tools/bpf/bpftool/Documentation/bpftool-map.rst

.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)

================
bpftool-map
================
-------------------------------------------------------------------------------
tool for inspection and simple manipulation of eBPF maps
-------------------------------------------------------------------------------

:Manual section: 8

.. include:: substitutions.rst

SYNOPSIS
========

**bpftool** [*OPTIONS*] **map** *COMMAND*

*OPTIONS* := { |COMMON_OPTIONS| | { **-f** | **--bpffs** } | { **-n** | **--nomount** } }

*COMMANDS* :=
{ **show** | **list** | **create** | **dump** | **update** | **lookup** | **getnext** |
**delete** | **pin** | **help** }

MAP COMMANDS
=============

| **bpftool** **map** { **show** | **list** }   [*MAP*]
| **bpftool** **map create**     *FILE* **type** *TYPE* **key** *KEY_SIZE* **value** *VALUE_SIZE* \
|     **entries** *MAX_ENTRIES* **name** *NAME* [**flags** *FLAGS*] [**inner_map** *MAP*] \
|     [**offload_dev** *NAME*]
| **bpftool** **map dump**       *MAP*
| **bpftool** **map update**     *MAP* [**key** *DATA*] [**value** *VALUE*] [*UPDATE_FLAGS*]
| **bpftool** **map lookup**     *MAP* [**key** *DATA*]
| **bpftool** **map getnext**    *MAP* [**key** *DATA*]
| **bpftool** **map delete**     *MAP*  **key** *DATA*
| **bpftool** **map pin**        *MAP*  *FILE*
| **bpftool** **map event_pipe** *MAP* [**cpu** *N* **index** *M*]
| **bpftool** **map peek**       *MAP*
| **bpftool** **map push**       *MAP* **value** *VALUE*
| **bpftool** **map pop**        *MAP*
| **bpftool** **map enqueue**    *MAP* **value** *VALUE*
| **bpftool** **map dequeue**    *MAP*
| **bpftool** **map freeze**     *MAP*
| **bpftool** **map help**
|
| *MAP* := { **id** *MAP_ID* | **pinned** *FILE* | **name** *MAP_NAME* }
| *DATA* := { [**hex**] *BYTES* }
| *PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* | **name** *PROG_NAME* }
| *VALUE* := { *DATA* | *MAP* | *PROG* }
| *UPDATE_FLAGS* := { **any** | **exist** | **noexist** }
| *TYPE* := { **hash** | **array** | **prog_array** | **perf_event_array** | **percpu_hash**
|     | **percpu_array** | **stack_trace** | **cgroup_array** | **lru_hash**
|     | **lru_percpu_hash** | **lpm_trie** | **array_of_maps** | **hash_of_maps**
|     | **devmap** | **devmap_hash** | **sockmap** | **cpumap** | **xskmap** | **sockhash**
|     | **cgroup_storage** | **reuseport_sockarray** | **percpu_cgroup_storage**
|     | **queue** | **stack** | **sk_storage** | **struct_ops** | **ringbuf** | **inode_storage**
|     | **task_storage** | **bloom_filter** | **user_ringbuf** | **cgrp_storage** | **arena**
|     | **insn_array** | **rhash** }

DESCRIPTION
===========
bpftool map { show | list }   [*MAP*]
    Show information about loaded maps.  If *MAP* is specified show information
    only about given maps, otherwise list all maps currently loaded on the
    system.  In case of **name**, *MAP* may match several maps which will all
    be shown.

    Output will start with map ID followed by map type and zero or more named
    attributes (depending on kernel version).

    Since Linux 5.8 bpftool is able to discover information about processes
    that hold open file descriptors (FDs) against BPF maps. On such kernels
    bpftool will automatically emit this information as well.

bpftool map create *FILE* type *TYPE* key *KEY_SIZE* value *VALUE_SIZE*  entries *MAX_ENTRIES* name *NAME* [flags *FLAGS*] [inner_map *MAP*] [offload_dev *NAME*]
    Create a new map with given parameters and pin it to *bpffs* as *FILE*.

    *FLAGS* should be an integer which is the combination of desired flags,
    e.g. 1024 for **BPF_F_MMAPABLE** (see bpf.h UAPI header for existing
    flags).

    To create maps of type array-of-maps or hash-of-maps, the **inner_map**
    keyword must be used to pass an inner map. The kernel needs it to collect
    metadata related to the inner maps that the new map will work with.

    Keyword **offload_dev** expects a network interface name, and is used to
    request hardware offload for the map.

bpftool map dump    *MAP*
    Dump all entries in a given *MAP*.  In case of **name**, *MAP* may match
    several maps which will all be dumped.

bpftool map update  *MAP* [key *DATA*] [value *VALUE*] [*UPDATE_FLAGS*]
    Update map entry for a given *KEY*.

    *UPDATE_FLAGS* can be one of: **any** update existing entry or add if
    doesn't exit; **exist** update only if entry already exists; **noexist**
    update only if entry doesn't exist.

    If the **hex** keyword is provided in front of the bytes sequence, the
    bytes are parsed as hexadecimal values, even if no "0x" prefix is added. If
    the keyword is not provided, then the bytes are parsed as decimal values,
    unless a "0x" prefix (for hexadecimal) or a "0" prefix (for octal) is
    provided.

bpftool map lookup  *MAP* [key *DATA*]
    Lookup **key** in the map.

bpftool map getnext *MAP* [key *DATA*]
    Get next key.  If *key* is not specified, get first key.

bpftool map delete  *MAP*  key *DATA*
    Remove entry from the map.

bpftool map pin     *MAP*  *FILE*
    Pin map *MAP* as *FILE*.

    Note: *FILE* must be located in *bpffs* mount. It must not contain a dot
    character ('.'), which is reserved for future extensions of *bpffs*.

bpftool map event_pipe *MAP* [cpu *N* index *M*]
    Read events from a **BPF_MAP_TYPE_PERF_EVENT_ARRAY** map.

    Install perf rings into a perf event array map and dump output of any
    **bpf_perf_event_output**\ () call in the kernel. By default read the
    number of CPUs on the system and install perf ring for each CPU in the
    corresponding index in the array.

    If **cpu** and **index** are specified, install perf ring for given **cpu**
    at **index** in the array (single ring).

    Note that installing a perf ring into an array will silently replace any
    existing ring.  Any other application will stop receiving events if it
    installed its rings earlier.

bpftool map peek  *MAP*
    Peek next value in the queue or stack.

bpftool map push  *MAP* value *VALUE*
    Push *VALUE* onto the stack.

bpftool map pop  *MAP*
    Pop and print value from the stack.

bpftool map enqueue  *MAP* value *VALUE*
    Enqueue *VALUE* into the queue.

bpftool map dequeue  *MAP*
    Dequeue and print value from the queue.

bpftool map freeze  *MAP*
    Freeze the map as read-only from user space. Entries from a frozen map can
    not longer be updated or deleted with the **bpf**\ () system call. This
    operation is not reversible, and the map remains immutable from user space
    until its destruction. However, read and write permissions for BPF programs
    to the map remain unchanged.

bpftool map help
    Print short help message.

OPTIONS
=======
.. include:: common_options.rst

-f, --bpffs
    Show file names of pinned maps.

-n, --nomount
    Do not automatically attempt to mount any virtual file system (such as
    tracefs or BPF virtual file system) when necessary.

EXAMPLES
========
**# bpftool map show**

::

  10: hash  name some_map  flags 0x0
        key 4B  value 8B  max_entries 2048  memlock 167936B
        pids systemd(1)

The following three commands are equivalent:

|
| **# bpftool map update id 10 key hex   20   c4   b7   00 value hex   0f   ff   ff   ab   01   02   03   4c**
| **# bpftool map update id 10 key     0x20 0xc4 0xb7 0x00 value     0x0f 0xff 0xff 0xab 0x01 0x02 0x03 0x4c**
| **# bpftool map update id 10 key       32  196  183    0 value       15  255  255  171    1    2    3   76**

**# bpftool map lookup id 10 key 0 1 2 3**

::

  key: 00 01 02 03 value: 00 01 02 03 04 05 06 07


**# bpftool map dump id 10**

::

  key: 00 01 02 03  value: 00 01 02 03 04 05 06 07
  key: 0d 00 07 00  value: 02 00 00 00 01 02 03 04
  Found 2 elements

**# bpftool map getnext id 10 key 0 1 2 3**

::

  key:
  00 01 02 03
  next key:
  0d 00 07 00

|
| **# mount -t bpf none /sys/fs/bpf/**
| **# bpftool map pin id 10 /sys/fs/bpf/map**
| **# bpftool map del pinned /sys/fs/bpf/map key 13 00 07 00**

Note that map update can also be used in order to change the program references
hold by a program array map. This can be used, for example, to change the
programs used for tail-call jumps at runtime, without having to reload the
entry-point program. Below is an example for this use case: we load a program
defining a prog array map, and with a main function that contains a tail call
to other programs that can be used either to "process" packets or to "debug"
processing. Note that the prog array map MUST be pinned into the BPF virtual
file system for the map update to work successfully, as kernel flushes prog
array maps when they have no more references from user space (and the update
would be lost as soon as bpftool exits).

|
| **# bpftool prog loadall tail_calls.o /sys/fs/bpf/foo type xdp**
| **# bpftool prog --bpffs**

::

  545: xdp  name main_func  tag 674b4b5597193dc3  gpl
          loaded_at 2018-12-12T15:02:58+0000  uid 0
          xlated 240B  jited 257B  memlock 4096B  map_ids 294
          pinned /sys/fs/bpf/foo/xdp
  546: xdp  name bpf_func_process  tag e369a529024751fc  gpl
          loaded_at 2018-12-12T15:02:58+0000  uid 0
          xlated 200B  jited 164B  memlock 4096B
          pinned /sys/fs/bpf/foo/process
  547: xdp  name bpf_func_debug  tag 0b597868bc7f0976  gpl
          loaded_at 2018-12-12T15:02:58+0000  uid 0
          xlated 200B  jited 164B  memlock 4096B
          pinned /sys/fs/bpf/foo/debug

**# bpftool map**

::

  294: prog_array  name jmp_table  flags 0x0
          key 4B  value 4B  max_entries 1  memlock 4096B
          owner_prog_type xdp  owner jited

|
| **# bpftool map pin id 294 /sys/fs/bpf/bar**
| **# bpftool map dump pinned /sys/fs/bpf/bar**

::

  Found 0 elements

|
| **# bpftool map update pinned /sys/fs/bpf/bar key 0 0 0 0 value pinned /sys/fs/bpf/foo/debug**
| **# bpftool map dump pinned /sys/fs/bpf/bar**

::

  key: 00 00 00 00  value: 22 02 00 00
  Found 1 element