======== BPF maps

BPF 'maps' provide generic storage of different types for sharing data between kernel and user space. There are several storage types available, including hash, array, bloom filter and radix-tree. Several of the map types exist to support specific BPF helpers that perform actions based on the map contents. The maps are accessed from BPF programs via BPF helpers which are documented in the man-pages_ for bpf-helpers(7)_.

BPF maps are accessed from user space via the bpf syscall, which provides commands to create maps, lookup elements, update elements and delete elements. More details of the BPF syscall are available in ebpf-syscall_ and in the man-pages_ for bpf(2)_.

Map Types

.. toctree:: :maxdepth: 1 :glob:

map_*

Usage Notes

.. c:function:: int bpf(int command, union bpf_attr *attr, u32 size)

Use the bpf() system call to perform the operation specified by command. The operation takes parameters provided in attr. The size argument is the size of the union bpf_attr in attr.

BPF_MAP_CREATE

Create a map with the desired type and attributes in attr:

.. code-block:: c

int fd;
union bpf_attr attr = {
        .map_type = BPF_MAP_TYPE_ARRAY;  /* mandatory */
        .key_size = sizeof(__u32);       /* mandatory */
        .value_size = sizeof(__u32);     /* mandatory */
        .max_entries = 256;              /* mandatory */
        .map_flags = BPF_F_MMAPABLE;
        .map_name = "example_array";
};

fd = bpf(BPF_MAP_CREATE, &attr, sizeof(attr));

Returns a process-local file descriptor on success, or negative error in case of failure. The map can be deleted by calling close(fd). Maps held by open file descriptors will be deleted automatically when a process exits.

.. note:: Valid characters for map_name are A-Z, a-z, 0-9, '_' and '.'.

BPF_MAP_LOOKUP_ELEM

Lookup key in a given map using attr->map_fd, attr->key, attr->value. Returns zero and stores found elem into attr->value on success, or negative error on failure.

BPF_MAP_UPDATE_ELEM

Create or update key/value pair in a given map using attr->map_fd, attr->key, attr->value. Returns zero on success or negative error on failure.

BPF_MAP_DELETE_ELEM

Find and delete element by key in a given map using attr->map_fd, attr->key. Returns zero on success or negative error on failure.

.. Links: .. _man-pages: https://www.kernel.org/doc/man-pages/ .. _bpf(2): https://man7.org/linux/man-pages/man2/bpf.2.html .. _bpf-helpers(7): https://man7.org/linux/man-pages/man7/bpf-helpers.7.html .. _ebpf-syscall: https://docs.kernel.org/userspace-api/ebpf/syscall.html