1 1
2 ======== !! 2 =========
3 BPF maps !! 3 eBPF maps
4 ======== <<
5 <<
6 BPF 'maps' provide generic storage of differen <<
7 kernel and user space. There are several stora <<
8 hash, array, bloom filter and radix-tree. Seve <<
9 support specific BPF helpers that perform acti <<
10 maps are accessed from BPF programs via BPF he <<
11 `man-pages`_ for `bpf-helpers(7)`_. <<
12 <<
13 BPF maps are accessed from user space via the <<
14 commands to create maps, lookup elements, upda <<
15 More details of the BPF syscall are available <<
16 `man-pages`_ for `bpf(2)`_. <<
17 <<
18 Map Types <<
19 ========= 4 =========
20 5
21 .. toctree:: !! 6 'maps' is a generic storage of different types for sharing data between kernel
22 :maxdepth: 1 !! 7 and userspace.
23 :glob: <<
24 <<
25 map_* <<
26 <<
27 Usage Notes <<
28 =========== <<
29 <<
30 .. c:function:: <<
31 int bpf(int command, union bpf_attr *attr, <<
32 <<
33 Use the ``bpf()`` system call to perform the o <<
34 ``command``. The operation takes parameters pr <<
35 argument is the size of the ``union bpf_attr`` <<
36 <<
37 **BPF_MAP_CREATE** <<
38 8
39 Create a map with the desired type and attribu !! 9 The maps are accessed from user space via BPF syscall, which has commands:
40 10
41 .. code-block:: c !! 11 - create a map with given type and attributes
>> 12 ``map_fd = bpf(BPF_MAP_CREATE, union bpf_attr *attr, u32 size)``
>> 13 using attr->map_type, attr->key_size, attr->value_size, attr->max_entries
>> 14 returns process-local file descriptor or negative error
42 15
43 int fd; !! 16 - lookup key in a given map
44 union bpf_attr attr = { !! 17 ``err = bpf(BPF_MAP_LOOKUP_ELEM, union bpf_attr *attr, u32 size)``
45 .map_type = BPF_MAP_TYPE_ARRAY; / !! 18 using attr->map_fd, attr->key, attr->value
46 .key_size = sizeof(__u32); / !! 19 returns zero and stores found elem into value or negative error
47 .value_size = sizeof(__u32); / <<
48 .max_entries = 256; / <<
49 .map_flags = BPF_F_MMAPABLE; <<
50 .map_name = "example_array"; <<
51 }; <<
52 20
53 fd = bpf(BPF_MAP_CREATE, &attr, sizeof(att !! 21 - create or update key/value pair in a given map
>> 22 ``err = bpf(BPF_MAP_UPDATE_ELEM, union bpf_attr *attr, u32 size)``
>> 23 using attr->map_fd, attr->key, attr->value
>> 24 returns zero or negative error
54 25
55 Returns a process-local file descriptor on suc !! 26 - find and delete element by key in a given map
56 failure. The map can be deleted by calling ``c !! 27 ``err = bpf(BPF_MAP_DELETE_ELEM, union bpf_attr *attr, u32 size)``
57 file descriptors will be deleted automatically !! 28 using attr->map_fd, attr->key
58 29
59 .. note:: Valid characters for ``map_name`` ar !! 30 - to delete map: close(fd)
60 ``'_'`` and ``'.'``. !! 31 Exiting process will delete maps automatically
61 32
62 **BPF_MAP_LOOKUP_ELEM** !! 33 userspace programs use this syscall to create/access maps that eBPF programs
>> 34 are concurrently updating.
63 35
64 Lookup key in a given map using ``attr->map_fd !! 36 maps can have different types: hash, array, bloom filter, radix-tree, etc.
65 ``attr->value``. Returns zero and stores found <<
66 success, or negative error on failure. <<
67 37
68 **BPF_MAP_UPDATE_ELEM** !! 38 The map is defined by:
69 39
70 Create or update key/value pair in a given map !! 40 - type
71 ``attr->value``. Returns zero on success or ne !! 41 - max number of elements
>> 42 - key size in bytes
>> 43 - value size in bytes
72 44
73 **BPF_MAP_DELETE_ELEM** !! 45 Map Types
>> 46 =========
74 47
75 Find and delete element by key in a given map !! 48 .. toctree::
76 ``attr->key``. Returns zero on success or nega !! 49 :maxdepth: 1
>> 50 :glob:
77 51
78 .. Links: !! 52 map_*
79 .. _man-pages: https://www.kernel.org/doc/man- <<
80 .. _bpf(2): https://man7.org/linux/man-pages/m <<
81 .. _bpf-helpers(7): https://man7.org/linux/man <<
82 .. _ebpf-syscall: https://docs.kernel.org/user <<
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