int xdp_redirect_map_func(struct xdp_md *ctx)
	{
	return bpf_redirect_map(&tx_port, 0, BPF_F_BROADCAST \| BPF_F_EXCLUDE_INGRESS);
	}

	User space
	----------

	The following code snippet shows how to update a devmap called ``tx_port``.

	.. code-block:: c

	int update_devmap(int ifindex, int redirect_ifindex)
	{
	int ret;

	ret = bpf_map_update_elem(bpf_map__fd(tx_port), &ifindex, &redirect_ifindex, 0);
	if (ret < 0) {
	fprintf(stderr, "Failed to update devmap_ value: %s\n",
	strerror(errno));
	}

	return ret;
	}

	The following code snippet shows how to update a hash_devmap called ``forward_map``.

	.. code-block:: c

	int update_devmap(int ifindex, int redirect_ifindex)
	{
	struct bpf_devmap_val devmap_val = { .ifindex = redirect_ifindex };
	int ret;

	ret = bpf_map_update_elem(bpf_map__fd(forward_map), &ifindex, &devmap_val, 0);
	if (ret < 0) {
	fprintf(stderr, "Failed to update devmap_ value: %s\n",
	strerror(errno));
	}
	return ret;
	}

	References
	===========

	- https://lwn.net/Articles/728146/
	- https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=6f9d451ab1a33728adb72d7ff66a7b374d665176
	- https://elixir.bootlin.com/linux/latest/source/net/core/filter.c#L4106