bpf, docs: Move handling of maps to Documentation/bpf/maps.rst

[linux-block.git] / Documentation / bpf / maps.rst

=========
eBPF maps
=========

'maps' is a generic storage of different types for sharing data between kernel
and userspace.

The maps are accessed from user space via BPF syscall, which has commands:

- create a map with given type and attributes
  ``map_fd = bpf(BPF_MAP_CREATE, union bpf_attr *attr, u32 size)``
  using attr->map_type, attr->key_size, attr->value_size, attr->max_entries
  returns process-local file descriptor or negative error

- lookup key in a given map
  ``err = bpf(BPF_MAP_LOOKUP_ELEM, union bpf_attr *attr, u32 size)``
  using attr->map_fd, attr->key, attr->value
  returns zero and stores found elem into value or negative error

- create or update key/value pair in a given map
  ``err = bpf(BPF_MAP_UPDATE_ELEM, union bpf_attr *attr, u32 size)``
  using attr->map_fd, attr->key, attr->value
  returns zero or negative error

- find and delete element by key in a given map
  ``err = bpf(BPF_MAP_DELETE_ELEM, union bpf_attr *attr, u32 size)``
  using attr->map_fd, attr->key

- to delete map: close(fd)
  Exiting process will delete maps automatically

userspace programs use this syscall to create/access maps that eBPF programs
are concurrently updating.

maps can have different types: hash, array, bloom filter, radix-tree, etc.

The map is defined by:

  - type
  - max number of elements
  - key size in bytes
  - value size in bytes

Map Types
=========

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

   map_*