linux/Documentation/bpf/maps.rst
Christoph Hellwig bc84e959e5 bpf, docs: Move handling of maps to Documentation/bpf/maps.rst
Move the general maps documentation into the maps.rst file from the
overall networking filter documentation and add a link instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211119163215.971383-5-hch@lst.de
2021-11-30 10:52:11 -08:00

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=========
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_*