Add a more complete introduction, with links to man pages.
Move toctree of map types above usage notes.
Format usage notes to improve readability.
Signed-off-by: Donald Hunter <donald.hunter@xxxxxxxxx>
---
Documentation/bpf/maps.rst | 101 ++++++++++++++++++++++++-------------
1 file changed, 65 insertions(+), 36 deletions(-)
diff --git a/Documentation/bpf/maps.rst b/Documentation/bpf/maps.rst
index f41619e312ac..4906ff0f8382 100644
--- a/Documentation/bpf/maps.rst
+++ b/Documentation/bpf/maps.rst
@@ -1,52 +1,81 @@
-=========
-eBPF maps
+========
+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
+:doc:`/userspace-api/ebpf/syscall` and in the `man-pages`_ for `bpf(2)`_.
+
+Map Types
=========
-'maps' is a generic storage of different types for sharing data between kernel
-and userspace.
+.. toctree::
+ :maxdepth: 1
+ :glob:
-The maps are accessed from user space via BPF syscall, which has commands:
+ map_*
-- 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
+Usage Notes
+===========
-- 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
+.. c:function::
+ int bpf(int command, union bpf_attr *attr, u32 size)
-- 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
+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``.
-- 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
+**BPF_MAP_CREATE**
-- to delete map: close(fd)
- Exiting process will delete maps automatically
+Create a map with the desired type and attributes in ``attr``:
-userspace programs use this syscall to create/access maps that eBPF programs
-are concurrently updating.
+.. code-block:: c
-maps can have different types: hash, array, bloom filter, radix-tree, etc.
+ 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";
+ };
-The map is defined by:
+ fd = bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
- - type
- - max number of elements
- - key size in bytes
- - value size in bytes
+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.
-Map Types
-=========
+.. note:: Valid characters for ``map_name`` are ``A-Z``, ``a-z``, ``0-9``,
+ ``'_'`` and ``'.'``.
-.. toctree::
- :maxdepth: 1
- :glob:
+**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.
- map_*
\ No newline at end of file
+.. 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
--
2.35.1
